From 619104ba453ad0965660d643f64ffbeb721906f5 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Wed, 30 Mar 2022 15:31:06 +0100 Subject: [PATCH] btrfs: move common NOCOW checks against a file extent into a helper Verifying if we can do a NOCOW write against a range fully or partially covered by a file extent item requires verifying several constraints, and these are currently duplicated at two different places: can_nocow_extent() and run_delalloc_nocow(). This change moves those checks into a common helper function to avoid duplication. It adds some comments and also preserves all existing behaviour like for example can_nocow_extent() treating errors from the calls to btrfs_cross_ref_exist() and csum_exist_in_range() as meaning we can not NOCOW, instead of propagating the error back to the caller. That specific behaviour is questionable but also reasonable to some degree. Signed-off-by: Filipe Manana Signed-off-by: David Sterba --- fs/btrfs/inode.c | 427 ++++++++++++++++++++++++++++--------------------------- 1 file changed, 215 insertions(+), 212 deletions(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 77fd450..de3dd78 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -1617,6 +1617,141 @@ static int fallback_to_cow(struct btrfs_inode *inode, struct page *locked_page, nr_written, 1); } +struct can_nocow_file_extent_args { + /* Input fields. */ + + /* Start file offset of the range we want to NOCOW. */ + u64 start; + /* End file offset (inclusive) of the range we want to NOCOW. */ + u64 end; + bool writeback_path; + bool strict; + /* + * Free the path passed to can_nocow_file_extent() once it's not needed + * anymore. + */ + bool free_path; + + /* Output fields. Only set when can_nocow_file_extent() returns 1. */ + + u64 disk_bytenr; + u64 disk_num_bytes; + u64 extent_offset; + /* Number of bytes that can be written to in NOCOW mode. */ + u64 num_bytes; +}; + +/* + * Check if we can NOCOW the file extent that the path points to. + * This function may return with the path released, so the caller should check + * if path->nodes[0] is NULL or not if it needs to use the path afterwards. + * + * Returns: < 0 on error + * 0 if we can not NOCOW + * 1 if we can NOCOW + */ +static int can_nocow_file_extent(struct btrfs_path *path, + struct btrfs_key *key, + struct btrfs_inode *inode, + struct can_nocow_file_extent_args *args) +{ + const bool is_freespace_inode = btrfs_is_free_space_inode(inode); + struct extent_buffer *leaf = path->nodes[0]; + struct btrfs_root *root = inode->root; + struct btrfs_file_extent_item *fi; + u64 extent_end; + u8 extent_type; + int can_nocow = 0; + int ret = 0; + + 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_INLINE) + goto out; + + /* Can't access these fields unless we know it's not an inline extent. */ + args->disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi); + args->disk_num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi); + args->extent_offset = btrfs_file_extent_offset(leaf, fi); + + if (!(inode->flags & BTRFS_INODE_NODATACOW) && + extent_type == BTRFS_FILE_EXTENT_REG) + goto out; + + /* + * If the extent was created before the generation where the last snapshot + * for its subvolume was created, then this implies the extent is shared, + * hence we must COW. + */ + if (!args->strict && !is_freespace_inode && + btrfs_file_extent_generation(leaf, fi) <= + btrfs_root_last_snapshot(&root->root_item)) + goto out; + + /* An explicit hole, must COW. */ + if (args->disk_bytenr == 0) + goto out; + + /* Compressed/encrypted/encoded extents must be COWed. */ + if (btrfs_file_extent_compression(leaf, fi) || + btrfs_file_extent_encryption(leaf, fi) || + btrfs_file_extent_other_encoding(leaf, fi)) + goto out; + + extent_end = btrfs_file_extent_end(path); + + /* + * The following checks can be expensive, as they need to take other + * locks and do btree or rbtree searches, so release the path to avoid + * blocking other tasks for too long. + */ + btrfs_release_path(path); + + ret = btrfs_cross_ref_exist(root, btrfs_ino(inode), + key->offset - args->extent_offset, + args->disk_bytenr, false, path); + WARN_ON_ONCE(ret > 0 && is_freespace_inode); + if (ret != 0) + goto out; + + if (args->free_path) { + /* + * We don't need the path anymore, plus through the + * csum_exist_in_range() call below we will end up allocating + * another path. So free the path to avoid unnecessary extra + * memory usage. + */ + btrfs_free_path(path); + path = NULL; + } + + /* If there are pending snapshots for this root, we must COW. */ + if (args->writeback_path && !is_freespace_inode && + atomic_read(&root->snapshot_force_cow)) + goto out; + + args->disk_bytenr += args->extent_offset; + args->disk_bytenr += args->start - key->offset; + args->num_bytes = min(args->end + 1, extent_end) - args->start; + + /* + * Force COW if csums exist in the range. This ensures that csums for a + * given extent are either valid or do not exist. + */ + ret = csum_exist_in_range(root->fs_info, args->disk_bytenr, args->num_bytes); + WARN_ON_ONCE(ret > 0 && is_freespace_inode); + if (ret != 0) + goto out; + + can_nocow = 1; + out: + if (args->free_path && path) + btrfs_free_path(path); + + return ret < 0 ? ret : can_nocow; +} + /* * when nowcow writeback call back. This checks for snapshots or COW copies * of the extents that exist in the file, and COWs the file as required. @@ -1637,11 +1772,9 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode, u64 cur_offset = start; int ret; bool check_prev = true; - const bool freespace_inode = btrfs_is_free_space_inode(inode); u64 ino = btrfs_ino(inode); bool nocow = false; - u64 disk_bytenr = 0; - const bool force = inode->flags & BTRFS_INODE_NODATACOW; + struct can_nocow_file_extent_args nocow_args = { 0 }; path = btrfs_alloc_path(); if (!path) { @@ -1654,15 +1787,16 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode, return -ENOMEM; } + nocow_args.end = end; + nocow_args.writeback_path = true; + while (1) { struct btrfs_key found_key; struct btrfs_file_extent_item *fi; struct extent_buffer *leaf; u64 extent_end; - u64 extent_offset; - u64 num_bytes = 0; - u64 disk_num_bytes; u64 ram_bytes; + u64 nocow_end; int extent_type; nocow = false; @@ -1738,117 +1872,37 @@ next_slot: fi = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item); extent_type = btrfs_file_extent_type(leaf, fi); - + /* If this is triggered then we have a memory corruption. */ + ASSERT(extent_type < BTRFS_NR_FILE_EXTENT_TYPES); + if (WARN_ON(extent_type >= BTRFS_NR_FILE_EXTENT_TYPES)) { + ret = -EUCLEAN; + goto error; + } ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi); - if (extent_type == BTRFS_FILE_EXTENT_REG || - extent_type == BTRFS_FILE_EXTENT_PREALLOC) { - disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi); - extent_offset = btrfs_file_extent_offset(leaf, fi); - extent_end = found_key.offset + - btrfs_file_extent_num_bytes(leaf, fi); - disk_num_bytes = - btrfs_file_extent_disk_num_bytes(leaf, fi); - /* - * If the extent we got ends before our current offset, - * skip to the next extent. - */ - if (extent_end <= cur_offset) { - path->slots[0]++; - goto next_slot; - } - /* Skip holes */ - if (disk_bytenr == 0) - goto out_check; - /* Skip compressed/encrypted/encoded extents */ - if (btrfs_file_extent_compression(leaf, fi) || - btrfs_file_extent_encryption(leaf, fi) || - btrfs_file_extent_other_encoding(leaf, fi)) - goto out_check; - /* - * If extent is created before the last volume's snapshot - * this implies the extent is shared, hence we can't do - * nocow. This is the same check as in - * btrfs_cross_ref_exist but without calling - * btrfs_search_slot. - */ - if (!freespace_inode && - btrfs_file_extent_generation(leaf, fi) <= - btrfs_root_last_snapshot(&root->root_item)) - goto out_check; - if (extent_type == BTRFS_FILE_EXTENT_REG && !force) - goto out_check; + extent_end = btrfs_file_extent_end(path); - /* - * The following checks can be expensive, as they need to - * take other locks and do btree or rbtree searches, so - * release the path to avoid blocking other tasks for too - * long. - */ - btrfs_release_path(path); + /* + * If the extent we got ends before our current offset, skip to + * the next extent. + */ + if (extent_end <= cur_offset) { + path->slots[0]++; + goto next_slot; + } - ret = btrfs_cross_ref_exist(root, ino, - found_key.offset - - extent_offset, disk_bytenr, - false, path); - if (ret) { - /* - * ret could be -EIO if the above fails to read - * metadata. - */ - if (ret < 0) { - if (cow_start != (u64)-1) - cur_offset = cow_start; - goto error; - } + nocow_args.start = cur_offset; + ret = can_nocow_file_extent(path, &found_key, inode, &nocow_args); + if (ret < 0) { + if (cow_start != (u64)-1) + cur_offset = cow_start; + goto error; + } else if (ret == 0) { + goto out_check; + } - WARN_ON_ONCE(freespace_inode); - goto out_check; - } - disk_bytenr += extent_offset; - disk_bytenr += cur_offset - found_key.offset; - num_bytes = min(end + 1, extent_end) - cur_offset; - /* - * If there are pending snapshots for this root, we - * fall into common COW way - */ - if (!freespace_inode && atomic_read(&root->snapshot_force_cow)) - goto out_check; - /* - * force cow if csum exists in the range. - * this ensure that csum for a given extent are - * either valid or do not exist. - */ - ret = csum_exist_in_range(fs_info, disk_bytenr, - num_bytes); - if (ret) { - /* - * ret could be -EIO if the above fails to read - * metadata. - */ - if (ret < 0) { - if (cow_start != (u64)-1) - cur_offset = cow_start; - goto error; - } - WARN_ON_ONCE(freespace_inode); - goto out_check; - } - /* If the extent's block group is RO, we must COW */ - if (!btrfs_inc_nocow_writers(fs_info, disk_bytenr)) - goto out_check; + ret = 0; + if (btrfs_inc_nocow_writers(fs_info, nocow_args.disk_bytenr)) nocow = true; - } else if (extent_type == BTRFS_FILE_EXTENT_INLINE) { - extent_end = found_key.offset + ram_bytes; - extent_end = ALIGN(extent_end, fs_info->sectorsize); - /* Skip extents outside of our requested range */ - if (extent_end <= start) { - path->slots[0]++; - goto next_slot; - } - } else { - /* If this triggers then we have a memory corruption */ - BUG(); - } out_check: /* * If nocow is false then record the beginning of the range @@ -1880,15 +1934,17 @@ out_check: cow_start = (u64)-1; } + nocow_end = cur_offset + nocow_args.num_bytes - 1; + if (extent_type == BTRFS_FILE_EXTENT_PREALLOC) { - u64 orig_start = found_key.offset - extent_offset; + u64 orig_start = found_key.offset - nocow_args.extent_offset; struct extent_map *em; - em = create_io_em(inode, cur_offset, num_bytes, + em = create_io_em(inode, cur_offset, nocow_args.num_bytes, orig_start, - disk_bytenr, /* block_start */ - num_bytes, /* block_len */ - disk_num_bytes, /* orig_block_len */ + nocow_args.disk_bytenr, /* block_start */ + nocow_args.num_bytes, /* block_len */ + nocow_args.disk_num_bytes, /* orig_block_len */ ram_bytes, BTRFS_COMPRESS_NONE, BTRFS_ORDERED_PREALLOC); if (IS_ERR(em)) { @@ -1897,20 +1953,23 @@ out_check: } free_extent_map(em); ret = btrfs_add_ordered_extent(inode, - cur_offset, num_bytes, num_bytes, - disk_bytenr, num_bytes, 0, + cur_offset, nocow_args.num_bytes, + nocow_args.num_bytes, + nocow_args.disk_bytenr, + nocow_args.num_bytes, 0, 1 << BTRFS_ORDERED_PREALLOC, BTRFS_COMPRESS_NONE); if (ret) { btrfs_drop_extent_cache(inode, cur_offset, - cur_offset + num_bytes - 1, - 0); + nocow_end, 0); goto error; } } else { ret = btrfs_add_ordered_extent(inode, cur_offset, - num_bytes, num_bytes, - disk_bytenr, num_bytes, + nocow_args.num_bytes, + nocow_args.num_bytes, + nocow_args.disk_bytenr, + nocow_args.num_bytes, 0, 1 << BTRFS_ORDERED_NOCOW, BTRFS_COMPRESS_NONE); @@ -1919,7 +1978,7 @@ out_check: } if (nocow) - btrfs_dec_nocow_writers(fs_info, disk_bytenr); + btrfs_dec_nocow_writers(fs_info, nocow_args.disk_bytenr); nocow = false; if (btrfs_is_data_reloc_root(root)) @@ -1929,10 +1988,9 @@ out_check: * from freeing metadata of created ordered extent. */ ret = btrfs_reloc_clone_csums(inode, cur_offset, - num_bytes); + nocow_args.num_bytes); - extent_clear_unlock_delalloc(inode, cur_offset, - cur_offset + num_bytes - 1, + extent_clear_unlock_delalloc(inode, cur_offset, nocow_end, locked_page, EXTENT_LOCKED | EXTENT_DELALLOC | EXTENT_CLEAR_DATA_RESV, @@ -1965,7 +2023,7 @@ out_check: error: if (nocow) - btrfs_dec_nocow_writers(fs_info, disk_bytenr); + btrfs_dec_nocow_writers(fs_info, nocow_args.disk_bytenr); if (ret && cur_offset < end) extent_clear_unlock_delalloc(inode, cur_offset, end, @@ -7107,6 +7165,7 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len, u64 *ram_bytes, bool strict) { struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); + struct can_nocow_file_extent_args nocow_args = { 0 }; struct btrfs_path *path; int ret; struct extent_buffer *leaf; @@ -7114,13 +7173,7 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len, struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree; struct btrfs_file_extent_item *fi; struct btrfs_key key; - u64 disk_bytenr; - u64 backref_offset; - u64 extent_end; - u64 num_bytes; - int slot; int found_type; - bool nocow = (BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW); path = btrfs_alloc_path(); if (!path) @@ -7131,18 +7184,17 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len, if (ret < 0) goto out; - slot = path->slots[0]; if (ret == 1) { - if (slot == 0) { + if (path->slots[0] == 0) { /* can't find the item, must cow */ ret = 0; goto out; } - slot--; + path->slots[0]--; } ret = 0; leaf = path->nodes[0]; - btrfs_item_key_to_cpu(leaf, &key, slot); + btrfs_item_key_to_cpu(leaf, &key, path->slots[0]); if (key.objectid != btrfs_ino(BTRFS_I(inode)) || key.type != BTRFS_EXTENT_DATA_KEY) { /* not our file or wrong item type, must cow */ @@ -7154,57 +7206,38 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len, goto out; } - fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item); - found_type = btrfs_file_extent_type(leaf, fi); - if (found_type != BTRFS_FILE_EXTENT_REG && - found_type != BTRFS_FILE_EXTENT_PREALLOC) { - /* not a regular extent, must cow */ - goto out; - } - - if (!nocow && found_type == BTRFS_FILE_EXTENT_REG) + if (btrfs_file_extent_end(path) <= offset) goto out; - extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi); - if (extent_end <= offset) - goto out; + fi = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item); + found_type = btrfs_file_extent_type(leaf, fi); + if (ram_bytes) + *ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi); - disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi); - if (disk_bytenr == 0) - goto out; + nocow_args.start = offset; + nocow_args.end = offset + *len - 1; + nocow_args.strict = strict; + nocow_args.free_path = true; - if (btrfs_file_extent_compression(leaf, fi) || - btrfs_file_extent_encryption(leaf, fi) || - btrfs_file_extent_other_encoding(leaf, fi)) - goto out; + ret = can_nocow_file_extent(path, &key, BTRFS_I(inode), &nocow_args); + /* can_nocow_file_extent() has freed the path. */ + path = NULL; - /* - * Do the same check as in btrfs_cross_ref_exist but without the - * unnecessary search. - */ - if (!strict && - (btrfs_file_extent_generation(leaf, fi) <= - btrfs_root_last_snapshot(&root->root_item))) + if (ret != 1) { + /* Treat errors as not being able to NOCOW. */ + ret = 0; goto out; - - backref_offset = btrfs_file_extent_offset(leaf, fi); - - if (orig_start) { - *orig_start = key.offset - backref_offset; - *orig_block_len = btrfs_file_extent_disk_num_bytes(leaf, fi); - *ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi); } - btrfs_release_path(path); - - if (btrfs_extent_readonly(fs_info, disk_bytenr)) + ret = 0; + if (btrfs_extent_readonly(fs_info, nocow_args.disk_bytenr)) goto out; - num_bytes = min(offset + *len, extent_end) - offset; - if (!nocow && found_type == BTRFS_FILE_EXTENT_PREALLOC) { + if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW) && + found_type == BTRFS_FILE_EXTENT_PREALLOC) { u64 range_end; - range_end = round_up(offset + num_bytes, + range_end = round_up(offset + nocow_args.num_bytes, root->fs_info->sectorsize) - 1; ret = test_range_bit(io_tree, offset, range_end, EXTENT_DELALLOC, 0, NULL); @@ -7214,42 +7247,12 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len, } } - /* - * look for other files referencing this extent, if we - * find any we must cow - */ + if (orig_start) + *orig_start = key.offset - nocow_args.extent_offset; + if (orig_block_len) + *orig_block_len = nocow_args.disk_num_bytes; - ret = btrfs_cross_ref_exist(root, btrfs_ino(BTRFS_I(inode)), - key.offset - backref_offset, disk_bytenr, - strict, path); - if (ret) { - ret = 0; - goto out; - } - - /* - * We don't need the path anymore, plus through the csum_exist_in_range() - * call below we will end up allocating another path. So free the path - * to avoid unnecessary extra memory usage. - */ - btrfs_free_path(path); - path = NULL; - - /* - * adjust disk_bytenr and num_bytes to cover just the bytes - * in this extent we are about to write. If there - * are any csums in that range we have to cow in order - * to keep the csums correct - */ - disk_bytenr += backref_offset; - disk_bytenr += offset - key.offset; - if (csum_exist_in_range(fs_info, disk_bytenr, num_bytes)) - goto out; - /* - * all of the above have passed, it is safe to overwrite this extent - * without cow - */ - *len = num_bytes; + *len = nocow_args.num_bytes; ret = 1; out: btrfs_free_path(path); -- 2.7.4