Re: [PATCH v5 1/8] common/rc: Introduce new helpers for DAX mount options and FS_XFLAG_DAX

[Xiao Yang <yangx.jy@cn.fujitsu.com>]

On 2020/7/9 17:49, Xiao Yang wrote:
> 1) _require_scratch_dax_mountopt() checks both old and new DAX mount option
> 2) _require_dax_iflag() checks FS_XFLAG_DAX
>
> Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
> ---
>
> V4->V5:
> 1) Rename _require_scratch_dax_iflag to _require_dax_iflag
> 2) Redirect the output of _try_scratch_mount to /dev/null
>
>  common/rc | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
>
> diff --git a/common/rc b/common/rc
> index f17b19f2..498ce230 100644
> --- a/common/rc
> +++ b/common/rc
> @@ -3188,6 +3188,41 @@ _require_scratch_dax()
>  	_scratch_unmount
>  }
>  
> +_require_scratch_dax_mountopt()
> +{
> +	local mountopt=$1
> +	local output
> +
> +	_require_scratch
> +	_scratch_mkfs > /dev/null 2>&1
> +	_try_scratch_mount "-o $mountopt" > /dev/null 2>&1 || \
> +		_notrun "mount $SCRATCH_DEV with $mountopt failed"
> +
> +	output=$(_fs_options $SCRATCH_DEV)
> +
> +	# For new dax mount option, /proc/mounts shows different outputs if we
> +	# mount with -o dax=inode on ext4 and xfs so skip checking it.
> +	# /proc/mounts shows 'dax=inode' on ext4 but shows nothing on xfs.
> +	if [ "$mountopt" != "dax=inode" ]; then
> +		echo $output | grep -qw "$mountopt" || \
> +			_notrun "$SCRATCH_DEV $FSTYP does not support -o $mountopt"
> +	fi
> +
> +	# For new dax mount option, /proc/mounts shows "dax=never" if we
> +	# mount with -o dax on xfs and underlying device doesn't support dax.
> +	if [ "$mountopt" = "dax" ]; then
> +		echo $output | grep -qw "dax=never" && \
> +			_notrun "$SCRATCH_DEV $FSTYP does not support -o $mountopt"
> +	fi
> +
> +	_scratch_unmount
> +}
Hi Darrick, Ira

I wonder if we just need to check two dax options(i.e. old 'dax' option
and new 'dax=always' option)
because of the following reasons:
1) we cannot detect if underlying device supports dax by mounting
dax=inode or dax=never.
2) dax=always, dax=inode, dax=never are always introduced together on
all distros.

Best Regards,
Xiao Yang
> +
> +_require_dax_iflag()
> +{
> +	_require_xfs_io_command "chattr" "x"
> +}
> +
>  # Does norecovery support by this fs?
>  _require_norecovery()
>  {