From: Dominique Martinet <dominique.marti...@atmark-techno.com>
btrfs_read_extent_reg correctly computed the extent offset in the
BTRFS_COMPRESS_NONE case, but did not account for the 'offset - key.offset'
part correctly in the compressed case, making the function read
incorrect data.
In the case I examined, the last 4k of a file was corrupted and
contained data from a few blocks prior, e.g. reading a 10k file with a
single extent:
btrfs_file_read()
-> btrfs_read_extent_reg
(aligned part loop, until 8k)
-> read_and_truncate_page
-> btrfs_read_extent_reg
(re-reads the last extent from 8k to the end,
incorrectly reading the first 2k of data)
This can be reproduced as follow:
$ truncate -s 200M btr
$ mount btr -o compress /mnt
$ pat() { dd if=/dev/zero bs=1M count=$1 iflag=count_bytes status=none | tr
'\0' "\\$2"; }
$ { pat 4K 1; pat 4K 2; pat 2K 3; } > /mnt/file
$ sync
$ filefrag -v /mnt/file
File size of /mnt/file is 10240 (3 blocks of 4096 bytes)
ext: logical_offset: physical_offset: length: expected: flags:
0: 0.. 2: 3328.. 3330: 3:
last,encoded,eof
$ umount /mnt
Then in u-boot:
=> load scsi 0 2000000 file
10240 bytes read in 3 ms (3.3 MiB/s)
=> md 2001ff0
02001ff0: 02020202 02020202 02020202 02020202 ................
02002000: 01010101 01010101 01010101 01010101 ................
02002010: 01010101 01010101 01010101 01010101 ................
(02002000 onwards should contain '03' pattern but went back to 01,
start of the extent)
After patch, data is read properly:
=> md 2001ff0
02001ff0: 02020202 02020202 02020202 02020202 ................
02002000: 03030303 03030303 03030303 03030303 ................
02002010: 03030303 03030303 03030303 03030303 ................
Note that the code previously (before commit e3427184f38a ("fs: btrfs:
Implement btrfs_file_read()")) did not split that read in two, so
this is a regression even if the previous code might not have been
handling offsets correctly either (something that booted now fails to
boot)
Fixes: a26a6bedafcf ("fs: btrfs: Introduce btrfs_read_extent_inline() and
btrfs_read_extent_reg()")
Signed-off-by: Dominique Martinet <dominique.marti...@atmark-techno.com>
---
Changes in v2:
- Keep offset decomposition explicit where it is used
- Add reproducer/clarify explanation in commit message
- Drop other patches temporarily
- Link to v1:
https://lore.kernel.org/r/20230418-btrfs-extent-reads-v1-0-47ba9839f...@codewreck.org
---
fs/btrfs/inode.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 40025662f250..38e285bf94b0 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -511,7 +511,9 @@ int btrfs_read_extent_reg(struct btrfs_path *path,
if (ret < dsize)
memset(dbuf + ret, 0, dsize - ret);
/* Then copy the needed part */
- memcpy(dest, dbuf + btrfs_file_extent_offset(leaf, fi), len);
+ memcpy(dest,
+ dbuf + btrfs_file_extent_offset(leaf, fi) + offset - key.offset,
+ len);
ret = len;
out:
free(cbuf);
---
base-commit: 5db4972a5bbdbf9e3af48ffc9bc4fec73b7b6a79
change-id: 20230418-btrfs-extent-reads-e2df6e329ad4
Best regards,
--
Dominique Martinet | Asmadeus
