[RFC PATCH v3 33/37] perf bpf: Probe at kprobe points

Wang Nan
2015-05-17T11:00:02Z

In this patch, kprobe points are created using add_perf_probe_events.
Since all events are already grouped together in an array, calling
add_perf_probe_events() once creates all of them.

To ensure recover the system when existing, a bpf_unprobe() is also
provided and hooked to atexit(). Because all of events are in group
"perf_bpf_probe" (PERF_BPF_PROBE_GROUP), use 'perf_bpf_probe:*' string
to remove all of them should be a simple method. However, this also
introduces a constrain that only one instance of 'perf bpf' is allowed
to be active.

Due to the atexit hook, this patch must ensure bpf_unprobe() won't
error if it has been executed. A global flag 'is_probing' is used to
track probing state. bpf_unprobe() will do nothing if it is unset.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
---
tools/perf/builtin-bpf.c | 8 ++++++++
tools/perf/util/bpf-loader.c | 48 ++++++++++++++++++++++++++++++++++++++++++++
tools/perf/util/bpf-loader.h | 2 ++
3 files changed, 58 insertions(+)

diff --git a/tools/perf/builtin-bpf.c b/tools/perf/builtin-bpf.c
index e922921..95e0c65 100644
--- a/tools/perf/builtin-bpf.c
+++ b/tools/perf/builtin-bpf.c
@@ -157,10 +157,18 @@ static int cmd_bpf_record(int argc, const char **argv,
}
}

+ if (bpf_probe()) {
+ pr_err("bpf: failed to probe\n");
+ goto errout;
+ }
+
return start_bpf_record(argc, argv);
usage:
usage_with_options(bpf_record_usage, options);
return -1;
+errout:
+ bpf_clear();
+ return -1;
}

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index 3dc9b61..c820d1a 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -160,9 +160,57 @@ void bpf_clear(void)
{
size_t i;

+ bpf_unprobe();
for (i = 0; i < params.nr_events; i++)
clear_perf_probe_event(&params.event_array[i]);

for (i = 0; i < params.nr_objects; i++)
bpf_close_object(params.objects[i]);
}
+
+static bool is_probing = false;
+
+int bpf_unprobe(void)
+{
+ struct strlist *dellist;
+ int ret;
+
+ if (!is_probing)
+ return 0;
+
+ dellist = strlist__new(true, PERF_BPF_PROBE_GROUP ":*");
+ if (!dellist) {
+ pr_err("Failed to create dellist when unprobing\n");
+ return -ENOMEM;
+ }
+
+ ret = del_perf_probe_events(dellist);
+ strlist__delete(dellist);
+ if (ret < 0)
+ pr_err(" Error: failed to delete events: %s\n",
+ strerror(-ret));
+ else
+ is_probing = false;
+ return ret < 0 ? ret : 0;
+}
+
+static void bpf_unprobe_atexit(void)
+{
+ bpf_unprobe();
+}
+
+int bpf_probe(void)
+{
+ int err = add_perf_probe_events(params.event_array,
+ params.nr_events,
+ MAX_PROBES, 0);
+ /* add_perf_probe_events return negative when fail */
+ if (err < 0)
+ pr_err("bpf probe: failed to probe events\n");
+ else {
+ is_probing = true;
+ atexit(bpf_unprobe_atexit);
+ }
+
+ return err < 0 ? err : 0;
+}
diff --git a/tools/perf/util/bpf-loader.h b/tools/perf/util/bpf-loader.h
index 74eebc3..30dea2e 100644
--- a/tools/perf/util/bpf-loader.h
+++ b/tools/perf/util/bpf-loader.h
@@ -8,6 +8,8 @@
#define __BPF_LOADER_H

int bpf_prepare_load(const char *filename);
+int bpf_probe(void);
+int bpf_unprobe(void);

void bpf_clear(void);
#endif
--
1.8.3.4