On Thu, Dec 19, 2024 at 07:46:13PM -0800, Sarthak Kukreti wrote: > 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 Looks good Sarthak, feel free to add: Reviewed-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx> Regards, ojaswin > > --- > 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 >
