perf evlist: Introduce perf_evlist__mmap_cb_get()

Add the perf_evlist__mmap_cb_get() function to return 'struct perf_mmap'
object during perf_evlist__mmap_ops() call.

The array of 'struct mmap' is allocated via evlist__alloc_mmap(), in
this callback we simply returns pointer to the base object.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20191007125344.14268-20-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evlist.c

@@ -750,6 +750,29 @@ perf_evlist__mmap_cb_idx(struct perf_evlist *_evlist,
 	auxtrace_mmap_params__set_idx(&mp->auxtrace_mp, evlist, idx, per_cpu);
 }
 
+static struct perf_mmap*
+perf_evlist__mmap_cb_get(struct perf_evlist *_evlist, bool overwrite, int idx)
+{
+	struct evlist *evlist = container_of(_evlist, struct evlist, core);
+	struct mmap *maps = evlist->mmap;
+
+	if (overwrite) {
+		maps = evlist->overwrite_mmap;
+
+		if (!maps) {
+			maps = evlist__alloc_mmap(evlist, true);
+			if (!maps)
+				return NULL;
+
+			evlist->overwrite_mmap = maps;
+			if (evlist->bkw_mmap_state == BKW_MMAP_NOTREADY)
+				perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_RUNNING);
+		}
+	}
+
+	return &maps[idx].core;
+}
+
 static int evlist__mmap_per_cpu(struct evlist *evlist,
 				     struct mmap_params *mp)
 {
@@ -948,6 +971,7 @@ int evlist__mmap_ex(struct evlist *evlist, unsigned int pages,
 	};
 	struct perf_evlist_mmap_ops ops __maybe_unused = {
 		.idx = perf_evlist__mmap_cb_idx,
+		.get = perf_evlist__mmap_cb_get,
 	};
 
 	if (!evlist->mmap)