On Mon, Dec 27, 2021 at 02:11:14PM +0800, Qu Wenruo wrote:
[BUG] When passing a btrfs with NO_HOLE feature to U-boot, and if one file contains holes, then the hash of the file is not correct in U-boot:
# mkfs.btrfs -f test.img # Since v5.15, mkfs defaults to NO_HOLES # mount test.img /mnt/btrfs # xfs_io -f -c "pwrite 0 4k" -c "pwrite 8k 4k" /mnt/btrfs/file # md5sum /mnt/btrfs/file 277f3840b275c74d01e979ea9d75ac19 /mnt/btrfs/file # umount /mnt/btrfs # ./u-boot => host bind 0 /home/adam/test.img => ls host 0 < > 12288 Mon Dec 27 05:35:23 2021 file => load host 0 0x1000000 file 12288 bytes read in 0 ms => md5sum 0x1000000 0x3000 md5 for 01000000 ... 01002fff ==> 855ffdbe4d0ccc5acab92e1b5330e4c1
The md5sum doesn't match at all.
[CAUSE] In U-boot btrfs implementation, the function btrfs_read_file() has the following iteration for file extent iteration:
/* Read the aligned part */ while (cur < aligned_end) { ret = lookup_data_extent(root, &path, ino, cur, &next_offset); if (ret < 0) goto out; if (ret > 0) { /* No next, direct exit */ if (!next_offset) { ret = 0; goto out; } } /* Read file extent */
But for NO_HOLES features, hole extents will not have any extent item for it. Thus if @cur is at a hole, lookup_data_extent() will just return >0, and update @next_offset.
But we still believe there is some data to read for @cur for ret > 0 case, causing we read extent data from the next file extent.
This means, what we do for above NO_HOLES btrfs is:
Read 4K data from disk to file offset [0, 4K) So far the data is still correct
Read 4K data from disk to file offset [4K, 8K) We didn't skip the 4K hole, but read the data at file offset [8K, 12K) into file offset [4K, 8K).
This causes the checksum mismatch.
[FIX] Add extra check to skip to the next non-hole range after lookup_data_extent().
Signed-off-by: Qu Wenruo wqu@suse.com
Applied to u-boot/master, thanks!