linux-kernel - [PATCH 17/28] perf ftrace: Improve error message about capability to use ftrace

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Date:   Wed, 14 Aug 2019 15:40:40 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
        Clark Williams <williams@...hat.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Igor Lubashev <ilubashe@...mai.com>,
        James Morris <jmorris@...ei.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Suzuki Poulouse <suzuki.poulose@....com>
Subject: [PATCH 17/28] perf ftrace: Improve error message about capability to use ftrace

From: Arnaldo Carvalho de Melo <acme@...hat.com>

If we link against libcap, then we can state that CAP_SYS_ADMIN is
needed, if not, fallback to telling the user it needs to be root, as was
before linking against libcap.

Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc: Igor Lubashev <ilubashe@...mai.com>
Cc: James Morris <jmorris@...ei.org>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Suzuki Poulouse <suzuki.poulose@....com>
Link: https://lkml.kernel.org/n/tip-hhnbjdo8r67054of9zm2kxtl@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/builtin-ftrace.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 01a5bb58eb04..1367bb5046a7 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -284,7 +284,13 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
 	};
 
 	if (!perf_cap__capable(CAP_SYS_ADMIN)) {
-		pr_err("ftrace only works for root!\n");
+		pr_err("ftrace only works for %s!\n",
+#ifdef HAVE_LIBCAP_SUPPORT
+		"users with the SYS_ADMIN capability"
+#else
+		"root"
+#endif
+		);
 		return -1;
 	}
 
-- 
2.21.0