linux-kernel - Re: [PATCH] common/rc: Modify _require_batched

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Date:   Tue, 10 May 2022 17:19:16 +0530
From:   Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To:     fstests@...r.kernel.org, riteshh@...ux.ibm.com,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] common/rc: Modify _require_batched_discard to improve
 test coverage

Hi Zorro,

Thanks for the review.

On Tue, May 10, 2022 at 02:32:23PM +0800, Zorro Lang wrote:
> On Fri, Apr 01, 2022 at 11:27:13AM +0530, Ojaswin Mujoo wrote:
> > A recent ext4 patch discussed [1] that some devices (eg LVMs) can
> > have a discard granularity as big as 42MB which makes it larger
> > than the group size of ext4 FS with 1k BS. This causes the FITRIM
> > IOCTL to fail on filesystems like ext4.
> > 
> > This case was not correctly handle by "_require_batched_discard" as
> > it incorrectly interpreted the FITRIM failure as fs not supporting
> > the IOCTL. This caused the tests like generic/260 to incorectly
> > report "not run" instead of "failed" in case of large discard
> > granularity.
> > 
> > Fix "_require_batched_discard" to use a more accurate method
> > to determine if discard is supported.
> > 
> > [1] commit 173b6e383d2
> >     ext4: avoid trim error on fs with small groups
> > 
> > Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> > ---
> >  common/rc | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/common/rc b/common/rc
> > index e2d3d72a..97386342 100644
> > --- a/common/rc
> > +++ b/common/rc
> > @@ -3858,7 +3858,13 @@ _require_batched_discard()
> >  		exit 1
> >  	fi
> >  	_require_fstrim
> > -	$FSTRIM_PROG $1 > /dev/null 2>&1 || _notrun "FITRIM not supported on $1"
> > +
> > +	$FSTRIM_PROG $1 2>&1 | grep -q "not supported"
> > +	RET=$?
> 
> Better to use global variable carefully in common functions, if it's not
> necessary, I'd recommend using "local ret" at here.
Sure, I'll make the change.

> 
> From my experience, the *quiet (-q)* grep does "exit_on_match" directly,
> it won't wait the write process, if the write process is still writing but
> the grep has exited, then it'll cause broken pipe, and the write process
> exit with failure.
> 
> It doesn't always happend, it depends. So I'd like to use "${PIPESTATUS[1]}"
> or write it as 'grep -q "not supported" <($FSTRIM_PROG $1 2>&1)', to make sure
> we just care about the "grep" result.
Ah makes sense, will make this change as well.

Regards,
Ojaswin
> 
> > +	if [ "$RET" = "0" ]
> > +	then
> > +		_notrun "FITRIM not supported on $1"
> > +	fi
> >  }
> >  
> >  _require_dumpe2fs()
> > -- 
> > 2.27.0
> > 
>