perf evsel: Add overwrite attribute and check write_backward

Add 'overwrite' attribute to evsel to mark whether this event is
overwritable. The following commits will support syntax like:

  # perf record -e cycles/overwrite/ ...

An overwritable evsel requires kernel support for the
perf_event_attr.write_backward ring buffer feature.

Add it to perf_missing_feature.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1463762315-155689-2-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 14 insertions, 0 deletions

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 964c7c3602c0..02c177d14c8d 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -37,6 +37,7 @@ static struct {
         bool clockid;
         bool clockid_wrong;
         bool lbr_flags;
+        bool write_backward;
 } perf_missing_features;
 
 static clockid_t clockid;
@@ -1376,6 +1377,8 @@ fallback_missing_features:
         if (perf_missing_features.lbr_flags)
                 evsel->attr.branch_sample_type &= ~(PERF_SAMPLE_BRANCH_NO_FLAGS |
                                      PERF_SAMPLE_BRANCH_NO_CYCLES);
+        if (perf_missing_features.write_backward)
+                evsel->attr.write_backward = false;
 retry_sample_id:
         if (perf_missing_features.sample_id_all)
                 evsel->attr.sample_id_all = 0;
@@ -1438,6 +1441,12 @@ retry_open:
                                 err = -EINVAL;
                                 goto out_close;
                         }
+
+                        if (evsel->overwrite &&
+                            perf_missing_features.write_backward) {
+                                err = -EINVAL;
+                                goto out_close;
+                        }
                 }
         }
 
@@ -1500,6 +1509,10 @@ try_fallback:
                           PERF_SAMPLE_BRANCH_NO_FLAGS))) {
                 perf_missing_features.lbr_flags = true;
                 goto fallback_missing_features;
+        } else if (!perf_missing_features.write_backward &&
+                        evsel->attr.write_backward) {
+                perf_missing_features.write_backward = true;
+                goto fallback_missing_features;
         }
 
 out_close:
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 8a644fef452c..c1f10159804c 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -112,6 +112,7 @@ struct perf_evsel {
         bool                    tracking;
         bool                    per_pkg;
         bool                    precise_max;
+        bool                    overwrite;
         /* parse modifier helper */
         int                     exclude_GH;
         int                     nr_members;