Re: [PATCH 1/9] btrfs: add a helpers for read repair testing

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2022/5/24 15:18, Christoph Hellwig wrote:
> Add a few helpers to consolidate code for btrfs read repair testing:
>
>   - _btrfs_get_first_logical() gets the btrfs logical address for the
>     first extent in a file
>   - _btrfs_get_device_path and _btrfs_get_physical use the
>     btrfs-map-logical tool to find the device path and physical address
>     for btrfs logical address for a specific mirror
>   - _btrfs_direct_read_on_mirror and _btrfs_buffered_read_on_mirror
>     read the data from a specific mirror
>
> These will be used to consolidate the read repair tests and avoid
> duplication for new tests.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Qu Wenruo <wqu@suse.com>

Some some small nitpicks inlined below.
> ---
>   common/btrfs  | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++
>   common/config |  1 +
>   2 files changed, 76 insertions(+)
>
> diff --git a/common/btrfs b/common/btrfs
> index ac597ca4..129a83f7 100644
> --- a/common/btrfs
> +++ b/common/btrfs
> @@ -505,3 +505,78 @@ _btrfs_metadump()
>   	$BTRFS_IMAGE_PROG "$device" "$dumpfile"
>   	[ -n "$DUMP_COMPRESSOR" ] && $DUMP_COMPRESSOR -f "$dumpfile" &> /dev/null
>   }
> +
> +# Return the btrfs logical address for the first block in a file
> +_btrfs_get_first_logical()
> +{
> +	local file=$1
> +	_require_command "$FILEFRAG_PROG" filefrag
> +
> +	${FILEFRAG_PROG} -v $SCRATCH_MNT/foobar >> $seqres.full
> +	${FILEFRAG_PROG} -v $file | _filter_filefrag | cut -d '#' -f 1
> +}
> +
> +# Find the device path for a btrfs logical offset
> +_btrfs_get_device_path()
> +{
> +	local logical=$1
> +	local stripe=$2
> +
> +	_require_command "$BTRFS_MAP_LOGICAL_PROG" btrfs-map-logical
> +
> +	$BTRFS_MAP_LOGICAL_PROG -l $logical $SCRATCH_DEV | \
> +		$AWK_PROG "(\$1 ~ /mirror/ && \$2 ~ /$stripe/) { print \$8 }"
> +}
> +
> +
> +# Find the device physical sector for a btrfs logical offset
> +_btrfs_get_physical()
> +{
> +	local logical=$1
> +	local stripe=$2
> +
> +	_require_command "$BTRFS_MAP_LOGICAL_PROG" btrfs-map-logical
> +
> +	$BTRFS_MAP_LOGICAL_PROG -l $logical $SCRATCH_DEV >> $seqres.full 2>&1
> +	$BTRFS_MAP_LOGICAL_PROG -l $logical $SCRATCH_DEV | \
> +		$AWK_PROG "(\$1 ~ /mirror/ && \$2 ~ /$stripe/) { print \$6 }"

Since the map logical output is saved into seqres, maybe it's better to
add "-b <sectorsize>" parameters.

The default bytes is the nodesize (which is super werid), thus under
corner cases, like at the stripe boundary, it can return multiple result
groups and cause some confusion.

Although we will need another helper to grab the sectorsize of a mounted
btrfs though.

Thanks,
Qu
> +}
> +
> +# Read from a specific stripe to test read recovery that corrupted a specific
> +# stripe.  Btrfs uses the PID to select the mirror, so keep reading until the
> +# xfs_io process that performed the read was executed with a PID that ends up
> +# on the intended mirror.
> +_btrfs_direct_read_on_mirror()
> +{
> +	local mirror=$1
> +	local nr_mirrors=$2
> +	local file=$3
> +	local offset=$4
> +	local size=$5
> +
> +	while [[ -z $( (( BASHPID % nr_mirrors == mirror )) &&
> +		exec $XFS_IO_PROG -d \
> +			-c "pread -b $size $offset $size" $file) ]]; do
> +		:
> +	done
> +}
> +
> +# Read from a specific stripe to test read recovery that corrupted a specific
> +# stripe.  Btrfs uses the PID to select the mirror, so keep reading until the
> +# xfs_io process that performed the read was executed with a PID that ends up
> +# on the intended mirror.
> +_btrfs_buffered_read_on_mirror()
> +{
> +	local mirror=$1
> +	local nr_mirrors=$2
> +	local file=$3
> +	local offset=$4
> +	local size=$5
> +
> +	echo 3 > /proc/sys/vm/drop_caches
> +	while [[ -z $( (( BASHPID % nr_mirrors == mirror )) &&
> +		exec $XFS_IO_PROG \
> +			-c "pread -b $size $offset $size" $file) ]]; do
> +		:
> +	done
> +}
> diff --git a/common/config b/common/config
> index c6428f90..df20afc1 100644
> --- a/common/config
> +++ b/common/config
> @@ -228,6 +228,7 @@ export E2IMAGE_PROG="$(type -P e2image)"
>   export BLKZONE_PROG="$(type -P blkzone)"
>   export GZIP_PROG="$(type -P gzip)"
>   export BTRFS_IMAGE_PROG="$(type -P btrfs-image)"
> +export BTRFS_MAP_LOGICAL_PROG=$(type -P btrfs-map-logical)
>
>   # use 'udevadm settle' or 'udevsettle' to wait for lv to be settled.
>   # newer systems have udevadm command but older systems like RHEL5 don't.