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