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

[Wang Nan]

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 <wangn...@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

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