Re: [PATCH 01/10] btrfs: add a helpers for read repair testing

[Anand Jain <anand.jain@oracle.com>]

On 5/27/22 13:49, 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>
> ---
>   common/btrfs  | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++
>   common/config |  1 +
>   2 files changed, 76 insertions(+)
> 
> diff --git a/common/btrfs b/common/btrfs
> index ac597ca4..b69feeee 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 -b -l $logical $SCRATCH_DEV >> $seqres.full 2>&1
> +	$BTRFS_MAP_LOGICAL_PROG -l $logical $SCRATCH_DEV | \
> +		$AWK_PROG "(\$1 ~ /mirror/ && \$2 ~ /$stripe/) { print \$6 }"
> +}
> +
> +# 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

I am confused if it should be BASHPID or PID?

Next, it is ok if the xfs_io_prog fails and returns != 0.
(Part of the test).
But then we will continue in the while loop. No?

Sorry, I am sceptical about this. Could you please clarify
how this works?


Thanks, Anand



> +		:
> +	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.