Re: [PATCH] xfs/013: fix ENOSPC handling

[Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

On Jun 16, 2026 / 04:23, Zorro Lang wrote:
> On Mon, Jun 15, 2026 at 09:12:57PM +0900, Shin'ichiro Kawasaki wrote:
> > Commit 000813899afb ("fstests: scale some tests for high CPU count
> > sanity") replaced "touch" with "echo -n >" to speed up file creation by
> > using a shell builtin redirection instead of forking and execing an
> > external binary. However, this broke the ENOSPC filtering the test
> > relies on.
> > 
> > When the scratch filesystem fills up, the shell redirection "> $dir/$i"
> > fails instead of the "touch" command. The shell applies redirections
> > left-to-right, so "> $dir/$i" is attempted before "2>&1". Because
> > opening the file fails immediately with ENOSPC, the command never runs
> > and the shell writes the error message "No space left on device" to the
> > stderr instead of the pipe. Then the error message is not passed to
> > "filter_enospc" and leaks into the test output, causing the test case
> > failure. The failure is recreated by running the test case with rather
> > small size of block devices, such as 128MiB null_blk:
> > 
> > xfs/013            - output mismatch (see /home/test/xfstests/results//xfs/013.out.bad)
> >     --- tests/xfs/013.out	2026-05-28 16:52:16.881159200 +0900
> >     +++ /home/test/xfstests/results//xfs/013.out.bad	2026-06-11 17:20:36.269003467 +0900
> >     @@ -5,3 +5,12305 @@
> >      naming   =VERN bsize=XXX
> >      log      =LDEV bsize=XXX blocks=XXX
> >      realtime =RDEV extsz=XXX blocks=XXX, rtextents=XXX
> >     +/home/test/xfstests/tests/xfs/013: line 45: /var/scratch/dir2/19013: No space left on device
> >     +/home/test/xfstests/tests/xfs/013: line 45: /var/scratch/dir2/6452: No space left on device
> >     +/home/test/xfstests/tests/xfs/013: line 45: /var/scratch/dir2/14964: No space left on device
> >     +/home/test/xfstests/tests/xfs/013: line 45: /var/scratch/dir2/10051: No space left on device
> >     ...
> >     (Run 'diff -u /home/test/xfstests/tests/xfs/013.out /home/test/xfstests/results//xfs/013.out.bad'  to see the entire diff)
> > 
> > To fix the ENOSPC handling, wrap the redirection in a brace group so
> > that "2>&1" is applied to the group before the inner redirection is
> > attempted. The redirection failure is then written to the group's
> > stderr, which is piped into "filter_enospc". This keeps the faster
> > builtin file creation than the "touch" command as the trigger commit
> > intended.
> > 
> > Fixes: 000813899afb ("fstests: scale some tests for high CPU count sanity")
> > Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> > ---
> >  tests/xfs/013 | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tests/xfs/013 b/tests/xfs/013
> > index fd011445..2e9b9850 100755
> > --- a/tests/xfs/013
> > +++ b/tests/xfs/013
> > @@ -28,7 +28,7 @@ _create()
> >  	mkdir -p $dir
> >  	for i in $(seq 0 $count)
> >  	do
> > -		echo -n > $dir/$i 2>&1 | filter_enospc
> > +		{ echo -n > $dir/$i ; } 2>&1 | filter_enospc
> >  	done
> >  }
> >  
> > @@ -42,7 +42,7 @@ _rand_replace()
> >  	do
> >  		file=$((RANDOM % count))
> >  		rm -f $dir/$file
> > -		echo -n > $dir/$file 2>&1 | filter_enospc
> > +		{ echo -n > $dir/$file ; } 2>&1 | filter_enospc
> 
> Although I always use `(echo -n > $dir/$file) 2>&1` to deal with this kind of
> problem, this *Command Grouping* way is good to me too :)

Usually, I don't care much about the choice between parentheses or curly braces
for command grouping, but I chose curly braces here to avoid the cost of
creating sub-shells. It should be less overhead than parentheses that create
sub-shells. I guess the trigger commit wanted to reduce the overhead of the
process fork by "touch" commands, then I think curly braces are more consistent
here to keep the overhead smaller.

> 
> Reviewed-by: Zorro Lang <zlang@kernel.org>

Thanks!