Re: [PATCH v2] fstests: generic/733: avoid output difference due to bash's version

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Sep 05, 2025 at 07:14:15AM +0930, Qu Wenruo wrote:
> [FALSE ALERT]
> When running generic/733 with bash 5.3.3 (any thing newer than 5.3.0
> will reproduce the bug), the test case will fail like the following:
> 
> generic/733 19s ... - output mismatch (see /home/adam/xfstests/results//generic/733.out.bad)
>     --- tests/generic/733.out	2025-09-04 17:30:08.568000000 +0930
>     +++ /home/adam/xfstests/results//generic/733.out.bad	2025-09-04 17:30:32.898475103 +0930
>     @@ -2,5 +2,5 @@
>      Format and mount
>      Create a many-block file
>      Reflink the big file
>     -Terminated
>     +Terminated                 $here/src/t_reflink_read_race "$testdir/file1" "$testdir/file2" "$testdir/outcome" &>> $seqres.full
>      test completed successfully
>     ...
>     (Run 'diff -u /home/adam/xfstests/tests/generic/733.out /home/adam/xfstests/results//generic/733.out.bad'  to see the entire diff)
> 
> [CAUSE]
> The failure is fs independent, but bash version dependent.
> 
> In bash v5.3.x, the job control will output the command which triggered
> the job control (from termination to core dump etc).
> 
> The "Terminated" message is not from the program, but from bash's job
> control, thus redirection won't hide that message.
> 
> [FIX]
> Run the command in a command group, which will be executed in a
> subshell.
> 
> By this we can redirect the output of the subshell, including the job
> control message, thus hide the different output pattern caused by
> different bash versions.
> 
> Thankfully this particular test case does extra checks on the outcome
> file to determine if the program is properly terminated, thus we are
> safe to move the "Terminated" line from the golden output to
> seqres.full.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> v2:
> - Use command grouping instead of background execution
>   Background execution requires extra cleanup to wait for the background
>   program.
>   Meanwhile command grouping will run in a subshell thus we can redirect
>   everything including the job control message.
> 
>   Thanks Darrick for pointing this solution out.
> ---
>  tests/generic/733     | 17 +++++++++++++++--
>  tests/generic/733.out |  1 -
>  2 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/tests/generic/733 b/tests/generic/733
> index aa7ad994..21347d51 100755
> --- a/tests/generic/733
> +++ b/tests/generic/733
> @@ -70,8 +70,21 @@ done
>  echo "fnr=$fnr" >> $seqres.full
>  
>  echo "Reflink the big file"
> -$here/src/t_reflink_read_race "$testdir/file1" "$testdir/file2" \
> -	"$testdir/outcome" &>> $seqres.full
> +# Workaround the default job control by command grouping so that we can redirect
> +# the job control message of the subshell.
> +#
> +# Job control of bash v5.3.x will output the command which triggered the job
> +# control (terminated, core dump etc).
> +# And since it's handled by bash itself, redirection of the program won't work
> +# for the job control message.
> +#
> +# Running the command in a command group will make the program run in a subshell
> +# so that we can direct the job control message of the subshell.
> +#
> +# We will check the outcome file to determine if the program is properly
> +# terminated, thus no need to bother the job control message.
> +{ $here/src/t_reflink_read_race "$testdir/file1" "$testdir/file2" \
> +	"$testdir/outcome" ; } &>> $seqres.full

/me wonders how many more of these bash messages are lurking out there,
but in the meantime

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

>  
>  if [ ! -e "$testdir/outcome" ]; then
>  	echo "Could not set up program"
> diff --git a/tests/generic/733.out b/tests/generic/733.out
> index d4f5a7c7..2383cc8d 100644
> --- a/tests/generic/733.out
> +++ b/tests/generic/733.out
> @@ -2,5 +2,4 @@ QA output created by 733
>  Format and mount
>  Create a many-block file
>  Reflink the big file
> -Terminated
>  test completed successfully
> -- 
> 2.51.0
> 
>