[PATCH v3 2/3] generic/574: corrupt btrfs merkle tree data

[Boris Burkov <boris@bur.io>]

generic/574 has tests for corrupting the merkle tree data stored by the
filesystem. Since btrfs uses a different scheme for storing this data,
the existing logic for corrupting it doesn't work out of the box. Adapt
it to properly corrupt btrfs merkle items.

Note that there is a bit of a kludge here: since btrfs_corrupt_block
doesn't handle streaming corruption bytes from stdin (I could change
that, but it feels like overkill for this purpose), I just read the
first corruption byte and duplicate it for the desired length. That is
how the test is using the interface in practice, anyway.

This relies on the following kernel patch for btrfs verity support:
<btrfs-verity-patch>
And the following btrfs-progs patch for btrfs_corrupt_block support:
<btrfs-corrupt-block-patch>

Signed-off-by: Boris Burkov <boris@bur.io>
---
 common/verity | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/common/verity b/common/verity
index d2c1ea24..fdd05783 100644
--- a/common/verity
+++ b/common/verity
@@ -3,8 +3,7 @@
 #
 # Functions for setting up and testing fs-verity
 
-_require_scratch_verity()
-{
+_require_scratch_verity() {
 	_require_scratch
 	_require_command "$FSVERITY_PROG" fsverity
 
@@ -315,6 +314,18 @@ _fsv_scratch_corrupt_merkle_tree()
 		(( offset += ($(_get_filesize $file) + 65535) & ~65535 ))
 		_fsv_scratch_corrupt_bytes $file $offset
 		;;
+	btrfs)
+		ino=$(ls -i $file | awk '{print $1}')
+		sync
+		cat > $tmp.bytes
+		sz=$(_get_filesize $tmp.bytes)
+		read -n 1 byte < $tmp.bytes
+		ascii=$(printf "%d" "'$byte'")
+		_scratch_unmount
+		$BTRFS_CORRUPT_BLOCK_PROG -r 5 -I $ino,37,0 -v $ascii -o $offset -b $sz $SCRATCH_DEV
+		sync
+		_scratch_mount
+		;;
 	*)
 		_fail "_fsv_scratch_corrupt_merkle_tree() unimplemented on $FSTYP"
 		;;
-- 
2.30.2