btrfs: fix race between finishing block group creation and its item update

[platform/kernel/linux-rpi.git] / fs / btrfs / file.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 */

#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/falloc.h>
#include <linux/writeback.h>
#include <linux/compat.h>
#include <linux/slab.h>
#include <linux/btrfs.h>
#include <linux/uio.h>
#include <linux/iversion.h>
#include <linux/fsverity.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "print-tree.h"
#include "tree-log.h"
#include "locking.h"
#include "volumes.h"
#include "qgroup.h"
#include "compression.h"
#include "delalloc-space.h"
#include "reflink.h"
#include "subpage.h"
#include "fs.h"
#include "accessors.h"
#include "extent-tree.h"
#include "file-item.h"
#include "ioctl.h"
#include "file.h"
#include "super.h"

/* simple helper to fault in pages and copy.  This should go away
 * and be replaced with calls into generic code.
 */
static noinline int btrfs_copy_from_user(loff_t pos, size_t write_bytes,
                                         struct page **prepared_pages,
                                         struct iov_iter *i)
{
        size_t copied = 0;
        size_t total_copied = 0;
        int pg = 0;
        int offset = offset_in_page(pos);

        while (write_bytes > 0) {
                size_t count = min_t(size_t,
                                     PAGE_SIZE - offset, write_bytes);
                struct page *page = prepared_pages[pg];
                /*
                 * Copy data from userspace to the current page
                 */
                copied = copy_page_from_iter_atomic(page, offset, count, i);

                /* Flush processor's dcache for this page */
                flush_dcache_page(page);

                /*
                 * if we get a partial write, we can end up with
                 * partially up to date pages.  These add
                 * a lot of complexity, so make sure they don't
                 * happen by forcing this copy to be retried.
                 *
                 * The rest of the btrfs_file_write code will fall
                 * back to page at a time copies after we return 0.
                 */
                if (unlikely(copied < count)) {
                        if (!PageUptodate(page)) {
                                iov_iter_revert(i, copied);
                                copied = 0;
                        }
                        if (!copied)
                                break;
                }

                write_bytes -= copied;
                total_copied += copied;
                offset += copied;
                if (offset == PAGE_SIZE) {
                        pg++;
                        offset = 0;
                }
        }
        return total_copied;
}

/*
 * unlocks pages after btrfs_file_write is done with them
 */
static void btrfs_drop_pages(struct btrfs_fs_info *fs_info,
                             struct page **pages, size_t num_pages,
                             u64 pos, u64 copied)
{
        size_t i;
        u64 block_start = round_down(pos, fs_info->sectorsize);
        u64 block_len = round_up(pos + copied, fs_info->sectorsize) - block_start;

        ASSERT(block_len <= U32_MAX);
        for (i = 0; i < num_pages; i++) {
                /* page checked is some magic around finding pages that
                 * have been modified without going through btrfs_set_page_dirty
                 * clear it here. There should be no need to mark the pages
                 * accessed as prepare_pages should have marked them accessed
                 * in prepare_pages via find_or_create_page()
                 */
                btrfs_page_clamp_clear_checked(fs_info, pages[i], block_start,
                                               block_len);
                unlock_page(pages[i]);
                put_page(pages[i]);
        }
}

/*
 * After btrfs_copy_from_user(), update the following things for delalloc:
 * - Mark newly dirtied pages as DELALLOC in the io tree.
 *   Used to advise which range is to be written back.
 * - Mark modified pages as Uptodate/Dirty and not needing COW fixup
 * - Update inode size for past EOF write
 */
int btrfs_dirty_pages(struct btrfs_inode *inode, struct page **pages,
                      size_t num_pages, loff_t pos, size_t write_bytes,
                      struct extent_state **cached, bool noreserve)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        int err = 0;
        int i;
        u64 num_bytes;
        u64 start_pos;
        u64 end_of_last_block;
        u64 end_pos = pos + write_bytes;
        loff_t isize = i_size_read(&inode->vfs_inode);
        unsigned int extra_bits = 0;

        if (write_bytes == 0)
                return 0;

        if (noreserve)
                extra_bits |= EXTENT_NORESERVE;

        start_pos = round_down(pos, fs_info->sectorsize);
        num_bytes = round_up(write_bytes + pos - start_pos,
                             fs_info->sectorsize);
        ASSERT(num_bytes <= U32_MAX);

        end_of_last_block = start_pos + num_bytes - 1;

        /*
         * The pages may have already been dirty, clear out old accounting so
         * we can set things up properly
         */
        clear_extent_bit(&inode->io_tree, start_pos, end_of_last_block,
                         EXTENT_DELALLOC | EXTENT_DO_ACCOUNTING | EXTENT_DEFRAG,
                         cached);

        err = btrfs_set_extent_delalloc(inode, start_pos, end_of_last_block,
                                        extra_bits, cached);
        if (err)
                return err;

        for (i = 0; i < num_pages; i++) {
                struct page *p = pages[i];

                btrfs_page_clamp_set_uptodate(fs_info, p, start_pos, num_bytes);
                btrfs_page_clamp_clear_checked(fs_info, p, start_pos, num_bytes);
                btrfs_page_clamp_set_dirty(fs_info, p, start_pos, num_bytes);
        }

        /*
         * we've only changed i_size in ram, and we haven't updated
         * the disk i_size.  There is no need to log the inode
         * at this time.
         */
        if (end_pos > isize)
                i_size_write(&inode->vfs_inode, end_pos);
        return 0;
}

/*
 * this is very complex, but the basic idea is to drop all extents
 * in the range start - end.  hint_block is filled in with a block number
 * that would be a good hint to the block allocator for this file.
 *
 * If an extent intersects the range but is not entirely inside the range
 * it is either truncated or split.  Anything entirely inside the range
 * is deleted from the tree.
 *
 * Note: the VFS' inode number of bytes is not updated, it's up to the caller
 * to deal with that. We set the field 'bytes_found' of the arguments structure
 * with the number of allocated bytes found in the target range, so that the
 * caller can update the inode's number of bytes in an atomic way when
 * replacing extents in a range to avoid races with stat(2).
 */
int btrfs_drop_extents(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root, struct btrfs_inode *inode,
                       struct btrfs_drop_extents_args *args)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct extent_buffer *leaf;
        struct btrfs_file_extent_item *fi;
        struct btrfs_ref ref = { 0 };
        struct btrfs_key key;
        struct btrfs_key new_key;
        u64 ino = btrfs_ino(inode);
        u64 search_start = args->start;
        u64 disk_bytenr = 0;
        u64 num_bytes = 0;
        u64 extent_offset = 0;
        u64 extent_end = 0;
        u64 last_end = args->start;
        int del_nr = 0;
        int del_slot = 0;
        int extent_type;
        int recow;
        int ret;
        int modify_tree = -1;
        int update_refs;
        int found = 0;
        struct btrfs_path *path = args->path;

        args->bytes_found = 0;
        args->extent_inserted = false;

        /* Must always have a path if ->replace_extent is true */
        ASSERT(!(args->replace_extent && !args->path));

        if (!path) {
                path = btrfs_alloc_path();
                if (!path) {
                        ret = -ENOMEM;
                        goto out;
                }
        }

        if (args->drop_cache)
                btrfs_drop_extent_map_range(inode, args->start, args->end - 1, false);

        if (args->start >= inode->disk_i_size && !args->replace_extent)
                modify_tree = 0;

        update_refs = (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID);
        while (1) {
                recow = 0;
                ret = btrfs_lookup_file_extent(trans, root, path, ino,
                                               search_start, modify_tree);
                if (ret < 0)
                        break;
                if (ret > 0 && path->slots[0] > 0 && search_start == args->start) {
                        leaf = path->nodes[0];
                        btrfs_item_key_to_cpu(leaf, &key, path->slots[0] - 1);
                        if (key.objectid == ino &&
                            key.type == BTRFS_EXTENT_DATA_KEY)
                                path->slots[0]--;
                }
                ret = 0;
next_slot:
                leaf = path->nodes[0];
                if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                        BUG_ON(del_nr > 0);
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                break;
                        if (ret > 0) {
                                ret = 0;
                                break;
                        }
                        leaf = path->nodes[0];
                        recow = 1;
                }

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);

                if (key.objectid > ino)
                        break;
                if (WARN_ON_ONCE(key.objectid < ino) ||
                    key.type < BTRFS_EXTENT_DATA_KEY) {
                        ASSERT(del_nr == 0);
                        path->slots[0]++;
                        goto next_slot;
                }
                if (key.type > BTRFS_EXTENT_DATA_KEY || key.offset >= args->end)
                        break;

                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                extent_type = btrfs_file_extent_type(leaf, fi);

                if (extent_type == BTRFS_FILE_EXTENT_REG ||
                    extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
                        disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
                        num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
                        extent_offset = btrfs_file_extent_offset(leaf, fi);
                        extent_end = key.offset +
                                btrfs_file_extent_num_bytes(leaf, fi);
                } else if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                        extent_end = key.offset +
                                btrfs_file_extent_ram_bytes(leaf, fi);
                } else {
                        /* can't happen */
                        BUG();
                }

                /*
                 * Don't skip extent items representing 0 byte lengths. They
                 * used to be created (bug) if while punching holes we hit
                 * -ENOSPC condition. So if we find one here, just ensure we
                 * delete it, otherwise we would insert a new file extent item
                 * with the same key (offset) as that 0 bytes length file
                 * extent item in the call to setup_items_for_insert() later
                 * in this function.
                 */
                if (extent_end == key.offset && extent_end >= search_start) {
                        last_end = extent_end;
                        goto delete_extent_item;
                }

                if (extent_end <= search_start) {
                        path->slots[0]++;
                        goto next_slot;
                }

                found = 1;
                search_start = max(key.offset, args->start);
                if (recow || !modify_tree) {
                        modify_tree = -1;
                        btrfs_release_path(path);
                        continue;
                }

                /*
                 *     | - range to drop - |
                 *  | -------- extent -------- |
                 */
                if (args->start > key.offset && args->end < extent_end) {
                        BUG_ON(del_nr > 0);
                        if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                ret = -EOPNOTSUPP;
                                break;
                        }

                        memcpy(&new_key, &key, sizeof(new_key));
                        new_key.offset = args->start;
                        ret = btrfs_duplicate_item(trans, root, path,
                                                   &new_key);
                        if (ret == -EAGAIN) {
                                btrfs_release_path(path);
                                continue;
                        }
                        if (ret < 0)
                                break;

                        leaf = path->nodes[0];
                        fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        args->start - key.offset);

                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);

                        extent_offset += args->start - key.offset;
                        btrfs_set_file_extent_offset(leaf, fi, extent_offset);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        extent_end - args->start);
                        btrfs_mark_buffer_dirty(leaf);

                        if (update_refs && disk_bytenr > 0) {
                                btrfs_init_generic_ref(&ref,
                                                BTRFS_ADD_DELAYED_REF,
                                                disk_bytenr, num_bytes, 0);
                                btrfs_init_data_ref(&ref,
                                                root->root_key.objectid,
                                                new_key.objectid,
                                                args->start - extent_offset,
                                                0, false);
                                ret = btrfs_inc_extent_ref(trans, &ref);
                                if (ret) {
                                        btrfs_abort_transaction(trans, ret);
                                        break;
                                }
                        }
                        key.offset = args->start;
                }
                /*
                 * From here on out we will have actually dropped something, so
                 * last_end can be updated.
                 */
                last_end = extent_end;

                /*
                 *  | ---- range to drop ----- |
                 *      | -------- extent -------- |
                 */
                if (args->start <= key.offset && args->end < extent_end) {
                        if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                ret = -EOPNOTSUPP;
                                break;
                        }

                        memcpy(&new_key, &key, sizeof(new_key));
                        new_key.offset = args->end;
                        btrfs_set_item_key_safe(fs_info, path, &new_key);

                        extent_offset += args->end - key.offset;
                        btrfs_set_file_extent_offset(leaf, fi, extent_offset);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        extent_end - args->end);
                        btrfs_mark_buffer_dirty(leaf);
                        if (update_refs && disk_bytenr > 0)
                                args->bytes_found += args->end - key.offset;
                        break;
                }

                search_start = extent_end;
                /*
                 *       | ---- range to drop ----- |
                 *  | -------- extent -------- |
                 */
                if (args->start > key.offset && args->end >= extent_end) {
                        BUG_ON(del_nr > 0);
                        if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                ret = -EOPNOTSUPP;
                                break;
                        }

                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        args->start - key.offset);
                        btrfs_mark_buffer_dirty(leaf);
                        if (update_refs && disk_bytenr > 0)
                                args->bytes_found += extent_end - args->start;
                        if (args->end == extent_end)
                                break;

                        path->slots[0]++;
                        goto next_slot;
                }

                /*
                 *  | ---- range to drop ----- |
                 *    | ------ extent ------ |
                 */
                if (args->start <= key.offset && args->end >= extent_end) {
delete_extent_item:
                        if (del_nr == 0) {
                                del_slot = path->slots[0];
                                del_nr = 1;
                        } else {
                                BUG_ON(del_slot + del_nr != path->slots[0]);
                                del_nr++;
                        }

                        if (update_refs &&
                            extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                args->bytes_found += extent_end - key.offset;
                                extent_end = ALIGN(extent_end,
                                                   fs_info->sectorsize);
                        } else if (update_refs && disk_bytenr > 0) {
                                btrfs_init_generic_ref(&ref,
                                                BTRFS_DROP_DELAYED_REF,
                                                disk_bytenr, num_bytes, 0);
                                btrfs_init_data_ref(&ref,
                                                root->root_key.objectid,
                                                key.objectid,
                                                key.offset - extent_offset, 0,
                                                false);
                                ret = btrfs_free_extent(trans, &ref);
                                if (ret) {
                                        btrfs_abort_transaction(trans, ret);
                                        break;
                                }
                                args->bytes_found += extent_end - key.offset;
                        }

                        if (args->end == extent_end)
                                break;

                        if (path->slots[0] + 1 < btrfs_header_nritems(leaf)) {
                                path->slots[0]++;
                                goto next_slot;
                        }

                        ret = btrfs_del_items(trans, root, path, del_slot,
                                              del_nr);
                        if (ret) {
                                btrfs_abort_transaction(trans, ret);
                                break;
                        }

                        del_nr = 0;
                        del_slot = 0;

                        btrfs_release_path(path);
                        continue;
                }

                BUG();
        }

        if (!ret && del_nr > 0) {
                /*
                 * Set path->slots[0] to first slot, so that after the delete
                 * if items are move off from our leaf to its immediate left or
                 * right neighbor leafs, we end up with a correct and adjusted
                 * path->slots[0] for our insertion (if args->replace_extent).
                 */
                path->slots[0] = del_slot;
                ret = btrfs_del_items(trans, root, path, del_slot, del_nr);
                if (ret)
                        btrfs_abort_transaction(trans, ret);
        }

        leaf = path->nodes[0];
        /*
         * If btrfs_del_items() was called, it might have deleted a leaf, in
         * which case it unlocked our path, so check path->locks[0] matches a
         * write lock.
         */
        if (!ret && args->replace_extent &&
            path->locks[0] == BTRFS_WRITE_LOCK &&
            btrfs_leaf_free_space(leaf) >=
            sizeof(struct btrfs_item) + args->extent_item_size) {

                key.objectid = ino;
                key.type = BTRFS_EXTENT_DATA_KEY;
                key.offset = args->start;
                if (!del_nr && path->slots[0] < btrfs_header_nritems(leaf)) {
                        struct btrfs_key slot_key;

                        btrfs_item_key_to_cpu(leaf, &slot_key, path->slots[0]);
                        if (btrfs_comp_cpu_keys(&key, &slot_key) > 0)
                                path->slots[0]++;
                }
                btrfs_setup_item_for_insert(root, path, &key, args->extent_item_size);
                args->extent_inserted = true;
        }

        if (!args->path)
                btrfs_free_path(path);
        else if (!args->extent_inserted)
                btrfs_release_path(path);
out:
        args->drop_end = found ? min(args->end, last_end) : args->end;

        return ret;
}

static int extent_mergeable(struct extent_buffer *leaf, int slot,
                            u64 objectid, u64 bytenr, u64 orig_offset,
                            u64 *start, u64 *end)
{
        struct btrfs_file_extent_item *fi;
        struct btrfs_key key;
        u64 extent_end;

        if (slot < 0 || slot >= btrfs_header_nritems(leaf))
                return 0;

        btrfs_item_key_to_cpu(leaf, &key, slot);
        if (key.objectid != objectid || key.type != BTRFS_EXTENT_DATA_KEY)
                return 0;

        fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
        if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_REG ||
            btrfs_file_extent_disk_bytenr(leaf, fi) != bytenr ||
            btrfs_file_extent_offset(leaf, fi) != key.offset - orig_offset ||
            btrfs_file_extent_compression(leaf, fi) ||
            btrfs_file_extent_encryption(leaf, fi) ||
            btrfs_file_extent_other_encoding(leaf, fi))
                return 0;

        extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
        if ((*start && *start != key.offset) || (*end && *end != extent_end))
                return 0;

        *start = key.offset;
        *end = extent_end;
        return 1;
}

/*
 * Mark extent in the range start - end as written.
 *
 * This changes extent type from 'pre-allocated' to 'regular'. If only
 * part of extent is marked as written, the extent will be split into
 * two or three.
 */
int btrfs_mark_extent_written(struct btrfs_trans_handle *trans,
                              struct btrfs_inode *inode, u64 start, u64 end)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root = inode->root;
        struct extent_buffer *leaf;
        struct btrfs_path *path;
        struct btrfs_file_extent_item *fi;
        struct btrfs_ref ref = { 0 };
        struct btrfs_key key;
        struct btrfs_key new_key;
        u64 bytenr;
        u64 num_bytes;
        u64 extent_end;
        u64 orig_offset;
        u64 other_start;
        u64 other_end;
        u64 split;
        int del_nr = 0;
        int del_slot = 0;
        int recow;
        int ret = 0;
        u64 ino = btrfs_ino(inode);

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
again:
        recow = 0;
        split = start;
        key.objectid = ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = split;

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret < 0)
                goto out;
        if (ret > 0 && path->slots[0] > 0)
                path->slots[0]--;

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        if (key.objectid != ino ||
            key.type != BTRFS_EXTENT_DATA_KEY) {
                ret = -EINVAL;
                btrfs_abort_transaction(trans, ret);
                goto out;
        }
        fi = btrfs_item_ptr(leaf, path->slots[0],
                            struct btrfs_file_extent_item);
        if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_PREALLOC) {
                ret = -EINVAL;
                btrfs_abort_transaction(trans, ret);
                goto out;
        }
        extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
        if (key.offset > start || extent_end < end) {
                ret = -EINVAL;
                btrfs_abort_transaction(trans, ret);
                goto out;
        }

        bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
        num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
        orig_offset = key.offset - btrfs_file_extent_offset(leaf, fi);
        memcpy(&new_key, &key, sizeof(new_key));

        if (start == key.offset && end < extent_end) {
                other_start = 0;
                other_end = start;
                if (extent_mergeable(leaf, path->slots[0] - 1,
                                     ino, bytenr, orig_offset,
                                     &other_start, &other_end)) {
                        new_key.offset = end;
                        btrfs_set_item_key_safe(fs_info, path, &new_key);
                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        extent_end - end);
                        btrfs_set_file_extent_offset(leaf, fi,
                                                     end - orig_offset);
                        fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        end - other_start);
                        btrfs_mark_buffer_dirty(leaf);
                        goto out;
                }
        }

        if (start > key.offset && end == extent_end) {
                other_start = end;
                other_end = 0;
                if (extent_mergeable(leaf, path->slots[0] + 1,
                                     ino, bytenr, orig_offset,
                                     &other_start, &other_end)) {
                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        start - key.offset);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        path->slots[0]++;
                        new_key.offset = start;
                        btrfs_set_item_key_safe(fs_info, path, &new_key);

                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        other_end - start);
                        btrfs_set_file_extent_offset(leaf, fi,
                                                     start - orig_offset);
                        btrfs_mark_buffer_dirty(leaf);
                        goto out;
                }
        }

        while (start > key.offset || end < extent_end) {
                if (key.offset == start)
                        split = end;

                new_key.offset = split;
                ret = btrfs_duplicate_item(trans, root, path, &new_key);
                if (ret == -EAGAIN) {
                        btrfs_release_path(path);
                        goto again;
                }
                if (ret < 0) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }

                leaf = path->nodes[0];
                fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                                    struct btrfs_file_extent_item);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_set_file_extent_num_bytes(leaf, fi,
                                                split - key.offset);

                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);

                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_set_file_extent_offset(leaf, fi, split - orig_offset);
                btrfs_set_file_extent_num_bytes(leaf, fi,
                                                extent_end - split);
                btrfs_mark_buffer_dirty(leaf);

                btrfs_init_generic_ref(&ref, BTRFS_ADD_DELAYED_REF, bytenr,
                                       num_bytes, 0);
                btrfs_init_data_ref(&ref, root->root_key.objectid, ino,
                                    orig_offset, 0, false);
                ret = btrfs_inc_extent_ref(trans, &ref);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }

                if (split == start) {
                        key.offset = start;
                } else {
                        if (start != key.offset) {
                                ret = -EINVAL;
                                btrfs_abort_transaction(trans, ret);
                                goto out;
                        }
                        path->slots[0]--;
                        extent_end = end;
                }
                recow = 1;
        }

        other_start = end;
        other_end = 0;
        btrfs_init_generic_ref(&ref, BTRFS_DROP_DELAYED_REF, bytenr,
                               num_bytes, 0);
        btrfs_init_data_ref(&ref, root->root_key.objectid, ino, orig_offset,
                            0, false);
        if (extent_mergeable(leaf, path->slots[0] + 1,
                             ino, bytenr, orig_offset,
                             &other_start, &other_end)) {
                if (recow) {
                        btrfs_release_path(path);
                        goto again;
                }
                extent_end = other_end;
                del_slot = path->slots[0] + 1;
                del_nr++;
                ret = btrfs_free_extent(trans, &ref);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
        }
        other_start = 0;
        other_end = start;
        if (extent_mergeable(leaf, path->slots[0] - 1,
                             ino, bytenr, orig_offset,
                             &other_start, &other_end)) {
                if (recow) {
                        btrfs_release_path(path);
                        goto again;
                }
                key.offset = other_start;
                del_slot = path->slots[0];
                del_nr++;
                ret = btrfs_free_extent(trans, &ref);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
        }
        if (del_nr == 0) {
                fi = btrfs_item_ptr(leaf, path->slots[0],
                           struct btrfs_file_extent_item);
                btrfs_set_file_extent_type(leaf, fi,
                                           BTRFS_FILE_EXTENT_REG);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_mark_buffer_dirty(leaf);
        } else {
                fi = btrfs_item_ptr(leaf, del_slot - 1,
                           struct btrfs_file_extent_item);
                btrfs_set_file_extent_type(leaf, fi,
                                           BTRFS_FILE_EXTENT_REG);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_set_file_extent_num_bytes(leaf, fi,
                                                extent_end - key.offset);
                btrfs_mark_buffer_dirty(leaf);

                ret = btrfs_del_items(trans, root, path, del_slot, del_nr);
                if (ret < 0) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
        }
out:
        btrfs_free_path(path);
        return ret;
}

/*
 * on error we return an unlocked page and the error value
 * on success we return a locked page and 0
 */
static int prepare_uptodate_page(struct inode *inode,
                                 struct page *page, u64 pos,
                                 bool force_uptodate)
{
        struct folio *folio = page_folio(page);
        int ret = 0;

        if (((pos & (PAGE_SIZE - 1)) || force_uptodate) &&
            !PageUptodate(page)) {
                ret = btrfs_read_folio(NULL, folio);
                if (ret)
                        return ret;
                lock_page(page);
                if (!PageUptodate(page)) {
                        unlock_page(page);
                        return -EIO;
                }

                /*
                 * Since btrfs_read_folio() will unlock the folio before it
                 * returns, there is a window where btrfs_release_folio() can be
                 * called to release the page.  Here we check both inode
                 * mapping and PagePrivate() to make sure the page was not
                 * released.
                 *
                 * The private flag check is essential for subpage as we need
                 * to store extra bitmap using page->private.
                 */
                if (page->mapping != inode->i_mapping || !PagePrivate(page)) {
                        unlock_page(page);
                        return -EAGAIN;
                }
        }
        return 0;
}

static unsigned int get_prepare_fgp_flags(bool nowait)
{
        unsigned int fgp_flags = FGP_LOCK | FGP_ACCESSED | FGP_CREAT;

        if (nowait)
                fgp_flags |= FGP_NOWAIT;

        return fgp_flags;
}

static gfp_t get_prepare_gfp_flags(struct inode *inode, bool nowait)
{
        gfp_t gfp;

        gfp = btrfs_alloc_write_mask(inode->i_mapping);
        if (nowait) {
                gfp &= ~__GFP_DIRECT_RECLAIM;
                gfp |= GFP_NOWAIT;
        }

        return gfp;
}

/*
 * this just gets pages into the page cache and locks them down.
 */
static noinline int prepare_pages(struct inode *inode, struct page **pages,
                                  size_t num_pages, loff_t pos,
                                  size_t write_bytes, bool force_uptodate,
                                  bool nowait)
{
        int i;
        unsigned long index = pos >> PAGE_SHIFT;
        gfp_t mask = get_prepare_gfp_flags(inode, nowait);
        unsigned int fgp_flags = get_prepare_fgp_flags(nowait);
        int err = 0;
        int faili;

        for (i = 0; i < num_pages; i++) {
again:
                pages[i] = pagecache_get_page(inode->i_mapping, index + i,
                                              fgp_flags, mask | __GFP_WRITE);
                if (!pages[i]) {
                        faili = i - 1;
                        if (nowait)
                                err = -EAGAIN;
                        else
                                err = -ENOMEM;
                        goto fail;
                }

                err = set_page_extent_mapped(pages[i]);
                if (err < 0) {
                        faili = i;
                        goto fail;
                }

                if (i == 0)
                        err = prepare_uptodate_page(inode, pages[i], pos,
                                                    force_uptodate);
                if (!err && i == num_pages - 1)
                        err = prepare_uptodate_page(inode, pages[i],
                                                    pos + write_bytes, false);
                if (err) {
                        put_page(pages[i]);
                        if (!nowait && err == -EAGAIN) {
                                err = 0;
                                goto again;
                        }
                        faili = i - 1;
                        goto fail;
                }
                wait_on_page_writeback(pages[i]);
        }

        return 0;
fail:
        while (faili >= 0) {
                unlock_page(pages[faili]);
                put_page(pages[faili]);
                faili--;
        }
        return err;

}

/*
 * This function locks the extent and properly waits for data=ordered extents
 * to finish before allowing the pages to be modified if need.
 *
 * The return value:
 * 1 - the extent is locked
 * 0 - the extent is not locked, and everything is OK
 * -EAGAIN - need re-prepare the pages
 * the other < 0 number - Something wrong happens
 */
static noinline int
lock_and_cleanup_extent_if_need(struct btrfs_inode *inode, struct page **pages,
                                size_t num_pages, loff_t pos,
                                size_t write_bytes,
                                u64 *lockstart, u64 *lockend, bool nowait,
                                struct extent_state **cached_state)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        u64 start_pos;
        u64 last_pos;
        int i;
        int ret = 0;

        start_pos = round_down(pos, fs_info->sectorsize);
        last_pos = round_up(pos + write_bytes, fs_info->sectorsize) - 1;

        if (start_pos < inode->vfs_inode.i_size) {
                struct btrfs_ordered_extent *ordered;

                if (nowait) {
                        if (!try_lock_extent(&inode->io_tree, start_pos, last_pos,
                                             cached_state)) {
                                for (i = 0; i < num_pages; i++) {
                                        unlock_page(pages[i]);
                                        put_page(pages[i]);
                                        pages[i] = NULL;
                                }

                                return -EAGAIN;
                        }
                } else {
                        lock_extent(&inode->io_tree, start_pos, last_pos, cached_state);
                }

                ordered = btrfs_lookup_ordered_range(inode, start_pos,
                                                     last_pos - start_pos + 1);
                if (ordered &&
                    ordered->file_offset + ordered->num_bytes > start_pos &&
                    ordered->file_offset <= last_pos) {
                        unlock_extent(&inode->io_tree, start_pos, last_pos,
                                      cached_state);
                        for (i = 0; i < num_pages; i++) {
                                unlock_page(pages[i]);
                                put_page(pages[i]);
                        }
                        btrfs_start_ordered_extent(ordered);
                        btrfs_put_ordered_extent(ordered);
                        return -EAGAIN;
                }
                if (ordered)
                        btrfs_put_ordered_extent(ordered);

                *lockstart = start_pos;
                *lockend = last_pos;
                ret = 1;
        }

        /*
         * We should be called after prepare_pages() which should have locked
         * all pages in the range.
         */
        for (i = 0; i < num_pages; i++)
                WARN_ON(!PageLocked(pages[i]));

        return ret;
}

/*
 * Check if we can do nocow write into the range [@pos, @pos + @write_bytes)
 *
 * @pos:         File offset.
 * @write_bytes: The length to write, will be updated to the nocow writeable
 *               range.
 *
 * This function will flush ordered extents in the range to ensure proper
 * nocow checks.
 *
 * Return:
 * > 0          If we can nocow, and updates @write_bytes.
 *  0           If we can't do a nocow write.
 * -EAGAIN      If we can't do a nocow write because snapshoting of the inode's
 *              root is in progress.
 * < 0          If an error happened.
 *
 * NOTE: Callers need to call btrfs_check_nocow_unlock() if we return > 0.
 */
int btrfs_check_nocow_lock(struct btrfs_inode *inode, loff_t pos,
                           size_t *write_bytes, bool nowait)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct btrfs_root *root = inode->root;
        struct extent_state *cached_state = NULL;
        u64 lockstart, lockend;
        u64 num_bytes;
        int ret;

        if (!(inode->flags & (BTRFS_INODE_NODATACOW | BTRFS_INODE_PREALLOC)))
                return 0;

        if (!btrfs_drew_try_write_lock(&root->snapshot_lock))
                return -EAGAIN;

        lockstart = round_down(pos, fs_info->sectorsize);
        lockend = round_up(pos + *write_bytes,
                           fs_info->sectorsize) - 1;
        num_bytes = lockend - lockstart + 1;

        if (nowait) {
                if (!btrfs_try_lock_ordered_range(inode, lockstart, lockend,
                                                  &cached_state)) {
                        btrfs_drew_write_unlock(&root->snapshot_lock);
                        return -EAGAIN;
                }
        } else {
                btrfs_lock_and_flush_ordered_range(inode, lockstart, lockend,
                                                   &cached_state);
        }
        ret = can_nocow_extent(&inode->vfs_inode, lockstart, &num_bytes,
                        NULL, NULL, NULL, nowait, false);
        if (ret <= 0)
                btrfs_drew_write_unlock(&root->snapshot_lock);
        else
                *write_bytes = min_t(size_t, *write_bytes ,
                                     num_bytes - pos + lockstart);
        unlock_extent(&inode->io_tree, lockstart, lockend, &cached_state);

        return ret;
}

void btrfs_check_nocow_unlock(struct btrfs_inode *inode)
{
        btrfs_drew_write_unlock(&inode->root->snapshot_lock);
}

static void update_time_for_write(struct inode *inode)
{
        struct timespec64 now;

        if (IS_NOCMTIME(inode))
                return;

        now = current_time(inode);
        if (!timespec64_equal(&inode->i_mtime, &now))
                inode->i_mtime = now;

        if (!timespec64_equal(&inode->i_ctime, &now))
                inode->i_ctime = now;

        if (IS_I_VERSION(inode))
                inode_inc_iversion(inode);
}

static int btrfs_write_check(struct kiocb *iocb, struct iov_iter *from,
                             size_t count)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        loff_t pos = iocb->ki_pos;
        int ret;
        loff_t oldsize;
        loff_t start_pos;

        /*
         * Quickly bail out on NOWAIT writes if we don't have the nodatacow or
         * prealloc flags, as without those flags we always have to COW. We will
         * later check if we can really COW into the target range (using
         * can_nocow_extent() at btrfs_get_blocks_direct_write()).
         */
        if ((iocb->ki_flags & IOCB_NOWAIT) &&
            !(BTRFS_I(inode)->flags & (BTRFS_INODE_NODATACOW | BTRFS_INODE_PREALLOC)))
                return -EAGAIN;

        ret = file_remove_privs(file);
        if (ret)
                return ret;

        /*
         * We reserve space for updating the inode when we reserve space for the
         * extent we are going to write, so we will enospc out there.  We don't
         * need to start yet another transaction to update the inode as we will
         * update the inode when we finish writing whatever data we write.
         */
        update_time_for_write(inode);

        start_pos = round_down(pos, fs_info->sectorsize);
        oldsize = i_size_read(inode);
        if (start_pos > oldsize) {
                /* Expand hole size to cover write data, preventing empty gap */
                loff_t end_pos = round_up(pos + count, fs_info->sectorsize);

                ret = btrfs_cont_expand(BTRFS_I(inode), oldsize, end_pos);
                if (ret)
                        return ret;
        }

        return 0;
}

static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
                                               struct iov_iter *i)
{
        struct file *file = iocb->ki_filp;
        loff_t pos;
        struct inode *inode = file_inode(file);
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct page **pages = NULL;
        struct extent_changeset *data_reserved = NULL;
        u64 release_bytes = 0;
        u64 lockstart;
        u64 lockend;
        size_t num_written = 0;
        int nrptrs;
        ssize_t ret;
        bool only_release_metadata = false;
        bool force_page_uptodate = false;
        loff_t old_isize = i_size_read(inode);
        unsigned int ilock_flags = 0;
        const bool nowait = (iocb->ki_flags & IOCB_NOWAIT);
        unsigned int bdp_flags = (nowait ? BDP_ASYNC : 0);

        if (nowait)
                ilock_flags |= BTRFS_ILOCK_TRY;

        ret = btrfs_inode_lock(BTRFS_I(inode), ilock_flags);
        if (ret < 0)
                return ret;

        ret = generic_write_checks(iocb, i);
        if (ret <= 0)
                goto out;

        ret = btrfs_write_check(iocb, i, ret);
        if (ret < 0)
                goto out;

        pos = iocb->ki_pos;
        nrptrs = min(DIV_ROUND_UP(iov_iter_count(i), PAGE_SIZE),
                        PAGE_SIZE / (sizeof(struct page *)));
        nrptrs = min(nrptrs, current->nr_dirtied_pause - current->nr_dirtied);
        nrptrs = max(nrptrs, 8);
        pages = kmalloc_array(nrptrs, sizeof(struct page *), GFP_KERNEL);
        if (!pages) {
                ret = -ENOMEM;
                goto out;
        }

        while (iov_iter_count(i) > 0) {
                struct extent_state *cached_state = NULL;
                size_t offset = offset_in_page(pos);
                size_t sector_offset;
                size_t write_bytes = min(iov_iter_count(i),
                                         nrptrs * (size_t)PAGE_SIZE -
                                         offset);
                size_t num_pages;
                size_t reserve_bytes;
                size_t dirty_pages;
                size_t copied;
                size_t dirty_sectors;
                size_t num_sectors;
                int extents_locked;

                /*
                 * Fault pages before locking them in prepare_pages
                 * to avoid recursive lock
                 */
                if (unlikely(fault_in_iov_iter_readable(i, write_bytes))) {
                        ret = -EFAULT;
                        break;
                }

                only_release_metadata = false;
                sector_offset = pos & (fs_info->sectorsize - 1);

                extent_changeset_release(data_reserved);
                ret = btrfs_check_data_free_space(BTRFS_I(inode),
                                                  &data_reserved, pos,
                                                  write_bytes, nowait);
                if (ret < 0) {
                        int can_nocow;

                        if (nowait && (ret == -ENOSPC || ret == -EAGAIN)) {
                                ret = -EAGAIN;
                                break;
                        }

                        /*
                         * If we don't have to COW at the offset, reserve
                         * metadata only. write_bytes may get smaller than
                         * requested here.
                         */
                        can_nocow = btrfs_check_nocow_lock(BTRFS_I(inode), pos,
                                                           &write_bytes, nowait);
                        if (can_nocow < 0)
                                ret = can_nocow;
                        if (can_nocow > 0)
                                ret = 0;
                        if (ret)
                                break;
                        only_release_metadata = true;
                }

                num_pages = DIV_ROUND_UP(write_bytes + offset, PAGE_SIZE);
                WARN_ON(num_pages > nrptrs);
                reserve_bytes = round_up(write_bytes + sector_offset,
                                         fs_info->sectorsize);
                WARN_ON(reserve_bytes == 0);
                ret = btrfs_delalloc_reserve_metadata(BTRFS_I(inode),
                                                      reserve_bytes,
                                                      reserve_bytes, nowait);
                if (ret) {
                        if (!only_release_metadata)
                                btrfs_free_reserved_data_space(BTRFS_I(inode),
                                                data_reserved, pos,
                                                write_bytes);
                        else
                                btrfs_check_nocow_unlock(BTRFS_I(inode));

                        if (nowait && ret == -ENOSPC)
                                ret = -EAGAIN;
                        break;
                }

                release_bytes = reserve_bytes;
again:
                ret = balance_dirty_pages_ratelimited_flags(inode->i_mapping, bdp_flags);
                if (ret) {
                        btrfs_delalloc_release_extents(BTRFS_I(inode), reserve_bytes);
                        break;
                }

                /*
                 * This is going to setup the pages array with the number of
                 * pages we want, so we don't really need to worry about the
                 * contents of pages from loop to loop
                 */
                ret = prepare_pages(inode, pages, num_pages,
                                    pos, write_bytes, force_page_uptodate, false);
                if (ret) {
                        btrfs_delalloc_release_extents(BTRFS_I(inode),
                                                       reserve_bytes);
                        break;
                }

                extents_locked = lock_and_cleanup_extent_if_need(
                                BTRFS_I(inode), pages,
                                num_pages, pos, write_bytes, &lockstart,
                                &lockend, nowait, &cached_state);
                if (extents_locked < 0) {
                        if (!nowait && extents_locked == -EAGAIN)
                                goto again;

                        btrfs_delalloc_release_extents(BTRFS_I(inode),
                                                       reserve_bytes);
                        ret = extents_locked;
                        break;
                }

                copied = btrfs_copy_from_user(pos, write_bytes, pages, i);

                num_sectors = BTRFS_BYTES_TO_BLKS(fs_info, reserve_bytes);
                dirty_sectors = round_up(copied + sector_offset,
                                        fs_info->sectorsize);
                dirty_sectors = BTRFS_BYTES_TO_BLKS(fs_info, dirty_sectors);

                /*
                 * if we have trouble faulting in the pages, fall
                 * back to one page at a time
                 */
                if (copied < write_bytes)
                        nrptrs = 1;

                if (copied == 0) {
                        force_page_uptodate = true;
                        dirty_sectors = 0;
                        dirty_pages = 0;
                } else {
                        force_page_uptodate = false;
                        dirty_pages = DIV_ROUND_UP(copied + offset,
                                                   PAGE_SIZE);
                }

                if (num_sectors > dirty_sectors) {
                        /* release everything except the sectors we dirtied */
                        release_bytes -= dirty_sectors << fs_info->sectorsize_bits;
                        if (only_release_metadata) {
                                btrfs_delalloc_release_metadata(BTRFS_I(inode),
                                                        release_bytes, true);
                        } else {
                                u64 __pos;

                                __pos = round_down(pos,
                                                   fs_info->sectorsize) +
                                        (dirty_pages << PAGE_SHIFT);
                                btrfs_delalloc_release_space(BTRFS_I(inode),
                                                data_reserved, __pos,
                                                release_bytes, true);
                        }
                }

                release_bytes = round_up(copied + sector_offset,
                                        fs_info->sectorsize);

                ret = btrfs_dirty_pages(BTRFS_I(inode), pages,
                                        dirty_pages, pos, copied,
                                        &cached_state, only_release_metadata);

                /*
                 * If we have not locked the extent range, because the range's
                 * start offset is >= i_size, we might still have a non-NULL
                 * cached extent state, acquired while marking the extent range
                 * as delalloc through btrfs_dirty_pages(). Therefore free any
                 * possible cached extent state to avoid a memory leak.
                 */
                if (extents_locked)
                        unlock_extent(&BTRFS_I(inode)->io_tree, lockstart,
                                      lockend, &cached_state);
                else
                        free_extent_state(cached_state);

                btrfs_delalloc_release_extents(BTRFS_I(inode), reserve_bytes);
                if (ret) {
                        btrfs_drop_pages(fs_info, pages, num_pages, pos, copied);
                        break;
                }

                release_bytes = 0;
                if (only_release_metadata)
                        btrfs_check_nocow_unlock(BTRFS_I(inode));

                btrfs_drop_pages(fs_info, pages, num_pages, pos, copied);

                cond_resched();

                pos += copied;
                num_written += copied;
        }

        kfree(pages);

        if (release_bytes) {
                if (only_release_metadata) {
                        btrfs_check_nocow_unlock(BTRFS_I(inode));
                        btrfs_delalloc_release_metadata(BTRFS_I(inode),
                                        release_bytes, true);
                } else {
                        btrfs_delalloc_release_space(BTRFS_I(inode),
                                        data_reserved,
                                        round_down(pos, fs_info->sectorsize),
                                        release_bytes, true);
                }
        }

        extent_changeset_free(data_reserved);
        if (num_written > 0) {
                pagecache_isize_extended(inode, old_isize, iocb->ki_pos);
                iocb->ki_pos += num_written;
        }
out:
        btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
        return num_written ? num_written : ret;
}

static ssize_t check_direct_IO(struct btrfs_fs_info *fs_info,
                               const struct iov_iter *iter, loff_t offset)
{
        const u32 blocksize_mask = fs_info->sectorsize - 1;

        if (offset & blocksize_mask)
                return -EINVAL;

        if (iov_iter_alignment(iter) & blocksize_mask)
                return -EINVAL;

        return 0;
}

static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        loff_t pos;
        ssize_t written = 0;
        ssize_t written_buffered;
        size_t prev_left = 0;
        loff_t endbyte;
        ssize_t err;
        unsigned int ilock_flags = 0;
        struct iomap_dio *dio;

        if (iocb->ki_flags & IOCB_NOWAIT)
                ilock_flags |= BTRFS_ILOCK_TRY;

        /* If the write DIO is within EOF, use a shared lock */
        if (iocb->ki_pos + iov_iter_count(from) <= i_size_read(inode))
                ilock_flags |= BTRFS_ILOCK_SHARED;

relock:
        err = btrfs_inode_lock(BTRFS_I(inode), ilock_flags);
        if (err < 0)
                return err;

        err = generic_write_checks(iocb, from);
        if (err <= 0) {
                btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
                return err;
        }

        err = btrfs_write_check(iocb, from, err);
        if (err < 0) {
                btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
                goto out;
        }

        pos = iocb->ki_pos;
        /*
         * Re-check since file size may have changed just before taking the
         * lock or pos may have changed because of O_APPEND in generic_write_check()
         */
        if ((ilock_flags & BTRFS_ILOCK_SHARED) &&
            pos + iov_iter_count(from) > i_size_read(inode)) {
                btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
                ilock_flags &= ~BTRFS_ILOCK_SHARED;
                goto relock;
        }

        if (check_direct_IO(fs_info, from, pos)) {
                btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
                goto buffered;
        }

        /*
         * The iov_iter can be mapped to the same file range we are writing to.
         * If that's the case, then we will deadlock in the iomap code, because
         * it first calls our callback btrfs_dio_iomap_begin(), which will create
         * an ordered extent, and after that it will fault in the pages that the
         * iov_iter refers to. During the fault in we end up in the readahead
         * pages code (starting at btrfs_readahead()), which will lock the range,
         * find that ordered extent and then wait for it to complete (at
         * btrfs_lock_and_flush_ordered_range()), resulting in a deadlock since
         * obviously the ordered extent can never complete as we didn't submit
         * yet the respective bio(s). This always happens when the buffer is
         * memory mapped to the same file range, since the iomap DIO code always
         * invalidates pages in the target file range (after starting and waiting
         * for any writeback).
         *
         * So here we disable page faults in the iov_iter and then retry if we
         * got -EFAULT, faulting in the pages before the retry.
         */
        from->nofault = true;
        dio = btrfs_dio_write(iocb, from, written);
        from->nofault = false;

        /*
         * iomap_dio_complete() will call btrfs_sync_file() if we have a dsync
         * iocb, and that needs to lock the inode. So unlock it before calling
         * iomap_dio_complete() to avoid a deadlock.
         */
        btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);

        if (IS_ERR_OR_NULL(dio))
                err = PTR_ERR_OR_ZERO(dio);
        else
                err = iomap_dio_complete(dio);

        /* No increment (+=) because iomap returns a cumulative value. */
        if (err > 0)
                written = err;

        if (iov_iter_count(from) > 0 && (err == -EFAULT || err > 0)) {
                const size_t left = iov_iter_count(from);
                /*
                 * We have more data left to write. Try to fault in as many as
                 * possible of the remainder pages and retry. We do this without
                 * releasing and locking again the inode, to prevent races with
                 * truncate.
                 *
                 * Also, in case the iov refers to pages in the file range of the
                 * file we want to write to (due to a mmap), we could enter an
                 * infinite loop if we retry after faulting the pages in, since
                 * iomap will invalidate any pages in the range early on, before
                 * it tries to fault in the pages of the iov. So we keep track of
                 * how much was left of iov in the previous EFAULT and fallback
                 * to buffered IO in case we haven't made any progress.
                 */
                if (left == prev_left) {
                        err = -ENOTBLK;
                } else {
                        fault_in_iov_iter_readable(from, left);
                        prev_left = left;
                        goto relock;
                }
        }

        /*
         * If 'err' is -ENOTBLK or we have not written all data, then it means
         * we must fallback to buffered IO.
         */
        if ((err < 0 && err != -ENOTBLK) || !iov_iter_count(from))
                goto out;

buffered:
        /*
         * If we are in a NOWAIT context, then return -EAGAIN to signal the caller
         * it must retry the operation in a context where blocking is acceptable,
         * because even if we end up not blocking during the buffered IO attempt
         * below, we will block when flushing and waiting for the IO.
         */
        if (iocb->ki_flags & IOCB_NOWAIT) {
                err = -EAGAIN;
                goto out;
        }

        pos = iocb->ki_pos;
        written_buffered = btrfs_buffered_write(iocb, from);
        if (written_buffered < 0) {
                err = written_buffered;
                goto out;
        }
        /*
         * Ensure all data is persisted. We want the next direct IO read to be
         * able to read what was just written.
         */
        endbyte = pos + written_buffered - 1;
        err = btrfs_fdatawrite_range(inode, pos, endbyte);
        if (err)
                goto out;
        err = filemap_fdatawait_range(inode->i_mapping, pos, endbyte);
        if (err)
                goto out;
        written += written_buffered;
        iocb->ki_pos = pos + written_buffered;
        invalidate_mapping_pages(file->f_mapping, pos >> PAGE_SHIFT,
                                 endbyte >> PAGE_SHIFT);
out:
        return err < 0 ? err : written;
}

static ssize_t btrfs_encoded_write(struct kiocb *iocb, struct iov_iter *from,
                        const struct btrfs_ioctl_encoded_io_args *encoded)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        loff_t count;
        ssize_t ret;

        btrfs_inode_lock(BTRFS_I(inode), 0);
        count = encoded->len;
        ret = generic_write_checks_count(iocb, &count);
        if (ret == 0 && count != encoded->len) {
                /*
                 * The write got truncated by generic_write_checks_count(). We
                 * can't do a partial encoded write.
                 */
                ret = -EFBIG;
        }
        if (ret || encoded->len == 0)
                goto out;

        ret = btrfs_write_check(iocb, from, encoded->len);
        if (ret < 0)
                goto out;

        ret = btrfs_do_encoded_write(iocb, from, encoded);
out:
        btrfs_inode_unlock(BTRFS_I(inode), 0);
        return ret;
}

ssize_t btrfs_do_write_iter(struct kiocb *iocb, struct iov_iter *from,
                            const struct btrfs_ioctl_encoded_io_args *encoded)
{
        struct file *file = iocb->ki_filp;
        struct btrfs_inode *inode = BTRFS_I(file_inode(file));
        ssize_t num_written, num_sync;

        /*
         * If the fs flips readonly due to some impossible error, although we
         * have opened a file as writable, we have to stop this write operation
         * to ensure consistency.
         */
        if (BTRFS_FS_ERROR(inode->root->fs_info))
                return -EROFS;

        if (encoded && (iocb->ki_flags & IOCB_NOWAIT))
                return -EOPNOTSUPP;

        if (encoded) {
                num_written = btrfs_encoded_write(iocb, from, encoded);
                num_sync = encoded->len;
        } else if (iocb->ki_flags & IOCB_DIRECT) {
                num_written = btrfs_direct_write(iocb, from);
                num_sync = num_written;
        } else {
                num_written = btrfs_buffered_write(iocb, from);
                num_sync = num_written;
        }

        btrfs_set_inode_last_sub_trans(inode);

        if (num_sync > 0) {
                num_sync = generic_write_sync(iocb, num_sync);
                if (num_sync < 0)
                        num_written = num_sync;
        }

        return num_written;
}

static ssize_t btrfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
        return btrfs_do_write_iter(iocb, from, NULL);
}

int btrfs_release_file(struct inode *inode, struct file *filp)
{
        struct btrfs_file_private *private = filp->private_data;

        if (private) {
                kfree(private->filldir_buf);
                free_extent_state(private->llseek_cached_state);
                kfree(private);
                filp->private_data = NULL;
        }

        /*
         * Set by setattr when we are about to truncate a file from a non-zero
         * size to a zero size.  This tries to flush down new bytes that may
         * have been written if the application were using truncate to replace
         * a file in place.
         */
        if (test_and_clear_bit(BTRFS_INODE_FLUSH_ON_CLOSE,
                               &BTRFS_I(inode)->runtime_flags))
                        filemap_flush(inode->i_mapping);
        return 0;
}

static int start_ordered_ops(struct inode *inode, loff_t start, loff_t end)
{
        int ret;
        struct blk_plug plug;

        /*
         * This is only called in fsync, which would do synchronous writes, so
         * a plug can merge adjacent IOs as much as possible.  Esp. in case of
         * multiple disks using raid profile, a large IO can be split to
         * several segments of stripe length (currently 64K).
         */
        blk_start_plug(&plug);
        ret = btrfs_fdatawrite_range(inode, start, end);
        blk_finish_plug(&plug);

        return ret;
}

static inline bool skip_inode_logging(const struct btrfs_log_ctx *ctx)
{
        struct btrfs_inode *inode = BTRFS_I(ctx->inode);
        struct btrfs_fs_info *fs_info = inode->root->fs_info;

        if (btrfs_inode_in_log(inode, fs_info->generation) &&
            list_empty(&ctx->ordered_extents))
                return true;

        /*
         * If we are doing a fast fsync we can not bail out if the inode's
         * last_trans is <= then the last committed transaction, because we only
         * update the last_trans of the inode during ordered extent completion,
         * and for a fast fsync we don't wait for that, we only wait for the
         * writeback to complete.
         */
        if (inode->last_trans <= fs_info->last_trans_committed &&
            (test_bit(BTRFS_INODE_NEEDS_FULL_SYNC, &inode->runtime_flags) ||
             list_empty(&ctx->ordered_extents)))
                return true;

        return false;
}

/*
 * fsync call for both files and directories.  This logs the inode into
 * the tree log instead of forcing full commits whenever possible.
 *
 * It needs to call filemap_fdatawait so that all ordered extent updates are
 * in the metadata btree are up to date for copying to the log.
 *
 * It drops the inode mutex before doing the tree log commit.  This is an
 * important optimization for directories because holding the mutex prevents
 * new operations on the dir while we write to disk.
 */
int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
{
        struct dentry *dentry = file_dentry(file);
        struct inode *inode = d_inode(dentry);
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_trans_handle *trans;
        struct btrfs_log_ctx ctx;
        int ret = 0, err;
        u64 len;
        bool full_sync;

        trace_btrfs_sync_file(file, datasync);

        btrfs_init_log_ctx(&ctx, inode);

        /*
         * Always set the range to a full range, otherwise we can get into
         * several problems, from missing file extent items to represent holes
         * when not using the NO_HOLES feature, to log tree corruption due to
         * races between hole detection during logging and completion of ordered
         * extents outside the range, to missing checksums due to ordered extents
         * for which we flushed only a subset of their pages.
         */
        start = 0;
        end = LLONG_MAX;
        len = (u64)LLONG_MAX + 1;

        /*
         * We write the dirty pages in the range and wait until they complete
         * out of the ->i_mutex. If so, we can flush the dirty pages by
         * multi-task, and make the performance up.  See
         * btrfs_wait_ordered_range for an explanation of the ASYNC check.
         */
        ret = start_ordered_ops(inode, start, end);
        if (ret)
                goto out;

        btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);

        atomic_inc(&root->log_batch);

        /*
         * Before we acquired the inode's lock and the mmap lock, someone may
         * have dirtied more pages in the target range. We need to make sure
         * that writeback for any such pages does not start while we are logging
         * the inode, because if it does, any of the following might happen when
         * we are not doing a full inode sync:
         *
         * 1) We log an extent after its writeback finishes but before its
         *    checksums are added to the csum tree, leading to -EIO errors
         *    when attempting to read the extent after a log replay.
         *
         * 2) We can end up logging an extent before its writeback finishes.
         *    Therefore after the log replay we will have a file extent item
         *    pointing to an unwritten extent (and no data checksums as well).
         *
         * So trigger writeback for any eventual new dirty pages and then we
         * wait for all ordered extents to complete below.
         */
        ret = start_ordered_ops(inode, start, end);
        if (ret) {
                btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
                goto out;
        }

        /*
         * Always check for the full sync flag while holding the inode's lock,
         * to avoid races with other tasks. The flag must be either set all the
         * time during logging or always off all the time while logging.
         * We check the flag here after starting delalloc above, because when
         * running delalloc the full sync flag may be set if we need to drop
         * extra extent map ranges due to temporary memory allocation failures.
         */
        full_sync = test_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
                             &BTRFS_I(inode)->runtime_flags);

        /*
         * We have to do this here to avoid the priority inversion of waiting on
         * IO of a lower priority task while holding a transaction open.
         *
         * For a full fsync we wait for the ordered extents to complete while
         * for a fast fsync we wait just for writeback to complete, and then
         * attach the ordered extents to the transaction so that a transaction
         * commit waits for their completion, to avoid data loss if we fsync,
         * the current transaction commits before the ordered extents complete
         * and a power failure happens right after that.
         *
         * For zoned filesystem, if a write IO uses a ZONE_APPEND command, the
         * logical address recorded in the ordered extent may change. We need
         * to wait for the IO to stabilize the logical address.
         */
        if (full_sync || btrfs_is_zoned(fs_info)) {
                ret = btrfs_wait_ordered_range(inode, start, len);
        } else {
                /*
                 * Get our ordered extents as soon as possible to avoid doing
                 * checksum lookups in the csum tree, and use instead the
                 * checksums attached to the ordered extents.
                 */
                btrfs_get_ordered_extents_for_logging(BTRFS_I(inode),
                                                      &ctx.ordered_extents);
                ret = filemap_fdatawait_range(inode->i_mapping, start, end);
        }

        if (ret)
                goto out_release_extents;

        atomic_inc(&root->log_batch);

        smp_mb();
        if (skip_inode_logging(&ctx)) {
                /*
                 * We've had everything committed since the last time we were
                 * modified so clear this flag in case it was set for whatever
                 * reason, it's no longer relevant.
                 */
                clear_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
                          &BTRFS_I(inode)->runtime_flags);
                /*
                 * An ordered extent might have started before and completed
                 * already with io errors, in which case the inode was not
                 * updated and we end up here. So check the inode's mapping
                 * for any errors that might have happened since we last
                 * checked called fsync.
                 */
                ret = filemap_check_wb_err(inode->i_mapping, file->f_wb_err);
                goto out_release_extents;
        }

        /*
         * We use start here because we will need to wait on the IO to complete
         * in btrfs_sync_log, which could require joining a transaction (for
         * example checking cross references in the nocow path).  If we use join
         * here we could get into a situation where we're waiting on IO to
         * happen that is blocked on a transaction trying to commit.  With start
         * we inc the extwriter counter, so we wait for all extwriters to exit
         * before we start blocking joiners.  This comment is to keep somebody
         * from thinking they are super smart and changing this to
         * btrfs_join_transaction *cough*Josef*cough*.
         */
        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                goto out_release_extents;
        }
        trans->in_fsync = true;

        ret = btrfs_log_dentry_safe(trans, dentry, &ctx);
        btrfs_release_log_ctx_extents(&ctx);
        if (ret < 0) {
                /* Fallthrough and commit/free transaction. */
                ret = BTRFS_LOG_FORCE_COMMIT;
        }

        /* we've logged all the items and now have a consistent
         * version of the file in the log.  It is possible that
         * someone will come in and modify the file, but that's
         * fine because the log is consistent on disk, and we
         * have references to all of the file's extents
         *
         * It is possible that someone will come in and log the
         * file again, but that will end up using the synchronization
         * inside btrfs_sync_log to keep things safe.
         */
        btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);

        if (ret == BTRFS_NO_LOG_SYNC) {
                ret = btrfs_end_transaction(trans);
                goto out;
        }

        /* We successfully logged the inode, attempt to sync the log. */
        if (!ret) {
                ret = btrfs_sync_log(trans, root, &ctx);
                if (!ret) {
                        ret = btrfs_end_transaction(trans);
                        goto out;
                }
        }

        /*
         * At this point we need to commit the transaction because we had
         * btrfs_need_log_full_commit() or some other error.
         *
         * If we didn't do a full sync we have to stop the trans handle, wait on
         * the ordered extents, start it again and commit the transaction.  If
         * we attempt to wait on the ordered extents here we could deadlock with
         * something like fallocate() that is holding the extent lock trying to
         * start a transaction while some other thread is trying to commit the
         * transaction while we (fsync) are currently holding the transaction
         * open.
         */
        if (!full_sync) {
                ret = btrfs_end_transaction(trans);
                if (ret)
                        goto out;
                ret = btrfs_wait_ordered_range(inode, start, len);
                if (ret)
                        goto out;

                /*
                 * This is safe to use here because we're only interested in
                 * making sure the transaction that had the ordered extents is
                 * committed.  We aren't waiting on anything past this point,
                 * we're purely getting the transaction and committing it.
                 */
                trans = btrfs_attach_transaction_barrier(root);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);

                        /*
                         * We committed the transaction and there's no currently
                         * running transaction, this means everything we care
                         * about made it to disk and we are done.
                         */
                        if (ret == -ENOENT)
                                ret = 0;
                        goto out;
                }
        }

        ret = btrfs_commit_transaction(trans);
out:
        ASSERT(list_empty(&ctx.list));
        ASSERT(list_empty(&ctx.conflict_inodes));
        err = file_check_and_advance_wb_err(file);
        if (!ret)
                ret = err;
        return ret > 0 ? -EIO : ret;

out_release_extents:
        btrfs_release_log_ctx_extents(&ctx);
        btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
        goto out;
}

static const struct vm_operations_struct btrfs_file_vm_ops = {
        .fault          = filemap_fault,
        .map_pages      = filemap_map_pages,
        .page_mkwrite   = btrfs_page_mkwrite,
};

static int btrfs_file_mmap(struct file  *filp, struct vm_area_struct *vma)
{
        struct address_space *mapping = filp->f_mapping;

        if (!mapping->a_ops->read_folio)
                return -ENOEXEC;

        file_accessed(filp);
        vma->vm_ops = &btrfs_file_vm_ops;

        return 0;
}

static int hole_mergeable(struct btrfs_inode *inode, struct extent_buffer *leaf,
                          int slot, u64 start, u64 end)
{
        struct btrfs_file_extent_item *fi;
        struct btrfs_key key;

        if (slot < 0 || slot >= btrfs_header_nritems(leaf))
                return 0;

        btrfs_item_key_to_cpu(leaf, &key, slot);
        if (key.objectid != btrfs_ino(inode) ||
            key.type != BTRFS_EXTENT_DATA_KEY)
                return 0;

        fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);

        if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_REG)
                return 0;

        if (btrfs_file_extent_disk_bytenr(leaf, fi))
                return 0;

        if (key.offset == end)
                return 1;
        if (key.offset + btrfs_file_extent_num_bytes(leaf, fi) == start)
                return 1;
        return 0;
}

static int fill_holes(struct btrfs_trans_handle *trans,
                struct btrfs_inode *inode,
                struct btrfs_path *path, u64 offset, u64 end)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root = inode->root;
        struct extent_buffer *leaf;
        struct btrfs_file_extent_item *fi;
        struct extent_map *hole_em;
        struct btrfs_key key;
        int ret;

        if (btrfs_fs_incompat(fs_info, NO_HOLES))
                goto out;

        key.objectid = btrfs_ino(inode);
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = offset;

        ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
        if (ret <= 0) {
                /*
                 * We should have dropped this offset, so if we find it then
                 * something has gone horribly wrong.
                 */
                if (ret == 0)
                        ret = -EINVAL;
                return ret;
        }

        leaf = path->nodes[0];
        if (hole_mergeable(inode, leaf, path->slots[0] - 1, offset, end)) {
                u64 num_bytes;

                path->slots[0]--;
                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                num_bytes = btrfs_file_extent_num_bytes(leaf, fi) +
                        end - offset;
                btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_ram_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_offset(leaf, fi, 0);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_mark_buffer_dirty(leaf);
                goto out;
        }

        if (hole_mergeable(inode, leaf, path->slots[0], offset, end)) {
                u64 num_bytes;

                key.offset = offset;
                btrfs_set_item_key_safe(fs_info, path, &key);
                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                num_bytes = btrfs_file_extent_num_bytes(leaf, fi) + end -
                        offset;
                btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_ram_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_offset(leaf, fi, 0);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_mark_buffer_dirty(leaf);
                goto out;
        }
        btrfs_release_path(path);

        ret = btrfs_insert_hole_extent(trans, root, btrfs_ino(inode), offset,
                                       end - offset);
        if (ret)
                return ret;

out:
        btrfs_release_path(path);

        hole_em = alloc_extent_map();
        if (!hole_em) {
                btrfs_drop_extent_map_range(inode, offset, end - 1, false);
                btrfs_set_inode_full_sync(inode);
        } else {
                hole_em->start = offset;
                hole_em->len = end - offset;
                hole_em->ram_bytes = hole_em->len;
                hole_em->orig_start = offset;

                hole_em->block_start = EXTENT_MAP_HOLE;
                hole_em->block_len = 0;
                hole_em->orig_block_len = 0;
                hole_em->compress_type = BTRFS_COMPRESS_NONE;
                hole_em->generation = trans->transid;

                ret = btrfs_replace_extent_map_range(inode, hole_em, true);
                free_extent_map(hole_em);
                if (ret)
                        btrfs_set_inode_full_sync(inode);
        }

        return 0;
}

/*
 * Find a hole extent on given inode and change start/len to the end of hole
 * extent.(hole/vacuum extent whose em->start <= start &&
 *         em->start + em->len > start)
 * When a hole extent is found, return 1 and modify start/len.
 */
static int find_first_non_hole(struct btrfs_inode *inode, u64 *start, u64 *len)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct extent_map *em;
        int ret = 0;

        em = btrfs_get_extent(inode, NULL, 0,
                              round_down(*start, fs_info->sectorsize),
                              round_up(*len, fs_info->sectorsize));
        if (IS_ERR(em))
                return PTR_ERR(em);

        /* Hole or vacuum extent(only exists in no-hole mode) */
        if (em->block_start == EXTENT_MAP_HOLE) {
                ret = 1;
                *len = em->start + em->len > *start + *len ?
                       0 : *start + *len - em->start - em->len;
                *start = em->start + em->len;
        }
        free_extent_map(em);
        return ret;
}

static void btrfs_punch_hole_lock_range(struct inode *inode,
                                        const u64 lockstart,
                                        const u64 lockend,
                                        struct extent_state **cached_state)
{
        /*
         * For subpage case, if the range is not at page boundary, we could
         * have pages at the leading/tailing part of the range.
         * This could lead to dead loop since filemap_range_has_page()
         * will always return true.
         * So here we need to do extra page alignment for
         * filemap_range_has_page().
         */
        const u64 page_lockstart = round_up(lockstart, PAGE_SIZE);
        const u64 page_lockend = round_down(lockend + 1, PAGE_SIZE) - 1;

        while (1) {
                truncate_pagecache_range(inode, lockstart, lockend);

                lock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                            cached_state);
                /*
                 * We can't have ordered extents in the range, nor dirty/writeback
                 * pages, because we have locked the inode's VFS lock in exclusive
                 * mode, we have locked the inode's i_mmap_lock in exclusive mode,
                 * we have flushed all delalloc in the range and we have waited
                 * for any ordered extents in the range to complete.
                 * We can race with anyone reading pages from this range, so after
                 * locking the range check if we have pages in the range, and if
                 * we do, unlock the range and retry.
                 */
                if (!filemap_range_has_page(inode->i_mapping, page_lockstart,
                                            page_lockend))
                        break;

                unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                              cached_state);
        }

        btrfs_assert_inode_range_clean(BTRFS_I(inode), lockstart, lockend);
}

static int btrfs_insert_replace_extent(struct btrfs_trans_handle *trans,
                                     struct btrfs_inode *inode,
                                     struct btrfs_path *path,
                                     struct btrfs_replace_extent_info *extent_info,
                                     const u64 replace_len,
                                     const u64 bytes_to_drop)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root = inode->root;
        struct btrfs_file_extent_item *extent;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        int slot;
        struct btrfs_ref ref = { 0 };
        int ret;

        if (replace_len == 0)
                return 0;

        if (extent_info->disk_offset == 0 &&
            btrfs_fs_incompat(fs_info, NO_HOLES)) {
                btrfs_update_inode_bytes(inode, 0, bytes_to_drop);
                return 0;
        }

        key.objectid = btrfs_ino(inode);
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = extent_info->file_offset;
        ret = btrfs_insert_empty_item(trans, root, path, &key,
                                      sizeof(struct btrfs_file_extent_item));
        if (ret)
                return ret;
        leaf = path->nodes[0];
        slot = path->slots[0];
        write_extent_buffer(leaf, extent_info->extent_buf,
                            btrfs_item_ptr_offset(leaf, slot),
                            sizeof(struct btrfs_file_extent_item));
        extent = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
        ASSERT(btrfs_file_extent_type(leaf, extent) != BTRFS_FILE_EXTENT_INLINE);
        btrfs_set_file_extent_offset(leaf, extent, extent_info->data_offset);
        btrfs_set_file_extent_num_bytes(leaf, extent, replace_len);
        if (extent_info->is_new_extent)
                btrfs_set_file_extent_generation(leaf, extent, trans->transid);
        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

        ret = btrfs_inode_set_file_extent_range(inode, extent_info->file_offset,
                                                replace_len);
        if (ret)
                return ret;

        /* If it's a hole, nothing more needs to be done. */
        if (extent_info->disk_offset == 0) {
                btrfs_update_inode_bytes(inode, 0, bytes_to_drop);
                return 0;
        }

        btrfs_update_inode_bytes(inode, replace_len, bytes_to_drop);

        if (extent_info->is_new_extent && extent_info->insertions == 0) {
                key.objectid = extent_info->disk_offset;
                key.type = BTRFS_EXTENT_ITEM_KEY;
                key.offset = extent_info->disk_len;
                ret = btrfs_alloc_reserved_file_extent(trans, root,
                                                       btrfs_ino(inode),
                                                       extent_info->file_offset,
                                                       extent_info->qgroup_reserved,
                                                       &key);
        } else {
                u64 ref_offset;

                btrfs_init_generic_ref(&ref, BTRFS_ADD_DELAYED_REF,
                                       extent_info->disk_offset,
                                       extent_info->disk_len, 0);
                ref_offset = extent_info->file_offset - extent_info->data_offset;
                btrfs_init_data_ref(&ref, root->root_key.objectid,
                                    btrfs_ino(inode), ref_offset, 0, false);
                ret = btrfs_inc_extent_ref(trans, &ref);
        }

        extent_info->insertions++;

        return ret;
}

/*
 * The respective range must have been previously locked, as well as the inode.
 * The end offset is inclusive (last byte of the range).
 * @extent_info is NULL for fallocate's hole punching and non-NULL when replacing
 * the file range with an extent.
 * When not punching a hole, we don't want to end up in a state where we dropped
 * extents without inserting a new one, so we must abort the transaction to avoid
 * a corruption.
 */
int btrfs_replace_file_extents(struct btrfs_inode *inode,
                               struct btrfs_path *path, const u64 start,
                               const u64 end,
                               struct btrfs_replace_extent_info *extent_info,
                               struct btrfs_trans_handle **trans_out)
{
        struct btrfs_drop_extents_args drop_args = { 0 };
        struct btrfs_root *root = inode->root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 min_size = btrfs_calc_insert_metadata_size(fs_info, 1);
        u64 ino_size = round_up(inode->vfs_inode.i_size, fs_info->sectorsize);
        struct btrfs_trans_handle *trans = NULL;
        struct btrfs_block_rsv *rsv;
        unsigned int rsv_count;
        u64 cur_offset;
        u64 len = end - start;
        int ret = 0;

        if (end <= start)
                return -EINVAL;

        rsv = btrfs_alloc_block_rsv(fs_info, BTRFS_BLOCK_RSV_TEMP);
        if (!rsv) {
                ret = -ENOMEM;
                goto out;
        }
        rsv->size = btrfs_calc_insert_metadata_size(fs_info, 1);
        rsv->failfast = true;

        /*
         * 1 - update the inode
         * 1 - removing the extents in the range
         * 1 - adding the hole extent if no_holes isn't set or if we are
         *     replacing the range with a new extent
         */
        if (!btrfs_fs_incompat(fs_info, NO_HOLES) || extent_info)
                rsv_count = 3;
        else
                rsv_count = 2;

        trans = btrfs_start_transaction(root, rsv_count);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                trans = NULL;
                goto out_free;
        }

        ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, rsv,
                                      min_size, false);
        if (WARN_ON(ret))
                goto out_trans;
        trans->block_rsv = rsv;

        cur_offset = start;
        drop_args.path = path;
        drop_args.end = end + 1;
        drop_args.drop_cache = true;
        while (cur_offset < end) {
                drop_args.start = cur_offset;
                ret = btrfs_drop_extents(trans, root, inode, &drop_args);
                /* If we are punching a hole decrement the inode's byte count */
                if (!extent_info)
                        btrfs_update_inode_bytes(inode, 0,
                                                 drop_args.bytes_found);
                if (ret != -ENOSPC) {
                        /*
                         * The only time we don't want to abort is if we are
                         * attempting to clone a partial inline extent, in which
                         * case we'll get EOPNOTSUPP.  However if we aren't
                         * clone we need to abort no matter what, because if we
                         * got EOPNOTSUPP via prealloc then we messed up and
                         * need to abort.
                         */
                        if (ret &&
                            (ret != -EOPNOTSUPP ||
                             (extent_info && extent_info->is_new_extent)))
                                btrfs_abort_transaction(trans, ret);
                        break;
                }

                trans->block_rsv = &fs_info->trans_block_rsv;

                if (!extent_info && cur_offset < drop_args.drop_end &&
                    cur_offset < ino_size) {
                        ret = fill_holes(trans, inode, path, cur_offset,
                                         drop_args.drop_end);
                        if (ret) {
                                /*
                                 * If we failed then we didn't insert our hole
                                 * entries for the area we dropped, so now the
                                 * fs is corrupted, so we must abort the
                                 * transaction.
                                 */
                                btrfs_abort_transaction(trans, ret);
                                break;
                        }
                } else if (!extent_info && cur_offset < drop_args.drop_end) {
                        /*
                         * We are past the i_size here, but since we didn't
                         * insert holes we need to clear the mapped area so we
                         * know to not set disk_i_size in this area until a new
                         * file extent is inserted here.
                         */
                        ret = btrfs_inode_clear_file_extent_range(inode,
                                        cur_offset,
                                        drop_args.drop_end - cur_offset);
                        if (ret) {
                                /*
                                 * We couldn't clear our area, so we could
                                 * presumably adjust up and corrupt the fs, so
                                 * we need to abort.
                                 */
                                btrfs_abort_transaction(trans, ret);
                                break;
                        }
                }

                if (extent_info &&
                    drop_args.drop_end > extent_info->file_offset) {
                        u64 replace_len = drop_args.drop_end -
                                          extent_info->file_offset;

                        ret = btrfs_insert_replace_extent(trans, inode, path,
                                        extent_info, replace_len,
                                        drop_args.bytes_found);
                        if (ret) {
                                btrfs_abort_transaction(trans, ret);
                                break;
                        }
                        extent_info->data_len -= replace_len;
                        extent_info->data_offset += replace_len;
                        extent_info->file_offset += replace_len;
                }

                /*
                 * We are releasing our handle on the transaction, balance the
                 * dirty pages of the btree inode and flush delayed items, and
                 * then get a new transaction handle, which may now point to a
                 * new transaction in case someone else may have committed the
                 * transaction we used to replace/drop file extent items. So
                 * bump the inode's iversion and update mtime and ctime except
                 * if we are called from a dedupe context. This is because a
                 * power failure/crash may happen after the transaction is
                 * committed and before we finish replacing/dropping all the
                 * file extent items we need.
                 */
                inode_inc_iversion(&inode->vfs_inode);

                if (!extent_info || extent_info->update_times) {
                        inode->vfs_inode.i_mtime = current_time(&inode->vfs_inode);
                        inode->vfs_inode.i_ctime = inode->vfs_inode.i_mtime;
                }

                ret = btrfs_update_inode(trans, root, inode);
                if (ret)
                        break;

                btrfs_end_transaction(trans);
                btrfs_btree_balance_dirty(fs_info);

                trans = btrfs_start_transaction(root, rsv_count);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        trans = NULL;
                        break;
                }

                ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv,
                                              rsv, min_size, false);
                if (WARN_ON(ret))
                        break;
                trans->block_rsv = rsv;

                cur_offset = drop_args.drop_end;
                len = end - cur_offset;
                if (!extent_info && len) {
                        ret = find_first_non_hole(inode, &cur_offset, &len);
                        if (unlikely(ret < 0))
                                break;
                        if (ret && !len) {
                                ret = 0;
                                break;
                        }
                }
        }

        /*
         * If we were cloning, force the next fsync to be a full one since we
         * we replaced (or just dropped in the case of cloning holes when
         * NO_HOLES is enabled) file extent items and did not setup new extent
         * maps for the replacement extents (or holes).
         */
        if (extent_info && !extent_info->is_new_extent)
                btrfs_set_inode_full_sync(inode);

        if (ret)
                goto out_trans;

        trans->block_rsv = &fs_info->trans_block_rsv;
        /*
         * If we are using the NO_HOLES feature we might have had already an
         * hole that overlaps a part of the region [lockstart, lockend] and
         * ends at (or beyond) lockend. Since we have no file extent items to
         * represent holes, drop_end can be less than lockend and so we must
         * make sure we have an extent map representing the existing hole (the
         * call to __btrfs_drop_extents() might have dropped the existing extent
         * map representing the existing hole), otherwise the fast fsync path
         * will not record the existence of the hole region
         * [existing_hole_start, lockend].
         */
        if (drop_args.drop_end <= end)
                drop_args.drop_end = end + 1;
        /*
         * Don't insert file hole extent item if it's for a range beyond eof
         * (because it's useless) or if it represents a 0 bytes range (when
         * cur_offset == drop_end).
         */
        if (!extent_info && cur_offset < ino_size &&
            cur_offset < drop_args.drop_end) {
                ret = fill_holes(trans, inode, path, cur_offset,
                                 drop_args.drop_end);
                if (ret) {
                        /* Same comment as above. */
                        btrfs_abort_transaction(trans, ret);
                        goto out_trans;
                }
        } else if (!extent_info && cur_offset < drop_args.drop_end) {
                /* See the comment in the loop above for the reasoning here. */
                ret = btrfs_inode_clear_file_extent_range(inode, cur_offset,
                                        drop_args.drop_end - cur_offset);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out_trans;
                }

        }
        if (extent_info) {
                ret = btrfs_insert_replace_extent(trans, inode, path,
                                extent_info, extent_info->data_len,
                                drop_args.bytes_found);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out_trans;
                }
        }

out_trans:
        if (!trans)
                goto out_free;

        trans->block_rsv = &fs_info->trans_block_rsv;
        if (ret)
                btrfs_end_transaction(trans);
        else
                *trans_out = trans;
out_free:
        btrfs_free_block_rsv(fs_info, rsv);
out:
        return ret;
}

static int btrfs_punch_hole(struct file *file, loff_t offset, loff_t len)
{
        struct inode *inode = file_inode(file);
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct extent_state *cached_state = NULL;
        struct btrfs_path *path;
        struct btrfs_trans_handle *trans = NULL;
        u64 lockstart;
        u64 lockend;
        u64 tail_start;
        u64 tail_len;
        u64 orig_start = offset;
        int ret = 0;
        bool same_block;
        u64 ino_size;
        bool truncated_block = false;
        bool updated_inode = false;

        btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);

        ret = btrfs_wait_ordered_range(inode, offset, len);
        if (ret)
                goto out_only_mutex;

        ino_size = round_up(inode->i_size, fs_info->sectorsize);
        ret = find_first_non_hole(BTRFS_I(inode), &offset, &len);
        if (ret < 0)
                goto out_only_mutex;
        if (ret && !len) {
                /* Already in a large hole */
                ret = 0;
                goto out_only_mutex;
        }

        ret = file_modified(file);
        if (ret)
                goto out_only_mutex;

        lockstart = round_up(offset, fs_info->sectorsize);
        lockend = round_down(offset + len, fs_info->sectorsize) - 1;
        same_block = (BTRFS_BYTES_TO_BLKS(fs_info, offset))
                == (BTRFS_BYTES_TO_BLKS(fs_info, offset + len - 1));
        /*
         * We needn't truncate any block which is beyond the end of the file
         * because we are sure there is no data there.
         */
        /*
         * Only do this if we are in the same block and we aren't doing the
         * entire block.
         */
        if (same_block && len < fs_info->sectorsize) {
                if (offset < ino_size) {
                        truncated_block = true;
                        ret = btrfs_truncate_block(BTRFS_I(inode), offset, len,
                                                   0);
                } else {
                        ret = 0;
                }
                goto out_only_mutex;
        }

        /* zero back part of the first block */
        if (offset < ino_size) {
                truncated_block = true;
                ret = btrfs_truncate_block(BTRFS_I(inode), offset, 0, 0);
                if (ret) {
                        btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
                        return ret;
                }
        }

        /* Check the aligned pages after the first unaligned page,
         * if offset != orig_start, which means the first unaligned page
         * including several following pages are already in holes,
         * the extra check can be skipped */
        if (offset == orig_start) {
                /* after truncate page, check hole again */
                len = offset + len - lockstart;
                offset = lockstart;
                ret = find_first_non_hole(BTRFS_I(inode), &offset, &len);
                if (ret < 0)
                        goto out_only_mutex;
                if (ret && !len) {
                        ret = 0;
                        goto out_only_mutex;
                }
                lockstart = offset;
        }

        /* Check the tail unaligned part is in a hole */
        tail_start = lockend + 1;
        tail_len = offset + len - tail_start;
        if (tail_len) {
                ret = find_first_non_hole(BTRFS_I(inode), &tail_start, &tail_len);
                if (unlikely(ret < 0))
                        goto out_only_mutex;
                if (!ret) {
                        /* zero the front end of the last page */
                        if (tail_start + tail_len < ino_size) {
                                truncated_block = true;
                                ret = btrfs_truncate_block(BTRFS_I(inode),
                                                        tail_start + tail_len,
                                                        0, 1);
                                if (ret)
                                        goto out_only_mutex;
                        }
                }
        }

        if (lockend < lockstart) {
                ret = 0;
                goto out_only_mutex;
        }

        btrfs_punch_hole_lock_range(inode, lockstart, lockend, &cached_state);

        path = btrfs_alloc_path();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        ret = btrfs_replace_file_extents(BTRFS_I(inode), path, lockstart,
                                         lockend, NULL, &trans);
        btrfs_free_path(path);
        if (ret)
                goto out;

        ASSERT(trans != NULL);
        inode_inc_iversion(inode);
        inode->i_mtime = current_time(inode);
        inode->i_ctime = inode->i_mtime;
        ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
        updated_inode = true;
        btrfs_end_transaction(trans);
        btrfs_btree_balance_dirty(fs_info);
out:
        unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                      &cached_state);
out_only_mutex:
        if (!updated_inode && truncated_block && !ret) {
                /*
                 * If we only end up zeroing part of a page, we still need to
                 * update the inode item, so that all the time fields are
                 * updated as well as the necessary btrfs inode in memory fields
                 * for detecting, at fsync time, if the inode isn't yet in the
                 * log tree or it's there but not up to date.
                 */
                struct timespec64 now = current_time(inode);

                inode_inc_iversion(inode);
                inode->i_mtime = now;
                inode->i_ctime = now;
                trans = btrfs_start_transaction(root, 1);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                } else {
                        int ret2;

                        ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
                        ret2 = btrfs_end_transaction(trans);
                        if (!ret)
                                ret = ret2;
                }
        }
        btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
        return ret;
}

/* Helper structure to record which range is already reserved */
struct falloc_range {
        struct list_head list;
        u64 start;
        u64 len;
};

/*
 * Helper function to add falloc range
 *
 * Caller should have locked the larger range of extent containing
 * [start, len)
 */
static int add_falloc_range(struct list_head *head, u64 start, u64 len)
{
        struct falloc_range *range = NULL;

        if (!list_empty(head)) {
                /*
                 * As fallocate iterates by bytenr order, we only need to check
                 * the last range.
                 */
                range = list_last_entry(head, struct falloc_range, list);
                if (range->start + range->len == start) {
                        range->len += len;
                        return 0;
                }
        }

        range = kmalloc(sizeof(*range), GFP_KERNEL);
        if (!range)
                return -ENOMEM;
        range->start = start;
        range->len = len;
        list_add_tail(&range->list, head);
        return 0;
}

static int btrfs_fallocate_update_isize(struct inode *inode,
                                        const u64 end,
                                        const int mode)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        int ret;
        int ret2;

        if (mode & FALLOC_FL_KEEP_SIZE || end <= i_size_read(inode))
                return 0;

        trans = btrfs_start_transaction(root, 1);
        if (IS_ERR(trans))
                return PTR_ERR(trans);

        inode->i_ctime = current_time(inode);
        i_size_write(inode, end);
        btrfs_inode_safe_disk_i_size_write(BTRFS_I(inode), 0);
        ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
        ret2 = btrfs_end_transaction(trans);

        return ret ? ret : ret2;
}

enum {
        RANGE_BOUNDARY_WRITTEN_EXTENT,
        RANGE_BOUNDARY_PREALLOC_EXTENT,
        RANGE_BOUNDARY_HOLE,
};

static int btrfs_zero_range_check_range_boundary(struct btrfs_inode *inode,
                                                 u64 offset)
{
        const u64 sectorsize = inode->root->fs_info->sectorsize;
        struct extent_map *em;
        int ret;

        offset = round_down(offset, sectorsize);
        em = btrfs_get_extent(inode, NULL, 0, offset, sectorsize);
        if (IS_ERR(em))
                return PTR_ERR(em);

        if (em->block_start == EXTENT_MAP_HOLE)
                ret = RANGE_BOUNDARY_HOLE;
        else if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
                ret = RANGE_BOUNDARY_PREALLOC_EXTENT;
        else
                ret = RANGE_BOUNDARY_WRITTEN_EXTENT;

        free_extent_map(em);
        return ret;
}

static int btrfs_zero_range(struct inode *inode,
                            loff_t offset,
                            loff_t len,
                            const int mode)
{
        struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
        struct extent_map *em;
        struct extent_changeset *data_reserved = NULL;
        int ret;
        u64 alloc_hint = 0;
        const u64 sectorsize = fs_info->sectorsize;
        u64 alloc_start = round_down(offset, sectorsize);
        u64 alloc_end = round_up(offset + len, sectorsize);
        u64 bytes_to_reserve = 0;
        bool space_reserved = false;

        em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, alloc_start,
                              alloc_end - alloc_start);
        if (IS_ERR(em)) {
                ret = PTR_ERR(em);
                goto out;
        }

        /*
         * Avoid hole punching and extent allocation for some cases. More cases
         * could be considered, but these are unlikely common and we keep things
         * as simple as possible for now. Also, intentionally, if the target
         * range contains one or more prealloc extents together with regular
         * extents and holes, we drop all the existing extents and allocate a
         * new prealloc extent, so that we get a larger contiguous disk extent.
         */
        if (em->start <= alloc_start &&
            test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) {
                const u64 em_end = em->start + em->len;

                if (em_end >= offset + len) {
                        /*
                         * The whole range is already a prealloc extent,
                         * do nothing except updating the inode's i_size if
                         * needed.
                         */
                        free_extent_map(em);
                        ret = btrfs_fallocate_update_isize(inode, offset + len,
                                                           mode);
                        goto out;
                }
                /*
                 * Part of the range is already a prealloc extent, so operate
                 * only on the remaining part of the range.
                 */
                alloc_start = em_end;
                ASSERT(IS_ALIGNED(alloc_start, sectorsize));
                len = offset + len - alloc_start;
                offset = alloc_start;
                alloc_hint = em->block_start + em->len;
        }
        free_extent_map(em);

        if (BTRFS_BYTES_TO_BLKS(fs_info, offset) ==
            BTRFS_BYTES_TO_BLKS(fs_info, offset + len - 1)) {
                em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, alloc_start,
                                      sectorsize);
                if (IS_ERR(em)) {
                        ret = PTR_ERR(em);
                        goto out;
                }

                if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) {
                        free_extent_map(em);
                        ret = btrfs_fallocate_update_isize(inode, offset + len,
                                                           mode);
                        goto out;
                }
                if (len < sectorsize && em->block_start != EXTENT_MAP_HOLE) {
                        free_extent_map(em);
                        ret = btrfs_truncate_block(BTRFS_I(inode), offset, len,
                                                   0);
                        if (!ret)
                                ret = btrfs_fallocate_update_isize(inode,
                                                                   offset + len,
                                                                   mode);
                        return ret;
                }
                free_extent_map(em);
                alloc_start = round_down(offset, sectorsize);
                alloc_end = alloc_start + sectorsize;
                goto reserve_space;
        }

        alloc_start = round_up(offset, sectorsize);
        alloc_end = round_down(offset + len, sectorsize);

        /*
         * For unaligned ranges, check the pages at the boundaries, they might
         * map to an extent, in which case we need to partially zero them, or
         * they might map to a hole, in which case we need our allocation range
         * to cover them.
         */
        if (!IS_ALIGNED(offset, sectorsize)) {
                ret = btrfs_zero_range_check_range_boundary(BTRFS_I(inode),
                                                            offset);
                if (ret < 0)
                        goto out;
                if (ret == RANGE_BOUNDARY_HOLE) {
                        alloc_start = round_down(offset, sectorsize);
                        ret = 0;
                } else if (ret == RANGE_BOUNDARY_WRITTEN_EXTENT) {
                        ret = btrfs_truncate_block(BTRFS_I(inode), offset, 0, 0);
                        if (ret)
                                goto out;
                } else {
                        ret = 0;
                }
        }

        if (!IS_ALIGNED(offset + len, sectorsize)) {
                ret = btrfs_zero_range_check_range_boundary(BTRFS_I(inode),
                                                            offset + len);
                if (ret < 0)
                        goto out;
                if (ret == RANGE_BOUNDARY_HOLE) {
                        alloc_end = round_up(offset + len, sectorsize);
                        ret = 0;
                } else if (ret == RANGE_BOUNDARY_WRITTEN_EXTENT) {
                        ret = btrfs_truncate_block(BTRFS_I(inode), offset + len,
                                                   0, 1);
                        if (ret)
                                goto out;
                } else {
                        ret = 0;
                }
        }

reserve_space:
        if (alloc_start < alloc_end) {
                struct extent_state *cached_state = NULL;
                const u64 lockstart = alloc_start;
                const u64 lockend = alloc_end - 1;

                bytes_to_reserve = alloc_end - alloc_start;
                ret = btrfs_alloc_data_chunk_ondemand(BTRFS_I(inode),
                                                      bytes_to_reserve);
                if (ret < 0)
                        goto out;
                space_reserved = true;
                btrfs_punch_hole_lock_range(inode, lockstart, lockend,
                                            &cached_state);
                ret = btrfs_qgroup_reserve_data(BTRFS_I(inode), &data_reserved,
                                                alloc_start, bytes_to_reserve);
                if (ret) {
                        unlock_extent(&BTRFS_I(inode)->io_tree, lockstart,
                                      lockend, &cached_state);
                        goto out;
                }
                ret = btrfs_prealloc_file_range(inode, mode, alloc_start,
                                                alloc_end - alloc_start,
                                                i_blocksize(inode),
                                                offset + len, &alloc_hint);
                unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                              &cached_state);
                /* btrfs_prealloc_file_range releases reserved space on error */
                if (ret) {
                        space_reserved = false;
                        goto out;
                }
        }
        ret = btrfs_fallocate_update_isize(inode, offset + len, mode);
 out:
        if (ret && space_reserved)
                btrfs_free_reserved_data_space(BTRFS_I(inode), data_reserved,
                                               alloc_start, bytes_to_reserve);
        extent_changeset_free(data_reserved);

        return ret;
}

static long btrfs_fallocate(struct file *file, int mode,
                            loff_t offset, loff_t len)
{
        struct inode *inode = file_inode(file);
        struct extent_state *cached_state = NULL;
        struct extent_changeset *data_reserved = NULL;
        struct falloc_range *range;
        struct falloc_range *tmp;
        LIST_HEAD(reserve_list);
        u64 cur_offset;
        u64 last_byte;
        u64 alloc_start;
        u64 alloc_end;
        u64 alloc_hint = 0;
        u64 locked_end;
        u64 actual_end = 0;
        u64 data_space_needed = 0;
        u64 data_space_reserved = 0;
        u64 qgroup_reserved = 0;
        struct extent_map *em;
        int blocksize = BTRFS_I(inode)->root->fs_info->sectorsize;
        int ret;

        /* Do not allow fallocate in ZONED mode */
        if (btrfs_is_zoned(btrfs_sb(inode->i_sb)))
                return -EOPNOTSUPP;

        alloc_start = round_down(offset, blocksize);
        alloc_end = round_up(offset + len, blocksize);
        cur_offset = alloc_start;

        /* Make sure we aren't being give some crap mode */
        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
                     FALLOC_FL_ZERO_RANGE))
                return -EOPNOTSUPP;

        if (mode & FALLOC_FL_PUNCH_HOLE)
                return btrfs_punch_hole(file, offset, len);

        btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);

        if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size) {
                ret = inode_newsize_ok(inode, offset + len);
                if (ret)
                        goto out;
        }

        ret = file_modified(file);
        if (ret)
                goto out;

        /*
         * TODO: Move these two operations after we have checked
         * accurate reserved space, or fallocate can still fail but
         * with page truncated or size expanded.
         *
         * But that's a minor problem and won't do much harm BTW.
         */
        if (alloc_start > inode->i_size) {
                ret = btrfs_cont_expand(BTRFS_I(inode), i_size_read(inode),
                                        alloc_start);
                if (ret)
                        goto out;
        } else if (offset + len > inode->i_size) {
                /*
                 * If we are fallocating from the end of the file onward we
                 * need to zero out the end of the block if i_size lands in the
                 * middle of a block.
                 */
                ret = btrfs_truncate_block(BTRFS_I(inode), inode->i_size, 0, 0);
                if (ret)
                        goto out;
        }

        /*
         * We have locked the inode at the VFS level (in exclusive mode) and we
         * have locked the i_mmap_lock lock (in exclusive mode). Now before
         * locking the file range, flush all dealloc in the range and wait for
         * all ordered extents in the range to complete. After this we can lock
         * the file range and, due to the previous locking we did, we know there
         * can't be more delalloc or ordered extents in the range.
         */
        ret = btrfs_wait_ordered_range(inode, alloc_start,
                                       alloc_end - alloc_start);
        if (ret)
                goto out;

        if (mode & FALLOC_FL_ZERO_RANGE) {
                ret = btrfs_zero_range(inode, offset, len, mode);
                btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
                return ret;
        }

        locked_end = alloc_end - 1;
        lock_extent(&BTRFS_I(inode)->io_tree, alloc_start, locked_end,
                    &cached_state);

        btrfs_assert_inode_range_clean(BTRFS_I(inode), alloc_start, locked_end);

        /* First, check if we exceed the qgroup limit */
        while (cur_offset < alloc_end) {
                em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, cur_offset,
                                      alloc_end - cur_offset);
                if (IS_ERR(em)) {
                        ret = PTR_ERR(em);
                        break;
                }
                last_byte = min(extent_map_end(em), alloc_end);
                actual_end = min_t(u64, extent_map_end(em), offset + len);
                last_byte = ALIGN(last_byte, blocksize);
                if (em->block_start == EXTENT_MAP_HOLE ||
                    (cur_offset >= inode->i_size &&
                     !test_bit(EXTENT_FLAG_PREALLOC, &em->flags))) {
                        const u64 range_len = last_byte - cur_offset;

                        ret = add_falloc_range(&reserve_list, cur_offset, range_len);
                        if (ret < 0) {
                                free_extent_map(em);
                                break;
                        }
                        ret = btrfs_qgroup_reserve_data(BTRFS_I(inode),
                                        &data_reserved, cur_offset, range_len);
                        if (ret < 0) {
                                free_extent_map(em);
                                break;
                        }
                        qgroup_reserved += range_len;
                        data_space_needed += range_len;
                }
                free_extent_map(em);
                cur_offset = last_byte;
        }

        if (!ret && data_space_needed > 0) {
                /*
                 * We are safe to reserve space here as we can't have delalloc
                 * in the range, see above.
                 */
                ret = btrfs_alloc_data_chunk_ondemand(BTRFS_I(inode),
                                                      data_space_needed);
                if (!ret)
                        data_space_reserved = data_space_needed;
        }

        /*
         * If ret is still 0, means we're OK to fallocate.
         * Or just cleanup the list and exit.
         */
        list_for_each_entry_safe(range, tmp, &reserve_list, list) {
                if (!ret) {
                        ret = btrfs_prealloc_file_range(inode, mode,
                                        range->start,
                                        range->len, i_blocksize(inode),
                                        offset + len, &alloc_hint);
                        /*
                         * btrfs_prealloc_file_range() releases space even
                         * if it returns an error.
                         */
                        data_space_reserved -= range->len;
                        qgroup_reserved -= range->len;
                } else if (data_space_reserved > 0) {
                        btrfs_free_reserved_data_space(BTRFS_I(inode),
                                               data_reserved, range->start,
                                               range->len);
                        data_space_reserved -= range->len;
                        qgroup_reserved -= range->len;
                } else if (qgroup_reserved > 0) {
                        btrfs_qgroup_free_data(BTRFS_I(inode), data_reserved,
                                               range->start, range->len);
                        qgroup_reserved -= range->len;
                }
                list_del(&range->list);
                kfree(range);
        }
        if (ret < 0)
                goto out_unlock;

        /*
         * We didn't need to allocate any more space, but we still extended the
         * size of the file so we need to update i_size and the inode item.
         */
        ret = btrfs_fallocate_update_isize(inode, actual_end, mode);
out_unlock:
        unlock_extent(&BTRFS_I(inode)->io_tree, alloc_start, locked_end,
                      &cached_state);
out:
        btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
        extent_changeset_free(data_reserved);
        return ret;
}

/*
 * Helper for btrfs_find_delalloc_in_range(). Find a subrange in a given range
 * that has unflushed and/or flushing delalloc. There might be other adjacent
 * subranges after the one it found, so btrfs_find_delalloc_in_range() keeps
 * looping while it gets adjacent subranges, and merging them together.
 */
static bool find_delalloc_subrange(struct btrfs_inode *inode, u64 start, u64 end,
                                   struct extent_state **cached_state,
                                   bool *search_io_tree,
                                   u64 *delalloc_start_ret, u64 *delalloc_end_ret)
{
        u64 len = end + 1 - start;
        u64 delalloc_len = 0;
        struct btrfs_ordered_extent *oe;
        u64 oe_start;
        u64 oe_end;

        /*
         * Search the io tree first for EXTENT_DELALLOC. If we find any, it
         * means we have delalloc (dirty pages) for which writeback has not
         * started yet.
         */
        if (*search_io_tree) {
                spin_lock(&inode->lock);
                if (inode->delalloc_bytes > 0) {
                        spin_unlock(&inode->lock);
                        *delalloc_start_ret = start;
                        delalloc_len = count_range_bits(&inode->io_tree,
                                                        delalloc_start_ret, end,
                                                        len, EXTENT_DELALLOC, 1,
                                                        cached_state);
                } else {
                        spin_unlock(&inode->lock);
                }
        }

        if (delalloc_len > 0) {
                /*
                 * If delalloc was found then *delalloc_start_ret has a sector size
                 * aligned value (rounded down).
                 */
                *delalloc_end_ret = *delalloc_start_ret + delalloc_len - 1;

                if (*delalloc_start_ret == start) {
                        /* Delalloc for the whole range, nothing more to do. */
                        if (*delalloc_end_ret == end)
                                return true;
                        /* Else trim our search range for ordered extents. */
                        start = *delalloc_end_ret + 1;
                        len = end + 1 - start;
                }
        } else {
                /* No delalloc, future calls don't need to search again. */
                *search_io_tree = false;
        }

        /*
         * Now also check if there's any ordered extent in the range.
         * We do this because:
         *
         * 1) When delalloc is flushed, the file range is locked, we clear the
         *    EXTENT_DELALLOC bit from the io tree and create an extent map and
         *    an ordered extent for the write. So we might just have been called
         *    after delalloc is flushed and before the ordered extent completes
         *    and inserts the new file extent item in the subvolume's btree;
         *
         * 2) We may have an ordered extent created by flushing delalloc for a
         *    subrange that starts before the subrange we found marked with
         *    EXTENT_DELALLOC in the io tree.
         *
         * We could also use the extent map tree to find such delalloc that is
         * being flushed, but using the ordered extents tree is more efficient
         * because it's usually much smaller as ordered extents are removed from
         * the tree once they complete. With the extent maps, we mau have them
         * in the extent map tree for a very long time, and they were either
         * created by previous writes or loaded by read operations.
         */
        oe = btrfs_lookup_first_ordered_range(inode, start, len);
        if (!oe)
                return (delalloc_len > 0);

        /* The ordered extent may span beyond our search range. */
        oe_start = max(oe->file_offset, start);
        oe_end = min(oe->file_offset + oe->num_bytes - 1, end);

        btrfs_put_ordered_extent(oe);

        /* Don't have unflushed delalloc, return the ordered extent range. */
        if (delalloc_len == 0) {
                *delalloc_start_ret = oe_start;
                *delalloc_end_ret = oe_end;
                return true;
        }

        /*
         * We have both unflushed delalloc (io_tree) and an ordered extent.
         * If the ranges are adjacent returned a combined range, otherwise
         * return the leftmost range.
         */
        if (oe_start < *delalloc_start_ret) {
                if (oe_end < *delalloc_start_ret)
                        *delalloc_end_ret = oe_end;
                *delalloc_start_ret = oe_start;
        } else if (*delalloc_end_ret + 1 == oe_start) {
                *delalloc_end_ret = oe_end;
        }

        return true;
}

/*
 * Check if there's delalloc in a given range.
 *
 * @inode:               The inode.
 * @start:               The start offset of the range. It does not need to be
 *                       sector size aligned.
 * @end:                 The end offset (inclusive value) of the search range.
 *                       It does not need to be sector size aligned.
 * @cached_state:        Extent state record used for speeding up delalloc
 *                       searches in the inode's io_tree. Can be NULL.
 * @delalloc_start_ret:  Output argument, set to the start offset of the
 *                       subrange found with delalloc (may not be sector size
 *                       aligned).
 * @delalloc_end_ret:    Output argument, set to he end offset (inclusive value)
 *                       of the subrange found with delalloc.
 *
 * Returns true if a subrange with delalloc is found within the given range, and
 * if so it sets @delalloc_start_ret and @delalloc_end_ret with the start and
 * end offsets of the subrange.
 */
bool btrfs_find_delalloc_in_range(struct btrfs_inode *inode, u64 start, u64 end,
                                  struct extent_state **cached_state,
                                  u64 *delalloc_start_ret, u64 *delalloc_end_ret)
{
        u64 cur_offset = round_down(start, inode->root->fs_info->sectorsize);
        u64 prev_delalloc_end = 0;
        bool search_io_tree = true;
        bool ret = false;

        while (cur_offset <= end) {
                u64 delalloc_start;
                u64 delalloc_end;
                bool delalloc;

                delalloc = find_delalloc_subrange(inode, cur_offset, end,
                                                  cached_state, &search_io_tree,
                                                  &delalloc_start,
                                                  &delalloc_end);
                if (!delalloc)
                        break;

                if (prev_delalloc_end == 0) {
                        /* First subrange found. */
                        *delalloc_start_ret = max(delalloc_start, start);
                        *delalloc_end_ret = delalloc_end;
                        ret = true;
                } else if (delalloc_start == prev_delalloc_end + 1) {
                        /* Subrange adjacent to the previous one, merge them. */
                        *delalloc_end_ret = delalloc_end;
                } else {
                        /* Subrange not adjacent to the previous one, exit. */
                        break;
                }

                prev_delalloc_end = delalloc_end;
                cur_offset = delalloc_end + 1;
                cond_resched();
        }

        return ret;
}

/*
 * Check if there's a hole or delalloc range in a range representing a hole (or
 * prealloc extent) found in the inode's subvolume btree.
 *
 * @inode:      The inode.
 * @whence:     Seek mode (SEEK_DATA or SEEK_HOLE).
 * @start:      Start offset of the hole region. It does not need to be sector
 *              size aligned.
 * @end:        End offset (inclusive value) of the hole region. It does not
 *              need to be sector size aligned.
 * @start_ret:  Return parameter, used to set the start of the subrange in the
 *              hole that matches the search criteria (seek mode), if such
 *              subrange is found (return value of the function is true).
 *              The value returned here may not be sector size aligned.
 *
 * Returns true if a subrange matching the given seek mode is found, and if one
 * is found, it updates @start_ret with the start of the subrange.
 */
static bool find_desired_extent_in_hole(struct btrfs_inode *inode, int whence,
                                        struct extent_state **cached_state,
                                        u64 start, u64 end, u64 *start_ret)
{
        u64 delalloc_start;
        u64 delalloc_end;
        bool delalloc;

        delalloc = btrfs_find_delalloc_in_range(inode, start, end, cached_state,
                                                &delalloc_start, &delalloc_end);
        if (delalloc && whence == SEEK_DATA) {
                *start_ret = delalloc_start;
                return true;
        }

        if (delalloc && whence == SEEK_HOLE) {
                /*
                 * We found delalloc but it starts after out start offset. So we
                 * have a hole between our start offset and the delalloc start.
                 */
                if (start < delalloc_start) {
                        *start_ret = start;
                        return true;
                }
                /*
                 * Delalloc range starts at our start offset.
                 * If the delalloc range's length is smaller than our range,
                 * then it means we have a hole that starts where the delalloc
                 * subrange ends.
                 */
                if (delalloc_end < end) {
                        *start_ret = delalloc_end + 1;
                        return true;
                }

                /* There's delalloc for the whole range. */
                return false;
        }

        if (!delalloc && whence == SEEK_HOLE) {
                *start_ret = start;
                return true;
        }

        /*
         * No delalloc in the range and we are seeking for data. The caller has
         * to iterate to the next extent item in the subvolume btree.
         */
        return false;
}

static loff_t find_desired_extent(struct file *file, loff_t offset, int whence)
{
        struct btrfs_inode *inode = BTRFS_I(file->f_mapping->host);
        struct btrfs_file_private *private = file->private_data;
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct extent_state *cached_state = NULL;
        struct extent_state **delalloc_cached_state;
        const loff_t i_size = i_size_read(&inode->vfs_inode);
        const u64 ino = btrfs_ino(inode);
        struct btrfs_root *root = inode->root;
        struct btrfs_path *path;
        struct btrfs_key key;
        u64 last_extent_end;
        u64 lockstart;
        u64 lockend;
        u64 start;
        int ret;
        bool found = false;

        if (i_size == 0 || offset >= i_size)
                return -ENXIO;

        /*
         * Quick path. If the inode has no prealloc extents and its number of
         * bytes used matches its i_size, then it can not have holes.
         */
        if (whence == SEEK_HOLE &&
            !(inode->flags & BTRFS_INODE_PREALLOC) &&
            inode_get_bytes(&inode->vfs_inode) == i_size)
                return i_size;

        if (!private) {
                private = kzalloc(sizeof(*private), GFP_KERNEL);
                /*
                 * No worries if memory allocation failed.
                 * The private structure is used only for speeding up multiple
                 * lseek SEEK_HOLE/DATA calls to a file when there's delalloc,
                 * so everything will still be correct.
                 */
                file->private_data = private;
        }

        if (private)
                delalloc_cached_state = &private->llseek_cached_state;
        else
                delalloc_cached_state = NULL;

        /*
         * offset can be negative, in this case we start finding DATA/HOLE from
         * the very start of the file.
         */
        start = max_t(loff_t, 0, offset);

        lockstart = round_down(start, fs_info->sectorsize);
        lockend = round_up(i_size, fs_info->sectorsize);
        if (lockend <= lockstart)
                lockend = lockstart + fs_info->sectorsize;
        lockend--;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        path->reada = READA_FORWARD;

        key.objectid = ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = start;

        last_extent_end = lockstart;

        lock_extent(&inode->io_tree, lockstart, lockend, &cached_state);

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0) {
                goto out;
        } else if (ret > 0 && path->slots[0] > 0) {
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0] - 1);
                if (key.objectid == ino && key.type == BTRFS_EXTENT_DATA_KEY)
                        path->slots[0]--;
        }

        while (start < i_size) {
                struct extent_buffer *leaf = path->nodes[0];
                struct btrfs_file_extent_item *extent;
                u64 extent_end;
                u8 type;

                if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                goto out;
                        else if (ret > 0)
                                break;

                        leaf = path->nodes[0];
                }

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY)
                        break;

                extent_end = btrfs_file_extent_end(path);

                /*
                 * In the first iteration we may have a slot that points to an
                 * extent that ends before our start offset, so skip it.
                 */
                if (extent_end <= start) {
                        path->slots[0]++;
                        continue;
                }

                /* We have an implicit hole, NO_HOLES feature is likely set. */
                if (last_extent_end < key.offset) {
                        u64 search_start = last_extent_end;
                        u64 found_start;

                        /*
                         * First iteration, @start matches @offset and it's
                         * within the hole.
                         */
                        if (start == offset)
                                search_start = offset;

                        found = find_desired_extent_in_hole(inode, whence,
                                                            delalloc_cached_state,
                                                            search_start,
                                                            key.offset - 1,
                                                            &found_start);
                        if (found) {
                                start = found_start;
                                break;
                        }
                        /*
                         * Didn't find data or a hole (due to delalloc) in the
                         * implicit hole range, so need to analyze the extent.
                         */
                }

                extent = btrfs_item_ptr(leaf, path->slots[0],
                                        struct btrfs_file_extent_item);
                type = btrfs_file_extent_type(leaf, extent);

                /*
                 * Can't access the extent's disk_bytenr field if this is an
                 * inline extent, since at that offset, it's where the extent
                 * data starts.
                 */
                if (type == BTRFS_FILE_EXTENT_PREALLOC ||
                    (type == BTRFS_FILE_EXTENT_REG &&
                     btrfs_file_extent_disk_bytenr(leaf, extent) == 0)) {
                        /*
                         * Explicit hole or prealloc extent, search for delalloc.
                         * A prealloc extent is treated like a hole.
                         */
                        u64 search_start = key.offset;
                        u64 found_start;

                        /*
                         * First iteration, @start matches @offset and it's
                         * within the hole.
                         */
                        if (start == offset)
                                search_start = offset;

                        found = find_desired_extent_in_hole(inode, whence,
                                                            delalloc_cached_state,
                                                            search_start,
                                                            extent_end - 1,
                                                            &found_start);
                        if (found) {
                                start = found_start;
                                break;
                        }
                        /*
                         * Didn't find data or a hole (due to delalloc) in the
                         * implicit hole range, so need to analyze the next
                         * extent item.
                         */
                } else {
                        /*
                         * Found a regular or inline extent.
                         * If we are seeking for data, adjust the start offset
                         * and stop, we're done.
                         */
                        if (whence == SEEK_DATA) {
                                start = max_t(u64, key.offset, offset);
                                found = true;
                                break;
                        }
                        /*
                         * Else, we are seeking for a hole, check the next file
                         * extent item.
                         */
                }

                start = extent_end;
                last_extent_end = extent_end;
                path->slots[0]++;
                if (fatal_signal_pending(current)) {
                        ret = -EINTR;
                        goto out;
                }
                cond_resched();
        }

        /* We have an implicit hole from the last extent found up to i_size. */
        if (!found && start < i_size) {
                found = find_desired_extent_in_hole(inode, whence,
                                                    delalloc_cached_state, start,
                                                    i_size - 1, &start);
                if (!found)
                        start = i_size;
        }

out:
        unlock_extent(&inode->io_tree, lockstart, lockend, &cached_state);
        btrfs_free_path(path);

        if (ret < 0)
                return ret;

        if (whence == SEEK_DATA && start >= i_size)
                return -ENXIO;

        return min_t(loff_t, start, i_size);
}

static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int whence)
{
        struct inode *inode = file->f_mapping->host;

        switch (whence) {
        default:
                return generic_file_llseek(file, offset, whence);
        case SEEK_DATA:
        case SEEK_HOLE:
                btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_SHARED);
                offset = find_desired_extent(file, offset, whence);
                btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_SHARED);
                break;
        }

        if (offset < 0)
                return offset;

        return vfs_setpos(file, offset, inode->i_sb->s_maxbytes);
}

static int btrfs_file_open(struct inode *inode, struct file *filp)
{
        int ret;

        filp->f_mode |= FMODE_NOWAIT | FMODE_BUF_RASYNC | FMODE_BUF_WASYNC |
                        FMODE_CAN_ODIRECT;

        ret = fsverity_file_open(inode, filp);
        if (ret)
                return ret;
        return generic_file_open(inode, filp);
}

static int check_direct_read(struct btrfs_fs_info *fs_info,
                             const struct iov_iter *iter, loff_t offset)
{
        int ret;
        int i, seg;

        ret = check_direct_IO(fs_info, iter, offset);
        if (ret < 0)
                return ret;

        if (!iter_is_iovec(iter))
                return 0;

        for (seg = 0; seg < iter->nr_segs; seg++) {
                for (i = seg + 1; i < iter->nr_segs; i++) {
                        const struct iovec *iov1 = iter_iov(iter) + seg;
                        const struct iovec *iov2 = iter_iov(iter) + i;

                        if (iov1->iov_base == iov2->iov_base)
                                return -EINVAL;
                }
        }
        return 0;
}

static ssize_t btrfs_direct_read(struct kiocb *iocb, struct iov_iter *to)
{
        struct inode *inode = file_inode(iocb->ki_filp);
        size_t prev_left = 0;
        ssize_t read = 0;
        ssize_t ret;

        if (fsverity_active(inode))
                return 0;

        if (check_direct_read(btrfs_sb(inode->i_sb), to, iocb->ki_pos))
                return 0;

        btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_SHARED);
again:
        /*
         * This is similar to what we do for direct IO writes, see the comment
         * at btrfs_direct_write(), but we also disable page faults in addition
         * to disabling them only at the iov_iter level. This is because when
         * reading from a hole or prealloc extent, iomap calls iov_iter_zero(),
         * which can still trigger page fault ins despite having set ->nofault
         * to true of our 'to' iov_iter.
         *
         * The difference to direct IO writes is that we deadlock when trying
         * to lock the extent range in the inode's tree during he page reads
         * triggered by the fault in (while for writes it is due to waiting for
         * our own ordered extent). This is because for direct IO reads,
         * btrfs_dio_iomap_begin() returns with the extent range locked, which
         * is only unlocked in the endio callback (end_bio_extent_readpage()).
         */
        pagefault_disable();
        to->nofault = true;
        ret = btrfs_dio_read(iocb, to, read);
        to->nofault = false;
        pagefault_enable();

        /* No increment (+=) because iomap returns a cumulative value. */
        if (ret > 0)
                read = ret;

        if (iov_iter_count(to) > 0 && (ret == -EFAULT || ret > 0)) {
                const size_t left = iov_iter_count(to);

                if (left == prev_left) {
                        /*
                         * We didn't make any progress since the last attempt,
                         * fallback to a buffered read for the remainder of the
                         * range. This is just to avoid any possibility of looping
                         * for too long.
                         */
                        ret = read;
                } else {
                        /*
                         * We made some progress since the last retry or this is
                         * the first time we are retrying. Fault in as many pages
                         * as possible and retry.
                         */
                        fault_in_iov_iter_writeable(to, left);
                        prev_left = left;
                        goto again;
                }
        }
        btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_SHARED);
        return ret < 0 ? ret : read;
}

static ssize_t btrfs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        ssize_t ret = 0;

        if (iocb->ki_flags & IOCB_DIRECT) {
                ret = btrfs_direct_read(iocb, to);
                if (ret < 0 || !iov_iter_count(to) ||
                    iocb->ki_pos >= i_size_read(file_inode(iocb->ki_filp)))
                        return ret;
        }

        return filemap_read(iocb, to, ret);
}

const struct file_operations btrfs_file_operations = {
        .llseek         = btrfs_file_llseek,
        .read_iter      = btrfs_file_read_iter,
        .splice_read    = filemap_splice_read,
        .write_iter     = btrfs_file_write_iter,
        .splice_write   = iter_file_splice_write,
        .mmap           = btrfs_file_mmap,
        .open           = btrfs_file_open,
        .release        = btrfs_release_file,
        .get_unmapped_area = thp_get_unmapped_area,
        .fsync          = btrfs_sync_file,
        .fallocate      = btrfs_fallocate,
        .unlocked_ioctl = btrfs_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl   = btrfs_compat_ioctl,
#endif
        .remap_file_range = btrfs_remap_file_range,
};

int btrfs_fdatawrite_range(struct inode *inode, loff_t start, loff_t end)
{
        int ret;

        /*
         * So with compression we will find and lock a dirty page and clear the
         * first one as dirty, setup an async extent, and immediately return
         * with the entire range locked but with nobody actually marked with
         * writeback.  So we can't just filemap_write_and_wait_range() and
         * expect it to work since it will just kick off a thread to do the
         * actual work.  So we need to call filemap_fdatawrite_range _again_
         * since it will wait on the page lock, which won't be unlocked until
         * after the pages have been marked as writeback and so we're good to go
         * from there.  We have to do this otherwise we'll miss the ordered
         * extents and that results in badness.  Please Josef, do not think you
         * know better and pull this out at some point in the future, it is
         * right and you are wrong.
         */
        ret = filemap_fdatawrite_range(inode->i_mapping, start, end);
        if (!ret && test_bit(BTRFS_INODE_HAS_ASYNC_EXTENT,
                             &BTRFS_I(inode)->runtime_flags))
                ret = filemap_fdatawrite_range(inode->i_mapping, start, end);

        return ret;
}