linux-kernel - Re: [PATCH] selftests/livepatch: adopt to newer sysctl error format

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Date:   Fri, 10 Jul 2020 17:27:35 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Shuah Khan <shuah@...nel.org>, live-patching@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/livepatch: adopt to newer sysctl error format

On Fri 2020-07-10 10:40:43, Kamalesh Babulal wrote:
> With procfs v3.3.16, the sysctl command doesn't prints the set key and
> value on error.  This change breaks livepatch selftest test-ftrace.sh,
> that tests the interaction of sysctl ftrace_enabled:
> 
>  # selftests: livepatch: test-ftrace.sh
>  # TEST: livepatch interaction with ftrace_enabled sysctl ... not ok
>  #
>  # --- expected
>  # +++ result
>  # @@ -16,7 +16,7 @@ livepatch: 'test_klp_livepatch': initial
>  #  livepatch: 'test_klp_livepatch': starting patching transition
>  #  livepatch: 'test_klp_livepatch': completing patching transition
>  #  livepatch: 'test_klp_livepatch': patching complete
>  # -livepatch: sysctl: setting key "kernel.ftrace_enabled": Device or
>     resource busy kernel.ftrace_enabled = 0
>  # +livepatch: sysctl: setting key "kernel.ftrace_enabled": Device or
>     resource busy
>  #  % echo 0 > /sys/kernel/livepatch/test_klp_livepatch/enabled
>  #  livepatch: 'test_klp_livepatch': initializing unpatching transition
>  #  livepatch: 'test_klp_livepatch': starting unpatching transition
>  #
>  # ERROR: livepatch kselftest(s) failed
> 
> on setting sysctl kernel.ftrace_enabled={0,1} value successfully, the
> set key and value is displayed.
> 
> This patch fixes it by limiting the output from both the cases to eight
> words, that includes the error message or set key and value on failure
> and success. The upper bound of eight words is enough to display the
> only tracked error message. Also, adjust the check_result string in
> test-ftrace.sh to match the expected output.

This looks really tricky.

I wonder if we could use "sysctl -q" to refuse printing the value
even with older versions. The following patch works here with
sysctl 3.3.15:

diff --git a/tools/testing/selftests/livepatch/functions.sh b/tools/testing/selftests/livepatch/functions.sh
index 2aab9791791d..47aa4c762bb4 100644
--- a/tools/testing/selftests/livepatch/functions.sh
+++ b/tools/testing/selftests/livepatch/functions.sh
@@ -64,7 +64,8 @@ function set_dynamic_debug() {
 }
 
 function set_ftrace_enabled() {
-	result=$(sysctl kernel.ftrace_enabled="$1" 2>&1 | paste --serial --delimiters=' ')
+	result=$(sysctl -q kernel.ftrace_enabled="$1" 2>&1 && \
+		 sysctl kernel.ftrace_enabled 2>&1)
 	echo "livepatch: $result" > /dev/kmsg
 }
 
diff --git a/tools/testing/selftests/livepatch/test-ftrace.sh b/tools/testing/selftests/livepatch/test-ftrace.sh
index e2a76887f40a..aa967c5d0558 100755
--- a/tools/testing/selftests/livepatch/test-ftrace.sh
+++ b/tools/testing/selftests/livepatch/test-ftrace.sh
@@ -53,7 +53,7 @@ livepatch: '$MOD_LIVEPATCH': initializing patching transition
 livepatch: '$MOD_LIVEPATCH': starting patching transition
 livepatch: '$MOD_LIVEPATCH': completing patching transition
 livepatch: '$MOD_LIVEPATCH': patching complete
-livepatch: sysctl: setting key \"kernel.ftrace_enabled\": Device or resource busy kernel.ftrace_enabled = 0
+livepatch: sysctl: setting key \"kernel.ftrace_enabled\": Device or resource busy
 % echo 0 > /sys/kernel/livepatch/$MOD_LIVEPATCH/enabled
 livepatch: '$MOD_LIVEPATCH': initializing unpatching transition
 livepatch: '$MOD_LIVEPATCH': starting unpatching transition


Best Regards,
Petr