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

[Eryu Guan <guan@eryu.me>]

On Thu, Apr 08, 2021 at 11:57:50AM -0700, Boris Burkov wrote:
> 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() {

No need to change this.

>  	_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}')

stat -c %i $1

And declare local variables with local.

> +		sync

Why a system wide sync is needed here?

> +		cat > $tmp.bytes

I think this cat would just hang there.

> +		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

It'd be better to explain this command in comments.

> +		sync

Again, is this sync really needed?

Thanks,
Eryu

> +		_scratch_mount
> +		;;
>  	*)
>  		_fail "_fsv_scratch_corrupt_merkle_tree() unimplemented on $FSTYP"
>  		;;
> -- 
> 2.30.2