perf test: Skip syscall enum test if no landlock syscall

The perf trace enum augmentation test specifically targets landlock_
add_rule syscall but IIUC it's an optional and can be opt-out by a
kernel config.

Currently trace_landlock() runs `perf test -w landlock` before the
actual testing to check the availability but it's not enough since the
workload always returns 0.  Instead it could check if perf trace output
has 'landlock' string.

Fixes: d66763f ("perf test trace_btf_enum: Add regression test for the BTF augmentation of enums in 'perf trace'")
Reviewed-by: Howard Chu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Namhyung Kim <[email protected]>

Author: namhyung

tools/perf/tests/shell/trace_btf_enum.sh

@@ -26,8 +26,12 @@ check_vmlinux() {
 trace_landlock() {
   echo "Tracing syscall ${syscall}"
 
-  # test flight just to see if landlock_add_rule and libbpf are available
-  $TESTPROG
+  # test flight just to see if landlock_add_rule is available
+  if ! perf trace $TESTPROG 2>&1 | grep -q landlock
+  then
+    echo "No landlock system call found, skipping to non-syscall tracing."
+    return
+  fi
 
   if perf trace -e $syscall $TESTPROG 2>&1 | \
      grep -q -E ".*landlock_add_rule\(ruleset_fd: 11, rule_type: (LANDLOCK_RULE_PATH_BENEATH|LANDLOCK_RULE_NET_PORT), rule_attr: 0x[a-f0-9]+, flags: 45\) = -1.*"