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perf probe: Fix usage when libtraceevent is missing

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While parsing the tracepoint events in parse_events_add_tracepoint()
function, code checks for HAVE_LIBTRACEEVENT support. This is needed
since libtraceevent is necessary for tracepoint. But while adding probe
points, check for LIBTRACEEVENT is not done in case of perf probe.
Hence, in environment with missing libtraceevent-devel, it is observed
that adding a probe point shows below message though it can't be used
via perf record.

Example:

Adding probe point:
	./perf probe 'vfs_getname=getname_flags:72 pathname=result->name:string'
	Added new event:
	  probe:vfs_getname    (on getname_flags:72 with pathname=result->name:string)

	You can now use it in all perf tools, such as:

		perf record -e probe:vfs_getname -aR sleep 1

But trying perf record:
	./perf  record -e probe:vfs_getname -aR sleep 1
	event syntax error: 'probe:vfs_getname'
				\___ unsupported tracepoint
	libtraceevent is necessary for tracepoint support
	Run 'perf list' for a list of valid events

The builtin tool like perf record needs libtraceevent to
parse tracefs. But still the probe can be used by enabling
via tracefs. Patch fixes the probe usage message to the user
based on presence of libtraceevent. With the fix,

 # ./perf probe 'pmu:myprobe=schedule'
 Added new event:
   pmu:myprobe          (on schedule)

 perf is not linked with libtraceevent, to use the new probe you can use tracefs:

	cd /sys/kernel/tracing/
	echo 1 > events/pmu/myprobe/enable
	echo 1 > tracing_on
	cat trace_pipe
	Before removing the probe, echo 0 > events/pmu/myprobe/enable

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Disha Goel <disgoel@linux.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nageswara R Sastry <rnsastry@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20230131134748.54567-1-atrajeev@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Athira Rajeev 2023-01-31 19:17:48 +05:30 committed by Arnaldo Carvalho de Melo
parent ce4c8e7966
commit 3980ee9ad8
1 changed files with 9 additions and 0 deletions
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9
tools/perf/builtin-probe.c
View file

@ -383,9 +383,18 @@ static int perf_add_probe_events(struct perf_probe_event *pevs, int npevs)
/* Note that it is possible to skip all events because of blacklist */
if (event) {
#ifndef HAVE_LIBTRACEEVENT
pr_info("\nperf is not linked with libtraceevent, to use the new probe you can use tracefs:\n\n");
pr_info("\tcd /sys/kernel/tracing/\n");
pr_info("\techo 1 > events/%s/%s/enable\n", group, event);
pr_info("\techo 1 > tracing_on\n");
pr_info("\tcat trace_pipe\n");
pr_info("\tBefore removing the probe, echo 0 > events/%s/%s/enable\n", group, event);
#else
/* Show how to use the event. */
pr_info("\nYou can now use it in all perf tools, such as:\n\n");
pr_info("\tperf record -e %s:%s -aR sleep 1\n\n", group, event);
#endif
}
out_cleanup: