Re: [PATCH v6 1/7] common/rc: Introduce new helpers for DAX mount options and FS_XFLAG_DAX

From: Ira Weiny <ira.weiny@intel.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Xiao Yang <yangx.jy@cn.fujitsu.com>, fstests@vger.kernel.org
Subject: Re: [PATCH v6 1/7] common/rc: Introduce new helpers for DAX mount options and FS_XFLAG_DAX
Date: Wed, 15 Jul 2020 11:00:11 -0700	[thread overview]
Message-ID: <20200715180008.GL3008823@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20200715155631.GL7600@magnolia>

On Wed, Jul 15, 2020 at 08:56:31AM -0700, Darrick J. Wong wrote:
> On Wed, Jul 15, 2020 at 01:55:14PM +0800, Xiao Yang wrote:
> > On 2020/7/15 12:15, Ira Weiny wrote:
> > > On Wed, Jul 15, 2020 at 11:19:58AM +0800, Xiao Yang wrote:
> > > > On 2020/7/15 9:59, Ira Weiny wrote:
> > > > > On Tue, Jul 14, 2020 at 05:40:03PM +0800, 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>
> > > > Hi Ira,
> > > > 
> > > > Do you want to check if invalid parameter is passed to
> > > > _require_scratch_dax_mountopt? Thought
> > > > I think it is not necessary(user should pass correct parament).
> > > > Like this:
> > > > [ "$mountopt" != "dax" ]&&  [ "$mountopt" != "dax=always" ]&&  _notrun
> > > > "$mountopt is invalid"
> > > I thought this patch was just checking if the filesystem/device supported DAX
> > > such that DAX tests could run using either old _or_ new dax support...
> > > But after thinking about it I think we need something more complicated.
> > > 
> > > Something like:
> > > 
> > > if ('-o dax=inode')
> > > 	// FS is DAX with per file support (ie ext4 || XFS kernel>= 5.8)
> > Hi Ira,
> > 
> > dax=inode/dax=never cannot check if underlying device supports dax, so I
> > perfer to use dax=always
> > For example:
> > XFS:
> > # mount -o dax=inode /dev/sda8 /mnt/xfstests/test/
> > # mount | grep sda8
> > /dev/sda8 on /mnt/xfstests/test type xfs
> > (rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota)
> > ...
> > # mount -o dax=always /dev/sda8 /mnt/xfstests/test/
> > # mount | grep sda8
> > /dev/sda8 on /mnt/xfstests/test type xfs
> > (rw,relatime,seclabel,attr2,dax=never,inode64,logbufs=8,logbsize=32k,noquota)
> > 
> > EXT4:
> > # mount -o dax=inode /dev/sda8 /mnt/xfstests/test/
> > # mount | grep sda8
> > /dev/sda8 on /mnt/xfstests/test type ext4 (rw,relatime,seclabel,dax=inode)
> > ...
> > # mount -o dax=always /dev/sda8 /mnt/xfstests/test/
> > mount: /mnt/xfstests/test: wrong fs type, bad option, bad superblock on
> > /dev/sda8, missing codepage or helper program, or other error.
> > # dmesg | grep DAX
> > [597988.165120] EXT4-fs (sda8): DAX unsupported by block device.
> > 
> > If we want to test new dax(i.e. dax=inode, dax=always or dax=never), so pass
> > "dax=always" to  _require_scratch_dax_mountopt
> > If we want to test old dax  or new dax=always(either of them), so pass "dax"
> > to _require_scratch_dax_mountopt
> 
> That does seem like the only way to figure out if a fs/device
> combination supports dax.
> 
> The valid arguments to the _require_scratch_dax* helpers are worth
> mentioning in a comment above the function, but I suspect that adding
> validation code is probably overkill.

Ok yes I see it now.

You are both correct.  I think a comment which indicates that one should pads
'-o dax' to check for 'old support' vs '-o dax=always' for 'new support' and
the test chooses which option to pass (based on the support it needs) to
_require_scratch_dax_mountopt()...

Sorry I was not completely following before!
Ira