btrfs-progs: convert: Fix a bug in rollback check which overwrite return value

[platform/upstream/btrfs-progs.git] / convert / main.c

/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

/*
 * Btrfs convert design:
 *
 * The overall design of btrfs convert is like the following:
 *
 * |<------------------Old fs----------------------------->|
 * |<- used ->| |<- used ->|                    |<- used ->|
 *                           ||
 *                           \/
 * |<---------------Btrfs fs------------------------------>|
 * |<-   Old data chunk  ->|< new chunk (D/M/S)>|<- ODC  ->|
 * |<-Old-FE->| |<-Old-FE->|<- Btrfs extents  ->|<-Old-FE->|
 *
 * ODC    = Old data chunk, btrfs chunks containing old fs data
 *          Mapped 1:1 (logical address == device offset)
 * Old-FE = file extents pointing to old fs.
 *
 * So old fs used space is (mostly) kept as is, while btrfs will insert
 * its chunk (Data/Meta/Sys) into large enough free space.
 * In this way, we can create different profiles for metadata/data for
 * converted fs.
 *
 * We must reserve and relocate 3 ranges for btrfs:
 * * [0, 1M)                    - area never used for any data except the first
 *                                superblock
 * * [btrfs_sb_offset(1), +64K) - 1st superblock backup copy
 * * [btrfs_sb_offset(2), +64K) - 2nd, dtto
 *
 * Most work is spent handling corner cases around these reserved ranges.
 *
 * Detailed workflow is:
 * 1)   Scan old fs used space and calculate data chunk layout
 * 1.1) Scan old fs
 *      We can a map used space of old fs
 *
 * 1.2) Calculate data chunk layout - this is the hard part
 *      New data chunks must meet 3 conditions using result fomr 1.1
 *      a. Large enough to be a chunk
 *      b. Doesn't intersect reserved ranges
 *      c. Covers all the remaining old fs used space
 *
 *      NOTE: This can be simplified if we don't need to handle backup supers
 *
 * 1.3) Calculate usable space for new btrfs chunks
 *      Btrfs chunk usable space must meet 3 conditions using result from 1.2
 *      a. Large enough to be a chunk
 *      b. Doesn't intersect reserved ranges
 *      c. Doesn't cover any data chunks in 1.1
 *
 * 2)   Create basic btrfs filesystem structure
 *      Initial metadata and sys chunks are inserted in the first availabe
 *      space found in step 1.3
 *      Then insert all data chunks into the basic btrfs
 *
 * 3)   Create convert image
 *      We need to relocate reserved ranges here.
 *      After this step, the convert image is done, and we can use the image
 *      as reflink source to create old files
 *
 * 4)   Iterate old fs to create files
 *      We just reflink file extents from old fs to newly created files on
 *      btrfs.
 */

#include "kerncompat.h"

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <getopt.h>
#include <pthread.h>
#include <stdbool.h>

#include "ctree.h"
#include "disk-io.h"
#include "volumes.h"
#include "transaction.h"
#include "utils.h"
#include "task-utils.h"
#include "help.h"
#include "mkfs/common.h"
#include "convert/common.h"
#include "convert/source-fs.h"
#include "fsfeatures.h"

extern const struct btrfs_convert_operations ext2_convert_ops;
extern const struct btrfs_convert_operations reiserfs_convert_ops;

static const struct btrfs_convert_operations *convert_operations[] = {
#if BTRFSCONVERT_EXT2
        &ext2_convert_ops,
#endif
#if BTRFSCONVERT_REISERFS
        &reiserfs_convert_ops,
#endif
};

static void *print_copied_inodes(void *p)
{
        struct task_ctx *priv = p;
        const char work_indicator[] = { '.', 'o', 'O', 'o' };
        u64 count = 0;

        task_period_start(priv->info, 1000 /* 1s */);
        while (1) {
                count++;
                pthread_mutex_lock(&priv->mutex);
                printf("copy inodes [%c] [%10llu/%10llu]\r",
                       work_indicator[count % 4],
                       (unsigned long long)priv->cur_copy_inodes,
                       (unsigned long long)priv->max_copy_inodes);
                pthread_mutex_unlock(&priv->mutex);
                fflush(stdout);
                task_period_wait(priv->info);
        }

        return NULL;
}

static int after_copied_inodes(void *p)
{
        printf("\n");
        fflush(stdout);

        return 0;
}

static inline int copy_inodes(struct btrfs_convert_context *cctx,
                              struct btrfs_root *root, u32 convert_flags,
                              struct task_ctx *p)
{
        return cctx->convert_ops->copy_inodes(cctx, root, convert_flags, p);
}

static inline void convert_close_fs(struct btrfs_convert_context *cctx)
{
        cctx->convert_ops->close_fs(cctx);
}

static inline int convert_check_state(struct btrfs_convert_context *cctx)
{
        return cctx->convert_ops->check_state(cctx);
}

static int csum_disk_extent(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root,
                            u64 disk_bytenr, u64 num_bytes)
{
        u32 blocksize = root->fs_info->sectorsize;
        u64 offset;
        char *buffer;
        int ret = 0;

        buffer = malloc(blocksize);
        if (!buffer)
                return -ENOMEM;
        for (offset = 0; offset < num_bytes; offset += blocksize) {
                ret = read_disk_extent(root, disk_bytenr + offset,
                                        blocksize, buffer);
                if (ret)
                        break;
                ret = btrfs_csum_file_block(trans,
                                            root->fs_info->csum_root,
                                            disk_bytenr + num_bytes,
                                            disk_bytenr + offset,
                                            buffer, blocksize);
                if (ret)
                        break;
        }
        free(buffer);
        return ret;
}

static int create_image_file_range(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *root,
                                      struct cache_tree *used,
                                      struct btrfs_inode_item *inode,
                                      u64 ino, u64 bytenr, u64 *ret_len,
                                      u32 convert_flags)
{
        struct cache_extent *cache;
        struct btrfs_block_group_cache *bg_cache;
        u64 len = *ret_len;
        u64 disk_bytenr;
        int i;
        int ret;
        u32 datacsum = convert_flags & CONVERT_FLAG_DATACSUM;

        if (bytenr != round_down(bytenr, root->fs_info->sectorsize)) {
                error("bytenr not sectorsize aligned: %llu",
                                (unsigned long long)bytenr);
                return -EINVAL;
        }
        if (len != round_down(len, root->fs_info->sectorsize)) {
                error("length not sectorsize aligned: %llu",
                                (unsigned long long)len);
                return -EINVAL;
        }
        len = min_t(u64, len, BTRFS_MAX_EXTENT_SIZE);

        /*
         * Skip reserved ranges first
         *
         * Or we will insert a hole into current image file, and later
         * migrate block will fail as there is already a file extent.
         */
        for (i = 0; i < ARRAY_SIZE(btrfs_reserved_ranges); i++) {
                const struct simple_range *reserved = &btrfs_reserved_ranges[i];

                /*
                 * |-- reserved --|
                 *         |--range---|
                 * or
                 * |---- reserved ----|
                 *    |-- range --|
                 * Skip to reserved range end
                 */
                if (bytenr >= reserved->start && bytenr < range_end(reserved)) {
                        *ret_len = range_end(reserved) - bytenr;
                        return 0;
                }

                /*
                 *      |---reserved---|
                 * |----range-------|
                 * Leading part may still create a file extent
                 */
                if (bytenr < reserved->start &&
                    bytenr + len >= range_end(reserved)) {
                        len = min_t(u64, len, reserved->start - bytenr);
                        break;
                }
        }

        /* Check if we are going to insert regular file extent, or hole */
        cache = search_cache_extent(used, bytenr);
        if (cache) {
                if (cache->start <= bytenr) {
                        /*
                         * |///////Used///////|
                         *      |<--insert--->|
                         *      bytenr
                         * Insert one real file extent
                         */
                        len = min_t(u64, len, cache->start + cache->size -
                                    bytenr);
                        disk_bytenr = bytenr;
                } else {
                        /*
                         *              |//Used//|
                         *  |<-insert-->|
                         *  bytenr
                         *  Insert one hole
                         */
                        len = min(len, cache->start - bytenr);
                        disk_bytenr = 0;
                        datacsum = 0;
                }
        } else {
                /*
                 * |//Used//|           |EOF
                 *          |<-insert-->|
                 *          bytenr
                 * Insert one hole
                 */
                disk_bytenr = 0;
                datacsum = 0;
        }

        if (disk_bytenr) {
                /* Check if the range is in a data block group */
                bg_cache = btrfs_lookup_block_group(root->fs_info, bytenr);
                if (!bg_cache)
                        return -ENOENT;
                if (!(bg_cache->flags & BTRFS_BLOCK_GROUP_DATA))
                        return -EINVAL;

                /* The extent should never cross block group boundary */
                len = min_t(u64, len, bg_cache->key.objectid +
                            bg_cache->key.offset - bytenr);
        }

        if (len != round_down(len, root->fs_info->sectorsize)) {
                error("remaining length not sectorsize aligned: %llu",
                                (unsigned long long)len);
                return -EINVAL;
        }
        ret = btrfs_record_file_extent(trans, root, ino, inode, bytenr,
                                       disk_bytenr, len);
        if (ret < 0)
                return ret;

        if (datacsum)
                ret = csum_disk_extent(trans, root, bytenr, len);
        *ret_len = len;
        return ret;
}

/*
 * Relocate old fs data in one reserved ranges
 *
 * Since all old fs data in reserved range is not covered by any chunk nor
 * data extent, we don't need to handle any reference but add new
 * extent/reference, which makes codes more clear
 */
static int migrate_one_reserved_range(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *root,
                                      struct cache_tree *used,
                                      struct btrfs_inode_item *inode, int fd,
                                      u64 ino, const struct simple_range *range,
                                      u32 convert_flags)
{
        u64 cur_off = range->start;
        u64 cur_len = range->len;
        u64 hole_start = range->start;
        u64 hole_len;
        struct cache_extent *cache;
        struct btrfs_key key;
        struct extent_buffer *eb;
        int ret = 0;

        /*
         * It's possible that there are holes in reserved range:
         * |<---------------- Reserved range ---------------------->|
         *      |<- Old fs data ->|   |<- Old fs data ->|
         * So here we need to iterate through old fs used space and only
         * migrate ranges that covered by old fs data.
         */
        while (cur_off < range_end(range)) {
                cache = search_cache_extent(used, cur_off);
                if (!cache)
                        break;
                cur_off = max(cache->start, cur_off);
                if (cur_off >= range_end(range))
                        break;
                cur_len = min(cache->start + cache->size, range_end(range)) -
                          cur_off;
                BUG_ON(cur_len < root->fs_info->sectorsize);

                /* reserve extent for the data */
                ret = btrfs_reserve_extent(trans, root, cur_len, 0, 0, (u64)-1,
                                           &key, 1);
                if (ret < 0)
                        break;

                eb = malloc(sizeof(*eb) + cur_len);
                if (!eb) {
                        ret = -ENOMEM;
                        break;
                }

                ret = pread(fd, eb->data, cur_len, cur_off);
                if (ret < cur_len) {
                        ret = (ret < 0 ? ret : -EIO);
                        free(eb);
                        break;
                }
                eb->start = key.objectid;
                eb->len = key.offset;

                /* Write the data */
                ret = write_and_map_eb(root->fs_info, eb);
                free(eb);
                if (ret < 0)
                        break;

                /* Now handle extent item and file extent things */
                ret = btrfs_record_file_extent(trans, root, ino, inode, cur_off,
                                               key.objectid, key.offset);
                if (ret < 0)
                        break;
                /* Finally, insert csum items */
                if (convert_flags & CONVERT_FLAG_DATACSUM)
                        ret = csum_disk_extent(trans, root, key.objectid,
                                               key.offset);

                /* Don't forget to insert hole */
                hole_len = cur_off - hole_start;
                if (hole_len) {
                        ret = btrfs_record_file_extent(trans, root, ino, inode,
                                        hole_start, 0, hole_len);
                        if (ret < 0)
                                break;
                }

                cur_off += key.offset;
                hole_start = cur_off;
                cur_len = range_end(range) - cur_off;
        }
        /*
         * Last hole
         * |<---- reserved -------->|
         * |<- Old fs data ->|      |
         *                   | Hole |
         */
        if (range_end(range) - hole_start > 0)
                ret = btrfs_record_file_extent(trans, root, ino, inode,
                                hole_start, 0, range_end(range) - hole_start);
        return ret;
}

/*
 * Relocate the used source fs data in reserved ranges
 */
static int migrate_reserved_ranges(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root,
                                   struct cache_tree *used,
                                   struct btrfs_inode_item *inode, int fd,
                                   u64 ino, u64 total_bytes, u32 convert_flags)
{
        int i;
        int ret = 0;

        for (i = 0; i < ARRAY_SIZE(btrfs_reserved_ranges); i++) {
                const struct simple_range *range = &btrfs_reserved_ranges[i];

                if (range->start > total_bytes)
                        return ret;
                ret = migrate_one_reserved_range(trans, root, used, inode, fd,
                                                 ino, range, convert_flags);
                if (ret < 0)
                        return ret;
        }

        return ret;
}

/*
 * Helper for expand and merge extent_cache for wipe_one_reserved_range() to
 * handle wiping a range that exists in cache.
 */
static int _expand_extent_cache(struct cache_tree *tree,
                                struct cache_extent *entry,
                                u64 min_stripe_size, int backward)
{
        struct cache_extent *ce;
        int diff;

        if (entry->size >= min_stripe_size)
                return 0;
        diff = min_stripe_size - entry->size;

        if (backward) {
                ce = prev_cache_extent(entry);
                if (!ce)
                        goto expand_back;
                if (ce->start + ce->size >= entry->start - diff) {
                        /* Directly merge with previous extent */
                        ce->size = entry->start + entry->size - ce->start;
                        remove_cache_extent(tree, entry);
                        free(entry);
                        return 0;
                }
expand_back:
                /* No overlap, normal extent */
                if (entry->start < diff) {
                        error("cannot find space for data chunk layout");
                        return -ENOSPC;
                }
                entry->start -= diff;
                entry->size += diff;
                return 0;
        }
        ce = next_cache_extent(entry);
        if (!ce)
                goto expand_after;
        if (entry->start + entry->size + diff >= ce->start) {
                /* Directly merge with next extent */
                entry->size = ce->start + ce->size - entry->start;
                remove_cache_extent(tree, ce);
                free(ce);
                return 0;
        }
expand_after:
        entry->size += diff;
        return 0;
}

/*
 * Remove one reserve range from given cache tree
 * if min_stripe_size is non-zero, it will ensure for split case,
 * all its split cache extent is no smaller than @min_strip_size / 2.
 */
static int wipe_one_reserved_range(struct cache_tree *tree,
                                   u64 start, u64 len, u64 min_stripe_size,
                                   int ensure_size)
{
        struct cache_extent *cache;
        int ret;

        BUG_ON(ensure_size && min_stripe_size == 0);
        /*
         * The logical here is simplified to handle special cases only
         * So we don't need to consider merge case for ensure_size
         */
        BUG_ON(min_stripe_size && (min_stripe_size < len * 2 ||
               min_stripe_size / 2 < BTRFS_STRIPE_LEN));

        /* Also, wipe range should already be aligned */
        BUG_ON(start != round_down(start, BTRFS_STRIPE_LEN) ||
               start + len != round_up(start + len, BTRFS_STRIPE_LEN));

        min_stripe_size /= 2;

        cache = lookup_cache_extent(tree, start, len);
        if (!cache)
                return 0;

        if (start <= cache->start) {
                /*
                 *      |--------cache---------|
                 * |-wipe-|
                 */
                BUG_ON(start + len <= cache->start);

                /*
                 * The wipe size is smaller than min_stripe_size / 2,
                 * so the result length should still meet min_stripe_size
                 * And no need to do alignment
                 */
                cache->size -= (start + len - cache->start);
                if (cache->size == 0) {
                        remove_cache_extent(tree, cache);
                        free(cache);
                        return 0;
                }

                BUG_ON(ensure_size && cache->size < min_stripe_size);

                cache->start = start + len;
                return 0;
        } else if (start > cache->start && start + len < cache->start +
                   cache->size) {
                /*
                 * |-------cache-----|
                 *      |-wipe-|
                 */
                u64 old_start = cache->start;
                u64 old_len = cache->size;
                u64 insert_start = start + len;
                u64 insert_len;

                cache->size = start - cache->start;
                /* Expand the leading half part if needed */
                if (ensure_size && cache->size < min_stripe_size) {
                        ret = _expand_extent_cache(tree, cache,
                                        min_stripe_size, 1);
                        if (ret < 0)
                                return ret;
                }

                /* And insert the new one */
                insert_len = old_start + old_len - start - len;
                ret = add_merge_cache_extent(tree, insert_start, insert_len);
                if (ret < 0)
                        return ret;

                /* Expand the last half part if needed */
                if (ensure_size && insert_len < min_stripe_size) {
                        cache = lookup_cache_extent(tree, insert_start,
                                                    insert_len);
                        if (!cache || cache->start != insert_start ||
                            cache->size != insert_len)
                                return -ENOENT;
                        ret = _expand_extent_cache(tree, cache,
                                        min_stripe_size, 0);
                }

                return ret;
        }
        /*
         * |----cache-----|
         *              |--wipe-|
         * Wipe len should be small enough and no need to expand the
         * remaining extent
         */
        cache->size = start - cache->start;
        BUG_ON(ensure_size && cache->size < min_stripe_size);
        return 0;
}

/*
 * Remove reserved ranges from given cache_tree
 *
 * It will remove the following ranges
 * 1) 0~1M
 * 2) 2nd superblock, +64K (make sure chunks are 64K aligned)
 * 3) 3rd superblock, +64K
 *
 * @min_stripe must be given for safety check
 * and if @ensure_size is given, it will ensure affected cache_extent will be
 * larger than min_stripe_size
 */
static int wipe_reserved_ranges(struct cache_tree *tree, u64 min_stripe_size,
                                int ensure_size)
{
        int i;
        int ret;

        for (i = 0; i < ARRAY_SIZE(btrfs_reserved_ranges); i++) {
                const struct simple_range *range = &btrfs_reserved_ranges[i];

                ret = wipe_one_reserved_range(tree, range->start, range->len,
                                              min_stripe_size, ensure_size);
                if (ret < 0)
                        return ret;
        }
        return ret;
}

static int calculate_available_space(struct btrfs_convert_context *cctx)
{
        struct cache_tree *used = &cctx->used_space;
        struct cache_tree *data_chunks = &cctx->data_chunks;
        struct cache_tree *free = &cctx->free_space;
        struct cache_extent *cache;
        u64 cur_off = 0;
        /*
         * Twice the minimal chunk size, to allow later wipe_reserved_ranges()
         * works without need to consider overlap
         */
        u64 min_stripe_size = SZ_32M;
        int ret;

        /* Calculate data_chunks */
        for (cache = first_cache_extent(used); cache;
             cache = next_cache_extent(cache)) {
                u64 cur_len;

                if (cache->start + cache->size < cur_off)
                        continue;
                if (cache->start > cur_off + min_stripe_size)
                        cur_off = cache->start;
                cur_len = max(cache->start + cache->size - cur_off,
                              min_stripe_size);
                ret = add_merge_cache_extent(data_chunks, cur_off, cur_len);
                if (ret < 0)
                        goto out;
                cur_off += cur_len;
        }
        /*
         * remove reserved ranges, so we won't ever bother relocating an old
         * filesystem extent to other place.
         */
        ret = wipe_reserved_ranges(data_chunks, min_stripe_size, 1);
        if (ret < 0)
                goto out;

        cur_off = 0;
        /*
         * Calculate free space
         * Always round up the start bytenr, to avoid metadata extent corss
         * stripe boundary, as later mkfs_convert() won't have all the extent
         * allocation check
         */
        for (cache = first_cache_extent(data_chunks); cache;
             cache = next_cache_extent(cache)) {
                if (cache->start < cur_off)
                        continue;
                if (cache->start > cur_off) {
                        u64 insert_start;
                        u64 len;

                        len = cache->start - round_up(cur_off,
                                                      BTRFS_STRIPE_LEN);
                        insert_start = round_up(cur_off, BTRFS_STRIPE_LEN);

                        ret = add_merge_cache_extent(free, insert_start, len);
                        if (ret < 0)
                                goto out;
                }
                cur_off = cache->start + cache->size;
        }
        /* Don't forget the last range */
        if (cctx->total_bytes > cur_off) {
                u64 len = cctx->total_bytes - cur_off;
                u64 insert_start;

                insert_start = round_up(cur_off, BTRFS_STRIPE_LEN);

                ret = add_merge_cache_extent(free, insert_start, len);
                if (ret < 0)
                        goto out;
        }

        /* Remove reserved bytes */
        ret = wipe_reserved_ranges(free, min_stripe_size, 0);
out:
        return ret;
}

/*
 * Read used space, and since we have the used space,
 * calcuate data_chunks and free for later mkfs
 */
static int convert_read_used_space(struct btrfs_convert_context *cctx)
{
        int ret;

        ret = cctx->convert_ops->read_used_space(cctx);
        if (ret)
                return ret;

        ret = calculate_available_space(cctx);
        return ret;
}

/*
 * Create the fs image file of old filesystem.
 *
 * This is completely fs independent as we have cctx->used, only
 * need to create file extents pointing to all the positions.
 */
static int create_image(struct btrfs_root *root,
                           struct btrfs_mkfs_config *cfg,
                           struct btrfs_convert_context *cctx, int fd,
                           u64 size, char *name, u32 convert_flags)
{
        struct btrfs_inode_item buf;
        struct btrfs_trans_handle *trans;
        struct btrfs_path path;
        struct btrfs_key key;
        struct cache_extent *cache;
        struct cache_tree used_tmp;
        u64 cur;
        u64 ino;
        u64 flags = BTRFS_INODE_READONLY;
        int ret;

        if (!(convert_flags & CONVERT_FLAG_DATACSUM))
                flags |= BTRFS_INODE_NODATASUM;

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

        cache_tree_init(&used_tmp);
        btrfs_init_path(&path);

        ret = btrfs_find_free_objectid(trans, root, BTRFS_FIRST_FREE_OBJECTID,
                                       &ino);
        if (ret < 0)
                goto out;
        ret = btrfs_new_inode(trans, root, ino, 0400 | S_IFREG);
        if (ret < 0)
                goto out;
        ret = btrfs_change_inode_flags(trans, root, ino, flags);
        if (ret < 0)
                goto out;
        ret = btrfs_add_link(trans, root, ino, BTRFS_FIRST_FREE_OBJECTID, name,
                             strlen(name), BTRFS_FT_REG_FILE, NULL, 1, 0);
        if (ret < 0)
                goto out;

        key.objectid = ino;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;

        ret = btrfs_search_slot(trans, root, &key, &path, 0, 1);
        if (ret) {
                ret = (ret > 0 ? -ENOENT : ret);
                goto out;
        }
        read_extent_buffer(path.nodes[0], &buf,
                        btrfs_item_ptr_offset(path.nodes[0], path.slots[0]),
                        sizeof(buf));
        btrfs_release_path(&path);

        /*
         * Create a new used space cache, which doesn't contain the reserved
         * range
         */
        for (cache = first_cache_extent(&cctx->used_space); cache;
             cache = next_cache_extent(cache)) {
                ret = add_cache_extent(&used_tmp, cache->start, cache->size);
                if (ret < 0)
                        goto out;
        }
        ret = wipe_reserved_ranges(&used_tmp, 0, 0);
        if (ret < 0)
                goto out;

        /*
         * Start from 1M, as 0~1M is reserved, and create_image_file_range()
         * can't handle bytenr 0(will consider it as a hole)
         */
        cur = SZ_1M;
        while (cur < size) {
                u64 len = size - cur;

                ret = create_image_file_range(trans, root, &used_tmp,
                                                &buf, ino, cur, &len,
                                                convert_flags);
                if (ret < 0)
                        goto out;
                cur += len;
        }
        /* Handle the reserved ranges */
        ret = migrate_reserved_ranges(trans, root, &cctx->used_space, &buf, fd,
                        ino, cfg->num_bytes, convert_flags);

        key.objectid = ino;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(trans, root, &key, &path, 0, 1);
        if (ret) {
                ret = (ret > 0 ? -ENOENT : ret);
                goto out;
        }
        btrfs_set_stack_inode_size(&buf, cfg->num_bytes);
        write_extent_buffer(path.nodes[0], &buf,
                        btrfs_item_ptr_offset(path.nodes[0], path.slots[0]),
                        sizeof(buf));
out:
        free_extent_cache_tree(&used_tmp);
        btrfs_release_path(&path);
        btrfs_commit_transaction(trans, root);
        return ret;
}

static int create_subvol(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root, u64 root_objectid)
{
        struct extent_buffer *tmp;
        struct btrfs_root *new_root;
        struct btrfs_key key;
        struct btrfs_root_item root_item;
        int ret;

        ret = btrfs_copy_root(trans, root, root->node, &tmp,
                              root_objectid);
        if (ret)
                return ret;

        memcpy(&root_item, &root->root_item, sizeof(root_item));
        btrfs_set_root_bytenr(&root_item, tmp->start);
        btrfs_set_root_level(&root_item, btrfs_header_level(tmp));
        btrfs_set_root_generation(&root_item, trans->transid);
        free_extent_buffer(tmp);

        key.objectid = root_objectid;
        key.type = BTRFS_ROOT_ITEM_KEY;
        key.offset = trans->transid;
        ret = btrfs_insert_root(trans, root->fs_info->tree_root,
                                &key, &root_item);

        key.offset = (u64)-1;
        new_root = btrfs_read_fs_root(root->fs_info, &key);
        if (!new_root || IS_ERR(new_root)) {
                error("unable to fs read root: %lu", PTR_ERR(new_root));
                return PTR_ERR(new_root);
        }

        ret = btrfs_make_root_dir(trans, new_root, BTRFS_FIRST_FREE_OBJECTID);

        return ret;
}

/*
 * New make_btrfs() has handle system and meta chunks quite well.
 * So only need to add remaining data chunks.
 */
static int make_convert_data_block_groups(struct btrfs_trans_handle *trans,
                                          struct btrfs_fs_info *fs_info,
                                          struct btrfs_mkfs_config *cfg,
                                          struct btrfs_convert_context *cctx)
{
        struct btrfs_root *extent_root = fs_info->extent_root;
        struct cache_tree *data_chunks = &cctx->data_chunks;
        struct cache_extent *cache;
        u64 max_chunk_size;
        int ret = 0;

        /*
         * Don't create data chunk over 10% of the convert device
         * And for single chunk, don't create chunk larger than 1G.
         */
        max_chunk_size = cfg->num_bytes / 10;
        max_chunk_size = min((u64)(SZ_1G), max_chunk_size);
        max_chunk_size = round_down(max_chunk_size,
                                    extent_root->fs_info->sectorsize);

        for (cache = first_cache_extent(data_chunks); cache;
             cache = next_cache_extent(cache)) {
                u64 cur = cache->start;

                while (cur < cache->start + cache->size) {
                        u64 len;
                        u64 cur_backup = cur;

                        len = min(max_chunk_size,
                                  cache->start + cache->size - cur);
                        ret = btrfs_alloc_data_chunk(trans, fs_info,
                                        &cur_backup, len,
                                        BTRFS_BLOCK_GROUP_DATA, 1);
                        if (ret < 0)
                                break;
                        ret = btrfs_make_block_group(trans, fs_info, 0,
                                        BTRFS_BLOCK_GROUP_DATA,
                                        BTRFS_FIRST_CHUNK_TREE_OBJECTID,
                                        cur, len);
                        if (ret < 0)
                                break;
                        cur += len;
                }
        }
        return ret;
}

/*
 * Init the temp btrfs to a operational status.
 *
 * It will fix the extent usage accounting(XXX: Do we really need?) and
 * insert needed data chunks, to ensure all old fs data extents are covered
 * by DATA chunks, preventing wrong chunks are allocated.
 *
 * And also create convert image subvolume and relocation tree.
 * (XXX: Not need again?)
 * But the convert image subvolume is *NOT* linked to fs tree yet.
 */
static int init_btrfs(struct btrfs_mkfs_config *cfg, struct btrfs_root *root,
                         struct btrfs_convert_context *cctx, u32 convert_flags)
{
        struct btrfs_key location;
        struct btrfs_trans_handle *trans;
        struct btrfs_fs_info *fs_info = root->fs_info;
        int ret;

        /*
         * Don't alloc any metadata/system chunk, as we don't want
         * any meta/sys chunk allcated before all data chunks are inserted.
         * Or we screw up the chunk layout just like the old implement.
         */
        fs_info->avoid_sys_chunk_alloc = 1;
        fs_info->avoid_meta_chunk_alloc = 1;
        trans = btrfs_start_transaction(root, 1);
        if (IS_ERR(trans)) {
                error("unable to start transaction");
                ret = PTR_ERR(trans);
                goto err;
        }
        ret = btrfs_fix_block_accounting(trans, root);
        if (ret)
                goto err;
        ret = make_convert_data_block_groups(trans, fs_info, cfg, cctx);
        if (ret)
                goto err;
        ret = btrfs_make_root_dir(trans, fs_info->tree_root,
                                  BTRFS_ROOT_TREE_DIR_OBJECTID);
        if (ret)
                goto err;
        memcpy(&location, &root->root_key, sizeof(location));
        location.offset = (u64)-1;
        ret = btrfs_insert_dir_item(trans, fs_info->tree_root, "default", 7,
                                btrfs_super_root_dir(fs_info->super_copy),
                                &location, BTRFS_FT_DIR, 0);
        if (ret)
                goto err;
        ret = btrfs_insert_inode_ref(trans, fs_info->tree_root, "default", 7,
                                location.objectid,
                                btrfs_super_root_dir(fs_info->super_copy), 0);
        if (ret)
                goto err;
        btrfs_set_root_dirid(&fs_info->fs_root->root_item,
                             BTRFS_FIRST_FREE_OBJECTID);

        /* subvol for fs image file */
        ret = create_subvol(trans, root, CONV_IMAGE_SUBVOL_OBJECTID);
        if (ret < 0) {
                error("failed to create subvolume image root: %d", ret);
                goto err;
        }
        /* subvol for data relocation tree */
        ret = create_subvol(trans, root, BTRFS_DATA_RELOC_TREE_OBJECTID);
        if (ret < 0) {
                error("failed to create DATA_RELOC root: %d", ret);
                goto err;
        }

        ret = btrfs_commit_transaction(trans, root);
        fs_info->avoid_sys_chunk_alloc = 0;
        fs_info->avoid_meta_chunk_alloc = 0;
err:
        return ret;
}

/*
 * Migrate super block to its default position and zero 0 ~ 16k
 */
static int migrate_super_block(int fd, u64 old_bytenr)
{
        int ret;
        struct extent_buffer *buf;
        struct btrfs_super_block *super;
        u32 len;
        u32 bytenr;

        buf = malloc(sizeof(*buf) + BTRFS_SUPER_INFO_SIZE);
        if (!buf)
                return -ENOMEM;

        buf->len = BTRFS_SUPER_INFO_SIZE;
        ret = pread(fd, buf->data, BTRFS_SUPER_INFO_SIZE, old_bytenr);
        if (ret != BTRFS_SUPER_INFO_SIZE)
                goto fail;

        super = (struct btrfs_super_block *)buf->data;
        BUG_ON(btrfs_super_bytenr(super) != old_bytenr);
        btrfs_set_super_bytenr(super, BTRFS_SUPER_INFO_OFFSET);

        csum_tree_block_size(buf, BTRFS_CRC32_SIZE, 0);
        ret = pwrite(fd, buf->data, BTRFS_SUPER_INFO_SIZE,
                BTRFS_SUPER_INFO_OFFSET);
        if (ret != BTRFS_SUPER_INFO_SIZE)
                goto fail;

        ret = fsync(fd);
        if (ret)
                goto fail;

        memset(buf->data, 0, BTRFS_SUPER_INFO_SIZE);
        for (bytenr = 0; bytenr < BTRFS_SUPER_INFO_OFFSET; ) {
                len = BTRFS_SUPER_INFO_OFFSET - bytenr;
                if (len > BTRFS_SUPER_INFO_SIZE)
                        len = BTRFS_SUPER_INFO_SIZE;
                ret = pwrite(fd, buf->data, len, bytenr);
                if (ret != len) {
                        fprintf(stderr, "unable to zero fill device\n");
                        break;
                }
                bytenr += len;
        }
        ret = 0;
        fsync(fd);
fail:
        free(buf);
        if (ret > 0)
                ret = -1;
        return ret;
}

static int convert_open_fs(const char *devname,
                           struct btrfs_convert_context *cctx)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(convert_operations); i++) {
                int ret = convert_operations[i]->open_fs(cctx, devname);

                if (ret == 0) {
                        cctx->convert_ops = convert_operations[i];
                        return ret;
                }
        }

        error("no file system found to convert");
        return -1;
}

static int do_convert(const char *devname, u32 convert_flags, u32 nodesize,
                const char *fslabel, int progress, u64 features)
{
        int ret;
        int fd = -1;
        u32 blocksize;
        u64 total_bytes;
        struct btrfs_root *root;
        struct btrfs_root *image_root;
        struct btrfs_convert_context cctx;
        struct btrfs_key key;
        char subvol_name[SOURCE_FS_NAME_LEN + 8];
        struct task_ctx ctx;
        char features_buf[64];
        struct btrfs_mkfs_config mkfs_cfg;

        init_convert_context(&cctx);
        ret = convert_open_fs(devname, &cctx);
        if (ret)
                goto fail;
        ret = convert_check_state(&cctx);
        if (ret)
                warning(
                "source filesystem is not clean, running filesystem check is recommended");
        ret = convert_read_used_space(&cctx);
        if (ret)
                goto fail;

        blocksize = cctx.blocksize;
        total_bytes = (u64)blocksize * (u64)cctx.block_count;
        if (blocksize < 4096) {
                error("block size is too small: %u < 4096", blocksize);
                goto fail;
        }
        if (btrfs_check_nodesize(nodesize, blocksize, features))
                goto fail;
        fd = open(devname, O_RDWR);
        if (fd < 0) {
                error("unable to open %s: %s", devname, strerror(errno));
                goto fail;
        }
        btrfs_parse_features_to_string(features_buf, features);
        if (features == BTRFS_MKFS_DEFAULT_FEATURES)
                strcat(features_buf, " (default)");

        printf("create btrfs filesystem:\n");
        printf("\tblocksize: %u\n", blocksize);
        printf("\tnodesize:  %u\n", nodesize);
        printf("\tfeatures:  %s\n", features_buf);

        memset(&mkfs_cfg, 0, sizeof(mkfs_cfg));
        mkfs_cfg.label = cctx.volume_name;
        mkfs_cfg.num_bytes = total_bytes;
        mkfs_cfg.nodesize = nodesize;
        mkfs_cfg.sectorsize = blocksize;
        mkfs_cfg.stripesize = blocksize;
        mkfs_cfg.features = features;

        ret = make_convert_btrfs(fd, &mkfs_cfg, &cctx);
        if (ret) {
                error("unable to create initial ctree: %s", strerror(-ret));
                goto fail;
        }

        root = open_ctree_fd(fd, devname, mkfs_cfg.super_bytenr,
                             OPEN_CTREE_WRITES | OPEN_CTREE_FS_PARTIAL);
        if (!root) {
                error("unable to open ctree");
                goto fail;
        }
        ret = init_btrfs(&mkfs_cfg, root, &cctx, convert_flags);
        if (ret) {
                error("unable to setup the root tree: %d", ret);
                goto fail;
        }

        printf("creating %s image file\n", cctx.convert_ops->name);
        snprintf(subvol_name, sizeof(subvol_name), "%s_saved",
                        cctx.convert_ops->name);
        key.objectid = CONV_IMAGE_SUBVOL_OBJECTID;
        key.offset = (u64)-1;
        key.type = BTRFS_ROOT_ITEM_KEY;
        image_root = btrfs_read_fs_root(root->fs_info, &key);
        if (!image_root) {
                error("unable to create image subvolume");
                goto fail;
        }
        ret = create_image(image_root, &mkfs_cfg, &cctx, fd,
                              mkfs_cfg.num_bytes, "image",
                              convert_flags);
        if (ret) {
                error("failed to create %s/image: %d", subvol_name, ret);
                goto fail;
        }

        printf("creating btrfs metadata\n");
        ret = pthread_mutex_init(&ctx.mutex, NULL);
        if (ret) {
                error("failed to initialize mutex: %d", ret);
                goto fail;
        }
        ctx.max_copy_inodes = (cctx.inodes_count - cctx.free_inodes_count);
        ctx.cur_copy_inodes = 0;

        if (progress) {
                ctx.info = task_init(print_copied_inodes, after_copied_inodes,
                                     &ctx);
                task_start(ctx.info);
        }
        ret = copy_inodes(&cctx, root, convert_flags, &ctx);
        if (ret) {
                error("error during copy_inodes %d", ret);
                goto fail;
        }
        if (progress) {
                task_stop(ctx.info);
                task_deinit(ctx.info);
        }

        image_root = btrfs_mksubvol(root, subvol_name,
                                    CONV_IMAGE_SUBVOL_OBJECTID, true);
        if (!image_root) {
                error("unable to link subvolume %s", subvol_name);
                goto fail;
        }

        memset(root->fs_info->super_copy->label, 0, BTRFS_LABEL_SIZE);
        if (convert_flags & CONVERT_FLAG_COPY_LABEL) {
                __strncpy_null(root->fs_info->super_copy->label,
                                cctx.volume_name, BTRFS_LABEL_SIZE - 1);
                printf("copy label '%s'\n", root->fs_info->super_copy->label);
        } else if (convert_flags & CONVERT_FLAG_SET_LABEL) {
                strcpy(root->fs_info->super_copy->label, fslabel);
                printf("set label to '%s'\n", fslabel);
        }

        ret = close_ctree(root);
        if (ret) {
                error("close_ctree failed: %d", ret);
                goto fail;
        }
        convert_close_fs(&cctx);
        clean_convert_context(&cctx);

        /*
         * If this step succeed, we get a mountable btrfs. Otherwise
         * the source fs is left unchanged.
         */
        ret = migrate_super_block(fd, mkfs_cfg.super_bytenr);
        if (ret) {
                error("unable to migrate super block: %d", ret);
                goto fail;
        }

        root = open_ctree_fd(fd, devname, 0,
                        OPEN_CTREE_WRITES | OPEN_CTREE_FS_PARTIAL);
        if (!root) {
                error("unable to open ctree for finalization");
                goto fail;
        }
        root->fs_info->finalize_on_close = 1;
        close_ctree(root);
        close(fd);

        printf("conversion complete\n");
        return 0;
fail:
        clean_convert_context(&cctx);
        if (fd != -1)
                close(fd);
        warning(
"an error occurred during conversion, filesystem is partially created but not finalized and not mountable");
        return -1;
}

/*
 * Read out data of convert image which is in btrfs reserved ranges so we can
 * use them to overwrite the ranges during rollback.
 */
static int read_reserved_ranges(struct btrfs_root *root, u64 ino,
                                u64 total_bytes, char *reserved_ranges[])
{
        int i;
        int ret = 0;

        for (i = 0; i < ARRAY_SIZE(btrfs_reserved_ranges); i++) {
                const struct simple_range *range = &btrfs_reserved_ranges[i];

                if (range->start + range->len >= total_bytes)
                        break;
                ret = btrfs_read_file(root, ino, range->start, range->len,
                                      reserved_ranges[i]);
                if (ret < range->len) {
                        error(
        "failed to read data of convert image, offset=%llu len=%llu ret=%d",
                              range->start, range->len, ret);
                        if (ret >= 0)
                                ret = -EIO;
                        break;
                }
                ret = 0;
        }
        return ret;
}

static bool is_subset_of_reserved_ranges(u64 start, u64 len)
{
        int i;
        bool ret = false;

        for (i = 0; i < ARRAY_SIZE(btrfs_reserved_ranges); i++) {
                const struct simple_range *range = &btrfs_reserved_ranges[i];

                if (start >= range->start && start + len <= range_end(range)) {
                        ret = true;
                        break;
                }
        }
        return ret;
}

static bool is_chunk_direct_mapped(struct btrfs_fs_info *fs_info, u64 start)
{
        struct cache_extent *ce;
        struct map_lookup *map;
        bool ret = false;

        ce = search_cache_extent(&fs_info->mapping_tree.cache_tree, start);
        if (!ce)
                goto out;
        if (ce->start > start || ce->start + ce->size < start)
                goto out;

        map = container_of(ce, struct map_lookup, ce);

        /* Not SINGLE chunk */
        if (map->num_stripes != 1)
                goto out;

        /* Chunk's logical doesn't match with phisical, not 1:1 mapped */
        if (map->ce.start != map->stripes[0].physical)
                goto out;
        ret = true;
out:
        return ret;
}

/*
 * Iterate all file extents of the convert image.
 *
 * All file extents except ones in btrfs_reserved_ranges must be mapped 1:1
 * on disk. (Means thier file_offset must match their on disk bytenr)
 *
 * File extents in reserved ranges can be relocated to other place, and in
 * that case we will read them out for later use.
 */
static int check_convert_image(struct btrfs_root *image_root, u64 ino,
                               u64 total_size, char *reserved_ranges[])
{
        struct btrfs_key key;
        struct btrfs_path path;
        struct btrfs_fs_info *fs_info = image_root->fs_info;
        u64 checked_bytes = 0;
        int ret;

        key.objectid = ino;
        key.offset = 0;
        key.type = BTRFS_EXTENT_DATA_KEY;

        btrfs_init_path(&path);
        ret = btrfs_search_slot(NULL, image_root, &key, &path, 0, 0);
        /*
         * It's possible that some fs doesn't store any (including sb)
         * data into 0~1M range, and NO_HOLES is enabled.
         *
         * So we only need to check if ret < 0
         */
        if (ret < 0) {
                error("failed to iterate file extents at offset 0: %s",
                        strerror(-ret));
                btrfs_release_path(&path);
                return ret;
        }

        /* Loop from the first file extents */
        while (1) {
                struct btrfs_file_extent_item *fi;
                struct extent_buffer *leaf = path.nodes[0];
                u64 disk_bytenr;
                u64 file_offset;
                u64 ram_bytes;
                int slot = path.slots[0];

                if (slot >= btrfs_header_nritems(leaf))
                        goto next;
                btrfs_item_key_to_cpu(leaf, &key, slot);

                /*
                 * Iteration is done, exit normally, we have extra check out of
                 * the loop
                 */
                if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY) {
                        ret = 0;
                        break;
                }
                file_offset = key.offset;
                fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
                if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_REG) {
                        ret = -EINVAL;
                        error(
                "ino %llu offset %llu doesn't have a regular file extent",
                                ino, file_offset);
                        break;
                }
                if (btrfs_file_extent_compression(leaf, fi) ||
                    btrfs_file_extent_encryption(leaf, fi) ||
                    btrfs_file_extent_other_encoding(leaf, fi)) {
                        ret = -EINVAL;
                        error(
                        "ino %llu offset %llu doesn't have a plain file extent",
                                ino, file_offset);
                        break;
                }

                disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
                ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi);

                checked_bytes += ram_bytes;
                /* Skip hole */
                if (disk_bytenr == 0)
                        goto next;

                /*
                 * Most file extents must be 1:1 mapped, which means 2 things:
                 * 1) File extent file offset == disk_bytenr
                 * 2) That data chunk's logical == chunk's physical
                 *
                 * So file extent's file offset == physical position on disk.
                 *
                 * And after rolling back btrfs reserved range, other part
                 * remains what old fs used to be.
                 */
                if (file_offset != disk_bytenr ||
                    !is_chunk_direct_mapped(fs_info, disk_bytenr)) {
                        /*
                         * Only file extent in btrfs reserved ranges are
                         * allowed to be non-1:1 mapped
                         */
                        if (!is_subset_of_reserved_ranges(file_offset,
                                                        ram_bytes)) {
                                ret = -EINVAL;
                                error(
                "ino %llu offset %llu file extent should not be relocated",
                                        ino, file_offset);
                                break;
                        }
                }
next:
                ret = btrfs_next_item(image_root, &path);
                if (ret) {
                        if (ret > 0)
                                ret = 0;
                        break;
                }
        }
        btrfs_release_path(&path);
        if (ret)
                return ret;
        /*
         * For HOLES mode (without NO_HOLES), we must ensure file extents
         * cover the whole range of the image
         */
        if (!ret && !btrfs_fs_incompat(fs_info, NO_HOLES)) {
                if (checked_bytes != total_size) {
                        ret = -EINVAL;
                        error("inode %llu has some file extents not checked",
                                ino);
                        return ret;
                }
        }

        /* So far so good, read old data located in btrfs reserved ranges */
        ret = read_reserved_ranges(image_root, ino, total_size,
                                   reserved_ranges);
        return ret;
}

/*
 * btrfs rollback is just reverted convert:
 * |<---------------Btrfs fs------------------------------>|
 * |<-   Old data chunk  ->|< new chunk (D/M/S)>|<- ODC  ->|
 * |<-Old-FE->| |<-Old-FE->|<- Btrfs extents  ->|<-Old-FE->|
 *                           ||
 *                           \/
 * |<------------------Old fs----------------------------->|
 * |<- used ->| |<- used ->|                    |<- used ->|
 *
 * However things are much easier than convert, we don't really need to
 * do the complex space calculation, but only to handle btrfs reserved space
 *
 * |<---------------------------Btrfs fs----------------------------->|
 * |   RSV 1   |  | Old  |   |    RSV 2  | | Old  | |   RSV 3   |
 * |   0~1M    |  | Fs   |   | SB2 + 64K | | Fs   | | SB3 + 64K |
 *
 * On the other hand, the converted fs image in btrfs is a completely
 * valid old fs.
 *
 * |<-----------------Converted fs image in btrfs-------------------->|
 * |   RSV 1   |  | Old  |   |    RSV 2  | | Old  | |   RSV 3   |
 * | Relocated |  | Fs   |   | Relocated | | Fs   | | Relocated |
 *
 * Used space in fs image should be at the same physical position on disk.
 * We only need to recover the data in reserved ranges, so the whole
 * old fs is back.
 *
 * The idea to rollback is also straightforward, we just "read" out the data
 * of reserved ranges, and write them back to there they should be.
 * Then the old fs is back.
 */
static int do_rollback(const char *devname)
{
        struct btrfs_root *root;
        struct btrfs_root *image_root;
        struct btrfs_fs_info *fs_info;
        struct btrfs_key key;
        struct btrfs_path path;
        struct btrfs_dir_item *dir;
        struct btrfs_inode_item *inode_item;
        char *image_name = "image";
        char *reserved_ranges[ARRAY_SIZE(btrfs_reserved_ranges)] = { NULL };
        u64 total_bytes;
        u64 fsize;
        u64 root_dir;
        u64 ino;
        int fd = -1;
        int ret;
        int i;

        for (i = 0; i < ARRAY_SIZE(btrfs_reserved_ranges); i++) {
                const struct simple_range *range = &btrfs_reserved_ranges[i];

                reserved_ranges[i] = calloc(1, range->len);
                if (!reserved_ranges[i]) {
                        ret = -ENOMEM;
                        goto free_mem;
                }
        }
        fd = open(devname, O_RDWR);
        if (fd < 0) {
                error("unable to open %s: %s", devname, strerror(errno));
                ret = -EIO;
                goto free_mem;
        }
        fsize = lseek(fd, 0, SEEK_END);

        /*
         * For rollback, we don't really need to write anything so open it
         * read-only.  The write part will happen after we close the
         * filesystem.
         */
        root = open_ctree_fd(fd, devname, 0, 0);
        if (!root) {
                error("unable to open ctree");
                ret = -EIO;
                goto free_mem;
        }
        fs_info = root->fs_info;

        /*
         * Search root backref first, or after subvolume deletion (orphan),
         * we can still rollback the image.
         */
        key.objectid = CONV_IMAGE_SUBVOL_OBJECTID;
        key.type = BTRFS_ROOT_BACKREF_KEY;
        key.offset = BTRFS_FS_TREE_OBJECTID;
        btrfs_init_path(&path);
        ret = btrfs_search_slot(NULL, fs_info->tree_root, &key, &path, 0, 0);
        btrfs_release_path(&path);
        if (ret > 0) {
                error("unable to find source fs image subvolume, is it deleted?");
                ret = -ENOENT;
                goto close_fs;
        } else if (ret < 0) {
                error("failed to find source fs image subvolume: %s",
                        strerror(-ret));
                goto close_fs;
        }

        /* Search convert subvolume */
        key.objectid = CONV_IMAGE_SUBVOL_OBJECTID;
        key.type = BTRFS_ROOT_ITEM_KEY;
        key.offset = (u64)-1;
        image_root = btrfs_read_fs_root(fs_info, &key);
        if (IS_ERR(image_root)) {
                ret = PTR_ERR(image_root);
                error("failed to open convert image subvolume: %s",
                        strerror(-ret));
                goto close_fs;
        }

        /* Search the image file */
        root_dir = btrfs_root_dirid(&image_root->root_item);
        dir = btrfs_lookup_dir_item(NULL, image_root, &path, root_dir,
                        image_name, strlen(image_name), 0);

        if (!dir || IS_ERR(dir)) {
                btrfs_release_path(&path);
                if (dir)
                        ret = PTR_ERR(dir);
                else
                        ret = -ENOENT;
                error("failed to locate file %s: %s", image_name,
                        strerror(-ret));
                goto close_fs;
        }
        btrfs_dir_item_key_to_cpu(path.nodes[0], dir, &key);
        btrfs_release_path(&path);

        /* Get total size of the original image */
        ino = key.objectid;

        ret = btrfs_lookup_inode(NULL, image_root, &path, &key, 0);

        if (ret < 0) {
                btrfs_release_path(&path);
                error("unable to find inode %llu: %s", ino, strerror(-ret));
                goto close_fs;
        }
        inode_item = btrfs_item_ptr(path.nodes[0], path.slots[0],
                                    struct btrfs_inode_item);
        total_bytes = btrfs_inode_size(path.nodes[0], inode_item);
        btrfs_release_path(&path);

        /* Check if we can rollback the image */
        ret = check_convert_image(image_root, ino, total_bytes, reserved_ranges);
        if (ret < 0) {
                error("old fs image can't be rolled back");
                goto close_fs;
        }
close_fs:
        btrfs_release_path(&path);
        close_ctree_fs_info(fs_info);
        if (ret)
                goto free_mem;

        /*
         * Everything is OK, just write back old fs data into btrfs reserved
         * ranges
         *
         * Here, we starts from the backup blocks first, so if something goes
         * wrong, the fs is still mountable
         */

        for (i = ARRAY_SIZE(btrfs_reserved_ranges) - 1; i >= 0; i--) {
                u64 real_size;
                const struct simple_range *range = &btrfs_reserved_ranges[i];

                if (range_end(range) >= fsize)
                        continue;

                real_size = min(range_end(range), fsize) - range->start;
                ret = pwrite(fd, reserved_ranges[i], real_size, range->start);
                if (ret < real_size) {
                        if (ret < 0)
                                ret = -errno;
                        else
                                ret = -EIO;
                        error("failed to recover range [%llu, %llu): %s",
                              range->start, real_size, strerror(-ret));
                        goto free_mem;
                }
                ret = 0;
        }

free_mem:
        for (i = 0; i < ARRAY_SIZE(btrfs_reserved_ranges); i++)
                free(reserved_ranges[i]);
        if (ret)
                error("rollback failed");
        else
                printf("rollback succeeded\n");
        return ret;
}

static void print_usage(void)
{
        printf("usage: btrfs-convert [options] device\n");
        printf("options:\n");
        printf("\t-d|--no-datasum        disable data checksum, sets NODATASUM\n");
        printf("\t-i|--no-xattr          ignore xattrs and ACLs\n");
        printf("\t-n|--no-inline         disable inlining of small files to metadata\n");
        printf("\t-N|--nodesize SIZE     set filesystem metadata nodesize\n");
        printf("\t-r|--rollback          roll back to the original filesystem\n");
        printf("\t-l|--label LABEL       set filesystem label\n");
        printf("\t-L|--copy-label        use label from converted filesystem\n");
        printf("\t-p|--progress          show converting progress (default)\n");
        printf("\t-O|--features LIST     comma separated list of filesystem features\n");
        printf("\t--no-progress          show only overview, not the detailed progress\n");
        printf("\n");
        printf("Supported filesystems:\n");
        printf("\text2/3/4: %s\n", BTRFSCONVERT_EXT2 ? "yes" : "no");
        printf("\treiserfs: %s\n", BTRFSCONVERT_REISERFS ? "yes" : "no");
}

int main(int argc, char *argv[])
{
        int ret;
        int packing = 1;
        int noxattr = 0;
        int datacsum = 1;
        u32 nodesize = max_t(u32, sysconf(_SC_PAGESIZE),
                        BTRFS_MKFS_DEFAULT_NODE_SIZE);
        int rollback = 0;
        int copylabel = 0;
        int usage_error = 0;
        int progress = 1;
        char *file;
        char fslabel[BTRFS_LABEL_SIZE];
        u64 features = BTRFS_MKFS_DEFAULT_FEATURES;

        while(1) {
                enum { GETOPT_VAL_NO_PROGRESS = 256 };
                static const struct option long_options[] = {
                        { "no-progress", no_argument, NULL,
                                GETOPT_VAL_NO_PROGRESS },
                        { "no-datasum", no_argument, NULL, 'd' },
                        { "no-inline", no_argument, NULL, 'n' },
                        { "no-xattr", no_argument, NULL, 'i' },
                        { "rollback", no_argument, NULL, 'r' },
                        { "features", required_argument, NULL, 'O' },
                        { "progress", no_argument, NULL, 'p' },
                        { "label", required_argument, NULL, 'l' },
                        { "copy-label", no_argument, NULL, 'L' },
                        { "nodesize", required_argument, NULL, 'N' },
                        { "help", no_argument, NULL, GETOPT_VAL_HELP},
                        { NULL, 0, NULL, 0 }
                };
                int c = getopt_long(argc, argv, "dinN:rl:LpO:", long_options, NULL);

                if (c < 0)
                        break;
                switch(c) {
                        case 'd':
                                datacsum = 0;
                                break;
                        case 'i':
                                noxattr = 1;
                                break;
                        case 'n':
                                packing = 0;
                                break;
                        case 'N':
                                nodesize = parse_size(optarg);
                                break;
                        case 'r':
                                rollback = 1;
                                break;
                        case 'l':
                                copylabel = CONVERT_FLAG_SET_LABEL;
                                if (strlen(optarg) >= BTRFS_LABEL_SIZE) {
                                        warning(
                                        "label too long, trimmed to %d bytes",
                                                BTRFS_LABEL_SIZE - 1);
                                }
                                __strncpy_null(fslabel, optarg, BTRFS_LABEL_SIZE - 1);
                                break;
                        case 'L':
                                copylabel = CONVERT_FLAG_COPY_LABEL;
                                break;
                        case 'p':
                                progress = 1;
                                break;
                        case 'O': {
                                char *orig = strdup(optarg);
                                char *tmp = orig;

                                tmp = btrfs_parse_fs_features(tmp, &features);
                                if (tmp) {
                                        error("unrecognized filesystem feature: %s",
                                                        tmp);
                                        free(orig);
                                        exit(1);
                                }
                                free(orig);
                                if (features & BTRFS_FEATURE_LIST_ALL) {
                                        btrfs_list_all_fs_features(
                                                ~BTRFS_CONVERT_ALLOWED_FEATURES);
                                        exit(0);
                                }
                                if (features & ~BTRFS_CONVERT_ALLOWED_FEATURES) {
                                        char buf[64];

                                        btrfs_parse_features_to_string(buf,
                                                features & ~BTRFS_CONVERT_ALLOWED_FEATURES);
                                        error("features not allowed for convert: %s",
                                                buf);
                                        exit(1);
                                }

                                break;
                                }
                        case GETOPT_VAL_NO_PROGRESS:
                                progress = 0;
                                break;
                        case GETOPT_VAL_HELP:
                        default:
                                print_usage();
                                return c != GETOPT_VAL_HELP;
                }
        }
        set_argv0(argv);
        if (check_argc_exact(argc - optind, 1)) {
                print_usage();
                return 1;
        }

        if (rollback && (!datacsum || noxattr || !packing)) {
                fprintf(stderr,
                        "Usage error: -d, -i, -n options do not apply to rollback\n");
                usage_error++;
        }

        if (usage_error) {
                print_usage();
                return 1;
        }

        file = argv[optind];
        ret = check_mounted(file);
        if (ret < 0) {
                error("could not check mount status: %s", strerror(-ret));
                return 1;
        } else if (ret) {
                error("%s is mounted", file);
                return 1;
        }

        if (rollback) {
                ret = do_rollback(file);
        } else {
                u32 cf = 0;

                cf |= datacsum ? CONVERT_FLAG_DATACSUM : 0;
                cf |= packing ? CONVERT_FLAG_INLINE_DATA : 0;
                cf |= noxattr ? 0 : CONVERT_FLAG_XATTR;
                cf |= copylabel;
                ret = do_convert(file, cf, nodesize, fslabel, progress, features);
        }
        if (ret)
                return 1;
        return 0;
}