linux-kernel - Re: [PATCH] xfs: fail dax mount if reflink is enabled on a partition

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Date:   Thu, 28 Jul 2022 21:54:12 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     "ruansy.fnst@...itsu.com" <ruansy.fnst@...itsu.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "david@...morbit.com" <david@...morbit.com>,
        "hch@...radead.org" <hch@...radead.org>
Subject: Re: [PATCH] xfs: fail dax mount if reflink is enabled on a partition

On Fri, Jul 29, 2022 at 03:55:24AM +0000, ruansy.fnst@...itsu.com wrote:
> 
> 
> 在 2022/7/22 0:16, Darrick J. Wong 写道:
> > On Thu, Jul 21, 2022 at 02:06:10PM +0000, ruansy.fnst@...itsu.com wrote:
> >> 在 2022/7/1 8:31, Darrick J. Wong 写道:
> >>> On Thu, Jun 09, 2022 at 10:34:35PM +0800, Shiyang Ruan wrote:
> >>>> Failure notification is not supported on partitions.  So, when we mount
> >>>> a reflink enabled xfs on a partition with dax option, let it fail with
> >>>> -EINVAL code.
> >>>>
> >>>> Signed-off-by: Shiyang Ruan <ruansy.fnst@...itsu.com>
> >>>
> >>> Looks good to me, though I think this patch applies to ... wherever all
> >>> those rmap+reflink+dax patches went.  I think that's akpm's tree, right?
> >>>
> >>> Ideally this would go in through there to keep the pieces together, but
> >>> I don't mind tossing this in at the end of the 5.20 merge window if akpm
> >>> is unwilling.
> >>
> >> BTW, since these patches (dax&reflink&rmap + THIS + pmem-unbind) are
> >> waiting to be merged, is it time to think about "removing the
> >> experimental tag" again?  :)
> > 
> > It's probably time to take up that question again.
> > 
> > Yesterday I tried running generic/470 (aka the MAP_SYNC test) and it
> > didn't succeed because it sets up dmlogwrites atop dmthinp atop pmem,
> > and at least one of those dm layers no longer allows fsdax pass-through,
> > so XFS silently turned mount -o dax into -o dax=never. :(
> 
> Hi Darrick,
> 
> I tried generic/470 but it didn't run:
>    [not run] Cannot use thin-pool devices on DAX capable block devices.
> 
> Did you modify the _require_dm_target() in common/rc?  I added thin-pool 
> to not to check dax capability:
> 
>          case $target in
>          stripe|linear|log-writes|thin-pool)  # add thin-pool here
>                  ;;
> 
> then the case finally ran and it silently turned off dax as you said.
> 
> Are the steps for reproduction correct? If so, I will continue to 
> investigate this problem.

Ah, yes, I did add thin-pool to that case statement.  Sorry I forgot to
mention that.  I suspect that the removal of dm support for pmem is
going to force us to completely redesign this test.  I can't really
think of how, though, since there's no good way that I know of to gain a
point-in-time snapshot of a pmem device.

--D

> 
> --
> Thanks,
> Ruan.
> 
> 
> 
> > 
> > I'm not sure how to fix that...
> > 
> > --D
> > 
> >>
> >> --
> >> Thanks,
> >> Ruan.
> >>
> >>>
> >>> Reviewed-by: Darrick J. Wong <djwong@...nel.org>
> >>>
> >>> --D
> >>>
> >>>> ---
> >>>>    fs/xfs/xfs_super.c | 6 ++++--
> >>>>    1 file changed, 4 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> >>>> index 8495ef076ffc..a3c221841fa6 100644
> >>>> --- a/fs/xfs/xfs_super.c
> >>>> +++ b/fs/xfs/xfs_super.c
> >>>> @@ -348,8 +348,10 @@ xfs_setup_dax_always(
> >>>>    		goto disable_dax;
> >>>>    	}
> >>>>    
> >>>> -	if (xfs_has_reflink(mp)) {
> >>>> -		xfs_alert(mp, "DAX and reflink cannot be used together!");
> >>>> +	if (xfs_has_reflink(mp) &&
> >>>> +	    bdev_is_partition(mp->m_ddev_targp->bt_bdev)) {
> >>>> +		xfs_alert(mp,
> >>>> +			"DAX and reflink cannot work with multi-partitions!");
> >>>>    		return -EINVAL;
> >>>>    	}
> >>>>    
> >>>> -- 
> >>>> 2.36.1
> >>>>
> >>>>
> >>>>