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Subject: Re: [PATCH 02/10] xfs_info: use findmnt to handle mounted block
 devices
References: <155594788997.115924.16224143537288136652.stgit@magnolia>
 <155594790268.115924.87682432738525436.stgit@magnolia>
From: Eric Sandeen <sandeen@sandeen.net>
Message-ID: <f8374061-d7b2-802d-617c-9e38745332ee@sandeen.net>
Date: Mon, 22 Apr 2019 13:35:00 -0500
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To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org

On 4/22/19 10:45 AM, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Use findmnt to determine if the passed-in argument is associated with a
> mount point, and if so, use spaceman to query the mounted filesystem.
> If the user passed in a file, try to find out if it's a loop mounted
> live filesystem and if so query the live filesystem.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

older util-linux doesn't have -O either, but that's getting really old
and I guess we'll burn that bridge if we come to it.

Reviewed-by: Eric Sandeen <sandeen@redhat.com>

> ---
>  debian/control       |    2 +-
>  spaceman/xfs_info.sh |   22 +++++++++++++++++++---
>  2 files changed, 20 insertions(+), 4 deletions(-)
> 
> 
> diff --git a/debian/control b/debian/control
> index f4f807b0..0b3205f5 100644
> --- a/debian/control
> +++ b/debian/control
> @@ -8,7 +8,7 @@ Standards-Version: 4.0.0
>  Homepage: https://xfs.wiki.kernel.org/
>  
>  Package: xfsprogs
> -Depends: ${shlibs:Depends}, ${misc:Depends}, python3:any
> +Depends: ${shlibs:Depends}, ${misc:Depends}, python3:any, util-linux
>  Provides: fsck-backend
>  Suggests: xfsdump, acl, attr, quota
>  Breaks: xfsdump (<< 3.0.0)
> diff --git a/spaceman/xfs_info.sh b/spaceman/xfs_info.sh
> index ecf17f61..1bf6d2c3 100755
> --- a/spaceman/xfs_info.sh
> +++ b/spaceman/xfs_info.sh
> @@ -7,6 +7,14 @@
>  OPTS=""
>  USAGE="Usage: xfs_info [-V] [-t mtab] [mountpoint|device|file]"
>  
> +# Try to find a loop device associated with a file.  We only want to return
> +# one loopdev (multiple loop devices can attach to a single file) so we grab
> +# the last line and return it if it's actually a block device.
> +try_find_loop_dev_for_file() {
> +	local x="$(losetup -O NAME -j "$1" 2> /dev/null | tail -n 1)"
> +	test -b "$x" && echo "$x"
> +}
> +
>  while getopts "t:V" c
>  do
>  	case $c in
> @@ -24,11 +32,19 @@ set -- extra "$@"
>  shift $OPTIND
>  case $# in
>  	1)
> -		if [ -b "$1" ] || [ -f "$1" ]; then
> -			xfs_db -p xfs_info -c "info" $OPTS "$1"
> +		arg="$1"
> +
> +		# See if we can map the arg to a loop device
> +		loopdev="$(try_find_loop_dev_for_file "${arg}")"
> +		test -n "${loopdev}" && arg="${loopdev}"
> +
> +		# If we find a mountpoint for the device, do a live query;
> +		# otherwise try reading the fs with xfs_db.
> +		if mountpt="$(findmnt -f -n -o TARGET "${arg}" 2> /dev/null)"; then
> +			xfs_spaceman -p xfs_info -c "info" $OPTS "${mountpt}"
>  			status=$?
>  		else
> -			xfs_spaceman -p xfs_info -c "info" $OPTS "$1"
> +			xfs_db -p xfs_info -c "info" $OPTS "${arg}"
>  			status=$?
>  		fi
>  		;;
>