linux-ext4 - Re: [PATCH] common/rc: Modify _require_batched

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Date:   Tue, 10 May 2022 14:32:23 +0800
From:   Zorro Lang <zlang@...hat.com>
To:     Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc:     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

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.

>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.

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