[PATCH] selftests/livepatch: adopt to newer sysctl error format

[Kamalesh Babulal <kamalesh@xxxxxxxxxxxxxxxxxx>]

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.

With the patch, the test-ftrace.sh passes on v3.3.15, v3.3.16 versions
of sysctl:
 ...
 # selftests: livepatch: test-ftrace.sh
 # TEST: livepatch interaction with ftrace_enabled sysctl ... ok
 ok 5 selftests: livepatch: test-ftrace.sh

Signed-off-by: Kamalesh Babulal <kamalesh@xxxxxxxxxxxxxxxxxx>
---
Based on livepatching/for-5.9/selftests-cleanup, to be merged
through livepatching.git

 tools/testing/selftests/livepatch/functions.sh   | 3 ++-
 tools/testing/selftests/livepatch/test-ftrace.sh | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/livepatch/functions.sh b/tools/testing/selftests/livepatch/functions.sh
index 36648ca367c2..e3c0490d5a45 100644
--- a/tools/testing/selftests/livepatch/functions.sh
+++ b/tools/testing/selftests/livepatch/functions.sh
@@ -75,7 +75,8 @@ function set_dynamic_debug() {
 }
 
 function set_ftrace_enabled() {
-	result=$(sysctl kernel.ftrace_enabled="$1" 2>&1 | paste --serial --delimiters=' ')
+	result=$(sysctl kernel.ftrace_enabled="$1" 2>&1 | paste --serial --delimiters=' ' | \
+		 cut -d" " -f1-8)
 	echo "livepatch: $result" > /dev/kmsg
 }
 
diff --git a/tools/testing/selftests/livepatch/test-ftrace.sh b/tools/testing/selftests/livepatch/test-ftrace.sh
index 9160c9ec3b6f..552e165512f4 100755
--- a/tools/testing/selftests/livepatch/test-ftrace.sh
+++ b/tools/testing/selftests/livepatch/test-ftrace.sh
@@ -51,7 +51,7 @@ 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

base-commit: 3fd9bd8b7e41a1908bf8bc0cd06606f2b787cd39
-- 
2.26.2