Re: [PATCH 2/6] common: capture metadump output if xfs filesystem check fails

From: Brian Foster <bfoster@redhat.com>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: guaneryu@gmail.com, linux-xfs@vger.kernel.org,
	fstests@vger.kernel.org, guan@eryu.me
Subject: Re: [PATCH 2/6] common: capture metadump output if xfs filesystem check fails
Date: Thu, 11 Feb 2021 08:59:58 -0500	[thread overview]
Message-ID: <20210211135958.GB222065@bfoster> (raw)
In-Reply-To: <161292579087.3504537.10519481439481869013.stgit@magnolia>

On Tue, Feb 09, 2021 at 06:56:30PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@djwong.org>
> 
> Capture metadump output when various userspace repair and checker tools
> fail or indicate corruption, to aid in debugging.  We don't bother to
> annotate xfs_check because it's bitrotting.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  README     |    2 ++
>  common/xfs |   26 ++++++++++++++++++++++++++
>  2 files changed, 28 insertions(+)
> 
> 
> diff --git a/README b/README
> index 43bb0cee..36f72088 100644
> --- a/README
> +++ b/README
> @@ -109,6 +109,8 @@ Preparing system for tests:
>               - Set TEST_FS_MODULE_RELOAD=1 to unload the module and reload
>                 it between test invocations.  This assumes that the name of
>                 the module is the same as FSTYP.
> +	     - Set SNAPSHOT_CORRUPT_XFS=1 to record compressed metadumps of XFS
> +	       filesystems if the various stages of _check_xfs_filesystem fail.
>  
>          - or add a case to the switch in common/config assigning
>            these variables based on the hostname of your test
> diff --git a/common/xfs b/common/xfs
> index 2156749d..ad1eb6ee 100644
> --- a/common/xfs
> +++ b/common/xfs
> @@ -432,6 +432,21 @@ _supports_xfs_scrub()
>  	return 0
>  }
>  
> +# Save a compressed snapshot of a corrupt xfs filesystem for later debugging.
> +_snapshot_xfs() {

The term snapshot has a well known meaning. Can we just call this
_metadump_xfs()?

> +	local metadump="$1"
> +	local device="$2"
> +	local logdev="$3"
> +	local options="-a -o"
> +
> +	if [ "$logdev" != "none" ]; then
> +		options="$options -l $logdev"
> +	fi
> +
> +	$XFS_METADUMP_PROG $options "$device" "$metadump" >> "$seqres.full" 2>&1
> +	gzip -f "$metadump" >> "$seqres.full" 2>&1 &

Why compress in the background? I wonder if we should just skip the
compression step since this requires an option to enable in the first
place..

> +}
> +
>  # run xfs_check and friends on a FS.
>  _check_xfs_filesystem()
>  {
...
> @@ -540,6 +564,8 @@ _check_xfs_filesystem()
>  			cat $tmp.repair				>>$seqres.full
>  			echo "*** end xfs_repair output"	>>$seqres.full
>  
> +			test "$SNAPSHOT_CORRUPT_XFS" = "1" && \
> +				_snapshot_xfs "$seqres.rebuildrepair.md" "$device" "$2"

Why do we collect so many metadump images? Shouldn't all but the last
TEST_XFS_REPAIR_REBUILD thing not modify the fs? If so, it seems like we
should be able to collect one image (and perhaps just call it
"$seqres.$device.md") if any of the first several checks flag a problem.

Brian

>  			ok=0
>  		fi
>  		rm -f $tmp.repair
> 