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

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Message-ID: <20250925104930.GG836419@horms.kernel.org>
Date: Thu, 25 Sep 2025 11:49:30 +0100
From: Simon Horman <horms@...nel.org>
To: Alessandro Zanni <alessandro.zanni87@...il.com>
Cc: 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 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" ]