libbpf-tools/klockstat: no more rlimit bumping + add comment

The PR adding the libbpf-tools port of klockstat was sitting in a
mergeable state for some time. Meanwhile, libbpf stopped exposing
rlimit_memlock bumping API and now does the rlimit bump automatically if
necessary. So remove the bump_rlimit_memlock call and set libbpf strict
mode for this tool.

Also, add a comment (from @brho's PR summary in iovisor#3688) detailing the
differences in default behavior between the libbpf-tools and bcc-python
versions.

Signed-off-by: Dave Marchevsky <[email protected]>

libbpf-tools/klockstat.c

@@ -4,6 +4,12 @@
  * Based on klockstat from BCC by Jiri Olsa and others
  * 2021-10-26 Barret Rhoden Created this.
  */
+/* Differences from BCC python tool:
+ * - can specify a lock by ksym name, using '-L'
+ * - tracks whichever task had the max time for acquire and hold, outputted
+ * when '-s' > 1 (otherwise it's cluttered).
+ * - does not reset stats each interval by default. Can request with -R.
+ */
 #include <argp.h>
 #include <errno.h>
 #include <signal.h>
@@ -484,12 +490,7 @@ int main(int argc, char **argv)
 
  sigaction(SIGINT, &sigact, 0);
 
- err = bump_memlock_rlimit();
- if (err) {
- warn("failed to increase rlimit: %d\n", err);
- err = 1;
- goto cleanup;
- }
+ libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
 
  ksyms = ksyms__load();
  if (!ksyms) {