linux-kernel - Re: [PATCH] selftest: net: Fix error message if empty variable

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Message-ID: <ryyvwk64xplpvwozytdsfkyxls7sa3r4p4xpdqfhh6h2k4rdhl@chwwppzuvbop>
Date: Thu, 25 Sep 2025 14:40:47 +0200
From: Alessandro Zanni <alessandrozanni.dev@...il.com>
To: Simon Horman <horms@...nel.org>
Cc: Alessandro Zanni <alessandro.zanni87@...il.com>, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, shuah@...nel.org, 
	netdev@...r.kernel.org, linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftest: net: Fix error message if empty variable

On Thu, Sep 25, 2025 at 11:49:30AM +0100, Simon Horman wrote:
> On Thu, Sep 25, 2025 at 01:04:07AM +0200, Alessandro Zanni wrote:
> > Fix to avoid cases where the `res` shell variable is
> > empty in script comparisons.
> > 
> > The issue can be reproduced with the command:
> > make kselftest TARGETS=net
> > 
> > It solves the error:
> > ./tfo_passive.sh: line 98: [: -eq: unary operator expected
> > 
> > Signed-off-by: Alessandro Zanni <alessandro.zanni87@...il.com>
> > ---
> >  tools/testing/selftests/net/tfo_passive.sh | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/tools/testing/selftests/net/tfo_passive.sh b/tools/testing/selftests/net/tfo_passive.sh
> > index 80bf11fdc046..2655931b2396 100755
> > --- a/tools/testing/selftests/net/tfo_passive.sh
> > +++ b/tools/testing/selftests/net/tfo_passive.sh
> > @@ -95,7 +95,7 @@ wait
> >  res=$(cat $out_file)
> >  rm $out_file
> >  
> > -if [ $res -eq 0 ]; then
> > +if [ -n "$res" ] && [ $res -eq 0 ]; then
> >  	echo "got invalid NAPI ID from passive TFO socket"
> >  	cleanup_ns
> >  	exit 1
> 
> Hi Alessandro,
> 
> I'm not sure what $res can be in practice.
> But as it is the contents of $out_file (or more specifically,
> the stdout of running cat $outfile), in theory it could be anything.
> 
> So while your patch addresses one error case.
> I think there are others.
> 
> f.e. if res is not empty but not numeric, then we may see
> 
> bash: [: b: integer expression expected
> 
> Or if res contains a newline, then we may see
> 
> bash: [: too many arguments
> 
> 
> So I wonder if it is better to treat $res as a string,
> and quote it to avoid unexpected side effects.
> 
> [ "$res" = "0" ]

I'm not sure about the possible values in $res neither.
I assumed it was numeric because of the "-eq" operator but,
if it can be any value, a string comparison would be better.

I'm going to edit it.

Thanks,
Alessandro