On 2021/12/27 14:11, 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

This bug exposed another missing link, that we don't have good test coverage in U-boot btrfs.

This is partially caused by the fact that, btrfs-progs code is not designed to read file contents, but just to check the cross-reference (aka, btrfs-check).

If we really only want read-only support in U-boot, and don't ever plan to add write support, then I'd say the btrfs-fuse project (https://github.com/adam900710/btrfs-fuse/) is more suitable for U-boot.

As that project already has full fs content verification selftest along with extra multi-device recovery tests. And shares the same code style between btrfs-progs/kernel.

OK, things are not that bad.

In fact, the btrfs_read_file() implementation in btrfs-fuse has the same naming, same lookup_file_extent() (just a little naming different than lookup_data_extent()), same parameter list.

Just without the unaligned sector handling (handled by FUSE, and it may also be unnecessary for U-boot too), and already have the correct handling for lookup_file_extent(), thanks to the selftest.

So this already means, it can be pretty easy for U-boot to take code from btrfs-fuse part by part, without huge refactor again.

Thanks, Qu

---

fs/btrfs/inode.c | 8 ++++++++ 1 file changed, 8 insertions(+)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 2c2379303d74..d00b5153336d 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -717,6 +717,14 @@ int btrfs_file_read(struct btrfs_root *root, u64 ino, u64 file_offset, u64 len, ret = 0; goto out; }

• 	/*
  

• 	 * Find a extent gap, mostly caused by NO_HOLE feature.
  

• 	 * Just to next offset directly.
  

• 	 */
  

• 	if (next_offset > cur) {
  

• 		cur = next_offset;
  

• 		continue;
  

• 	}
  

  } fi = btrfs_item_ptr(path.nodes[0], path.slots[0], struct btrfs_file_extent_item);