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>
---
lib/ext2fs/ext2fs.h | 3 ++-
lib/ext2fs/fallocate.c | 21 +++++++++++++++++++--
2 files changed, 21 insertions(+), 3 deletions(-)
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.
--
2.47.0.rc1.288.g06298d1525-goog
