[PATCH 6/6] perf kmem: Show warning when trying to run stat without record

[Namhyung Kim <namhyung@xxxxxxxxxx>]

Sometimes one can mistakenly run perf kmem stat without perf kmem
record before or different configuration like recoding --slab and stat
--page.  Show a warning message like below to inform user:

  # perf kmem stat --page --caller
  Not found page events.  Have you run 'perf kmem record --page' before?

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 tools/perf/builtin-kmem.c | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/tools/perf/builtin-kmem.c b/tools/perf/builtin-kmem.c
index f0d018179e1c..ddb6ccb88b45 100644
--- a/tools/perf/builtin-kmem.c
+++ b/tools/perf/builtin-kmem.c
@@ -1882,6 +1882,7 @@ int cmd_kmem(int argc, const char **argv, const char *prefix __maybe_unused)
 	};
 	struct perf_session *session;
 	int ret = -1;
+	const char errmsg[] = "Not found %s events.  Have you run 'perf kmem record --%s' before?\n";
 
 	perf_config(kmem_config, NULL);
 	argc = parse_options_subcommand(argc, argv, kmem_options,
@@ -1908,11 +1909,35 @@ int cmd_kmem(int argc, const char **argv, const char *prefix __maybe_unused)
 	if (session == NULL)
 		return -1;
 
+	if (kmem_slab) {
+		struct perf_evsel *evsel;
+		bool found = false;
+
+		evlist__for_each(session->evlist, evsel) {
+			if (!strcmp(perf_evsel__name(evsel), "kmem:kmalloc")) {
+				found = true;
+				break;
+			}
+		}
+		if (!found) {
+			pr_err(errmsg, "slab", "slab");
+			return -1;
+		}
+	}
+
 	if (kmem_page) {
-		struct perf_evsel *evsel = perf_evlist__first(session->evlist);
+		struct perf_evsel *evsel;
+		bool found = false;
 
-		if (evsel == NULL || evsel->tp_format == NULL) {
-			pr_err("invalid event found.. aborting\n");
+		evlist__for_each(session->evlist, evsel) {
+			if (!strcmp(perf_evsel__name(evsel),
+				    "kmem:mm_page_alloc")) {
+				found = true;
+				break;
+			}
+		}
+		if (!found) {
+			pr_err(errmsg, "page", "page");
 			return -1;
 		}
 
-- 
2.3.4

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