perf evlist: Introduce backward_mmap array for evlist

Add backward_mmap to evlist, free it together with normal mmap.

Improve perf_evlist__pick_pc(), search backward_mmap if evlist->mmap is
not available.

This patch doesn't alloc this array. It will be allocated conditionally
in the following commits.

Signed-off-by: Wang Nan <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Cc: He Kuang <[e-mail]>
Cc: Masami Hiramatsu <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Nilay Vaish <[e-mail]>
Cc: Zefan Li <[e-mail]>
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-record.c

···
 	if (!evlist)
 		return 0;
 
-	maps = evlist->mmap;
+	maps = backward ? evlist->backward_mmap : evlist->mmap;
 	if (!maps)
 		return 0;
 
···
 static const struct perf_event_mmap_page *
 perf_evlist__pick_pc(struct perf_evlist *evlist)
 {
-	if (evlist && evlist->mmap && evlist->mmap[0].base)
-		return evlist->mmap[0].base;
+	if (evlist) {
+		if (evlist->mmap && evlist->mmap[0].base)
+			return evlist->mmap[0].base;
+		if (evlist->backward_mmap && evlist->backward_mmap[0].base)
+			return evlist->backward_mmap[0].base;
+	}
 	return NULL;
 }
 

tools/perf/util/evlist.c

···
 void perf_evlist__exit(struct perf_evlist *evlist)
 {
 	zfree(&evlist->mmap);
+	zfree(&evlist->backward_mmap);
 	fdarray__exit(&evlist->pollfd);
 }
 
···
 {
 	int i;
 
-	if (evlist->mmap == NULL)
-		return;
+	if (evlist->mmap)
+		for (i = 0; i < evlist->nr_mmaps; i++)
+			perf_mmap__munmap(&evlist->mmap[i]);
 
-	for (i = 0; i < evlist->nr_mmaps; i++)
-		perf_mmap__munmap(&evlist->mmap[i]);
+	if (evlist->backward_mmap)
+		for (i = 0; i < evlist->nr_mmaps; i++)
+			perf_mmap__munmap(&evlist->backward_mmap[i]);
 }
 
 void perf_evlist__munmap(struct perf_evlist *evlist)
 {
 	perf_evlist__munmap_nofree(evlist);
 	zfree(&evlist->mmap);
+	zfree(&evlist->backward_mmap);
 }
 
 static struct perf_mmap *perf_evlist__alloc_mmap(struct perf_evlist *evlist)

tools/perf/util/evlist.h

···
 	} workload;
 	struct fdarray	 pollfd;
 	struct perf_mmap *mmap;
+	struct perf_mmap *backward_mmap;
 	struct thread_map *threads;
 	struct cpu_map	  *cpus;
 	struct perf_evsel *selected;