netdev - Re: [PATCH net-next 02/12] selftests/vsock: make wait_for

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Message-ID: <aP+yKDYZR6+/kzI2@devvm11784.nha0.facebook.com>
Date: Mon, 27 Oct 2025 10:55:52 -0700
From: Bobby Eshleman <bobbyeshleman@...il.com>
To: Simon Horman <horms@...nel.org>
Cc: Stefano Garzarella <sgarzare@...hat.com>, Shuah Khan <shuah@...nel.org>,
	Jakub Kicinski <kuba@...nel.org>, virtualization@...ts.linux.dev,
	netdev@...r.kernel.org, linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bobby Eshleman <bobbyeshleman@...a.com>
Subject: Re: [PATCH net-next 02/12] selftests/vsock: make wait_for_listener()
 work even if pipefail is on

On Mon, Oct 27, 2025 at 04:48:28PM +0000, Simon Horman wrote:
> On Wed, Oct 22, 2025 at 06:00:06PM -0700, Bobby Eshleman wrote:
> > From: Bobby Eshleman <bobbyeshleman@...a.com>
> > 
> > Save/restore pipefail to not mistakenly trip the if-condition
> > in wait_for_listener().
> > 
> > awk doesn't gracefully handle SIGPIPE with a non-zero exit code, so grep
> > exiting upon finding a match causes false-positives when the pipefail
> > option is used. This will enable pipefail usage, so that we can losing
> > failures when piping test output into log() functions.
> > 
> > Fixes: a4a65c6fe08b ("selftests/vsock: add initial vmtest.sh for vsock")
> > Signed-off-by: Bobby Eshleman <bobbyeshleman@...a.com>
> > ---
> >  tools/testing/selftests/vsock/vmtest.sh | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/vsock/vmtest.sh b/tools/testing/selftests/vsock/vmtest.sh
> > index 561600814bef..ec3ff443f49a 100755
> > --- a/tools/testing/selftests/vsock/vmtest.sh
> > +++ b/tools/testing/selftests/vsock/vmtest.sh
> > @@ -243,6 +243,7 @@ wait_for_listener()
> >  	local port=$1
> >  	local interval=$2
> >  	local max_intervals=$3
> > +	local old_pipefail
> >  	local protocol=tcp
> >  	local pattern
> >  	local i
> > @@ -251,6 +252,13 @@ wait_for_listener()
> >  
> >  	# for tcp protocol additionally check the socket state
> >  	[ "${protocol}" = "tcp" ] && pattern="${pattern}0A"
> > +
> > +	# 'grep -q' exits on match, sending SIGPIPE to 'awk', which exits with
> > +	# an error, causing the if-condition to fail when pipefail is set.
> > +	# Instead, temporarily disable pipefail and restore it later.
> > +	old_pipefail=$(set -o | awk '/^pipefail[[:space:]]+(on|off)$/{print $2}')
> > +	set +o pipefail
> > +
> >  	for i in $(seq "${max_intervals}"); do
> >  		if awk '{print $2" "$4}' /proc/net/"${protocol}"* | \
> >  		   grep -q "${pattern}"; then
> 
> Hi Bobby,
> 
> I agree this is a problem. But I'm wondering if you considered
> moving the pattern matching into the awk script. I'm no awk expert.
> But suspect that would lead to a more elegant solution.
> 

I bet you are right.

Playing around with awk, I find that this seems to work:

$ pattern=":$(printf '%04X' ${port}) 0A"
$ awk -v pattern="${pattern}" 'BEGIN {rc=1} $2" "$4 ~ pattern {rc=0}
	END {exit rc}' /proc/net/tcp && echo FOUND

I think it beats doing the save/restore on pipefail?

Best,
Bobby