Add a new flag to add support for fixed goal allocations in ext_falloc_helper. For fixed goal allocations, omit merging extents and return an error unless the exact extent is found. Use case: On ChromiumOS, we'd like to add the capability of resetting a filesystem while preserving a set of files in-place. This will be used during filesystem reset flows where everything apart from select files (which contain system applications) should be removed: the combined size of the files can exceed the amount of available space in other partitions/memory. The reset process will look something like: 1. Reset code dumps the FIEMAP of the set of preserved files into a file. 2. Mkfs.ext4 is called on the filesystem with -E nodiscard. 3. Post mkfs, the reset code will utilize ext2fs_fallocate w/ EXT2_FALLOCATE_FIXED_GOAL | EXT2_FALLOCATE_FORCE_INIT on the extent list created in step 1. Signed-off-by: Sarthak Kukreti <sarthakkukreti@xxxxxxxxxx> Changes from v1 (https://lists.openwall.net/linux-ext4/2024/12/12/38): - s/EXT2_NEWRANGE_EXACT_GOAL/EXT2_NEWRANGE_FIXED_GOAL --- lib/ext2fs/alloc.c | 2 +- lib/ext2fs/ext2fs.h | 3 ++- lib/ext2fs/fallocate.c | 21 +++++++++++++++++++-- 3 files changed, 22 insertions(+), 4 deletions(-) diff --git a/lib/ext2fs/alloc.c b/lib/ext2fs/alloc.c index 3fd92167..ba5b1c5e 100644 --- a/lib/ext2fs/alloc.c +++ b/lib/ext2fs/alloc.c @@ -390,7 +390,7 @@ no_blocks: /* * Starting at _goal_, scan around the filesystem to find a run of free blocks * that's at least _len_ blocks long. Possible flags: - * - EXT2_NEWRANGE_EXACT_GOAL: The range of blocks must start at _goal_. + * - EXT2_NEWRANGE_FIXED_GOAL: The range of blocks must start at _goal_. * - EXT2_NEWRANGE_MIN_LENGTH: do not return a allocation shorter than _len_. * - EXT2_NEWRANGE_ZERO_BLOCKS: Zero blocks pblk to pblk+plen before returning. * diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h index 6e87829f..313c5981 100644 --- a/lib/ext2fs/ext2fs.h +++ b/lib/ext2fs/ext2fs.h @@ -1446,7 +1446,8 @@ extern errcode_t ext2fs_decode_extent(struct ext2fs_extent *to, void *from, #define EXT2_FALLOCATE_FORCE_INIT (0x2) #define EXT2_FALLOCATE_FORCE_UNINIT (0x4) #define EXT2_FALLOCATE_INIT_BEYOND_EOF (0x8) -#define EXT2_FALLOCATE_ALL_FLAGS (0xF) +#define EXT2_FALLOCATE_FIXED_GOAL (0x10) +#define EXT2_FALLOCATE_ALL_FLAGS (0x1F) errcode_t ext2fs_fallocate(ext2_filsys fs, int flags, ext2_ino_t ino, struct ext2_inode *inode, blk64_t goal, blk64_t start, blk64_t len); diff --git a/lib/ext2fs/fallocate.c b/lib/ext2fs/fallocate.c index 5cde7d5c..20aa9c9f 100644 --- a/lib/ext2fs/fallocate.c +++ b/lib/ext2fs/fallocate.c @@ -103,7 +103,7 @@ static errcode_t ext_falloc_helper(ext2_filsys fs, blk64_t alloc_goal) { struct ext2fs_extent newex, ex; - int op; + int op, new_range_flags = 0; blk64_t fillable, pblk, plen, x, y; blk64_t eof_blk = 0, cluster_fill = 0; errcode_t err; @@ -132,6 +132,9 @@ static errcode_t ext_falloc_helper(ext2_filsys fs, max_uninit_len = EXT_UNINIT_MAX_LEN & ~EXT2FS_CLUSTER_MASK(fs); max_init_len = EXT_INIT_MAX_LEN & ~EXT2FS_CLUSTER_MASK(fs); + if (flags & EXT2_FALLOCATE_FIXED_GOAL) + goto no_implied; + /* We must lengthen the left extent to the end of the cluster */ if (left_ext && EXT2FS_CLUSTER_RATIO(fs) > 1) { /* How many more blocks can be attached to left_ext? */ @@ -605,12 +608,15 @@ no_implied: max_extent_len = max_uninit_len; newex.e_flags = EXT2_EXTENT_FLAGS_UNINIT; } + + if (flags & EXT2_FALLOCATE_FIXED_GOAL) + new_range_flags = EXT2_NEWRANGE_FIXED_GOAL | EXT2_NEWRANGE_MIN_LENGTH; pblk = alloc_goal; y = range_len; for (x = 0; x < y;) { cluster_fill = newex.e_lblk & EXT2FS_CLUSTER_MASK(fs); fillable = min(range_len + cluster_fill, max_extent_len); - err = ext2fs_new_range(fs, 0, pblk & ~EXT2FS_CLUSTER_MASK(fs), + err = ext2fs_new_range(fs, new_range_flags, pblk & ~EXT2FS_CLUSTER_MASK(fs), fillable, NULL, &pblk, &plen); if (err) @@ -681,6 +687,16 @@ static errcode_t extent_fallocate(ext2_filsys fs, int flags, ext2_ino_t ino, if (err) return err; + /* + * For fixed goal allocations, let the allocations fail iff we can't + * find the exact goal extent. + */ + if (flags & EXT2_FALLOCATE_FIXED_GOAL) { + err = ext_falloc_helper(fs, flags, ino, inode, handle, NULL, + NULL, start, len, goal); + goto errout; + } + /* * Find the extent closest to the start of the alloc range. We don't * check the return value because _goto() sets the current node to the @@ -796,6 +812,7 @@ errout: * - EXT2_FALLOCATE_FORCE_INIT: Create only initialized extents. * - EXT2_FALLOCATE_FORCE_UNINIT: Create only uninitialized extents. * - EXT2_FALLOCATE_INIT_BEYOND_EOF: Create extents beyond EOF. + * - EXT2_FALLOCATE_FIXED_GOAL: Ensure range starts at goal. * * If neither FORCE_INIT nor FORCE_UNINIT are specified, this function will * try to expand any extents it finds, zeroing blocks as necessary. -- 2.47.1.613.gc27f4b7a9f-goog
