linux-kernel - [PATCH 12/12] perf header: Use last modification time for timestamp

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Date:   Thu, 16 Jan 2020 10:48:14 -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,
        Michael Petlan <mpetlan@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 12/12] perf header: Use last modification time for timestamp

From: Michael Petlan <mpetlan@...hat.com>

Using .st_ctime clobbers the timestamp information in perf report header
whenever any operation is done with the file. Even tar-ing and untar-ing
the perf.data file (which preserves the file last modification timestamp)
doesn't prevent that:

    [Michael@...go tmp]$ ls -l perf.data
->	-rw-------. 1 Michael Michael 169888 Dec  2 15:23 perf.data

	[Michael@...go tmp]$ perf report --header-only
	# ========
->	# captured on    : Mon Dec  2 15:23:42 2019
	 [...]

	[Michael@...go tmp]$ tar c perf.data | xz > perf.data.tar.xz
	[Michael@...go tmp]$ mkdir aaa
	[Michael@...go tmp]$ cd aaa
	[Michael@...go aaa]$ xzcat ../perf.data.tar.xz | tar x
	[Michael@...go aaa]$ ls -l -a
	total 172
	drwxrwxr-x. 2 Michael Michael     23 Jan 14 11:26 .
	drwxrwxr-x. 6 Michael Michael   4096 Jan 14 11:26 ..
->	-rw-------. 1 Michael Michael 169888 Dec  2 15:23 perf.data

	[Michael@...go aaa]$ perf report --header-only
	# ========
->	# captured on    : Tue Jan 14 11:26:16 2020
	 [...]

When using .st_mtime instead, correct information is printed:

	[Michael@...go aaa]$ ~/acme/tools/perf/perf report --header-only
	# ========
->	# captured on    : Mon Dec  2 15:23:42 2019
	 [...]

Signed-off-by: Michael Petlan <mpetlan@...hat.com>
Acked-by: Jiri Olsa <jolsa@...nel.org>
LPU-Reference: 20200114104236.31555-1-mpetlan@...hat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/header.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 93ad27830e2b..4246e7447e54 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -2922,7 +2922,7 @@ int perf_header__fprintf_info(struct perf_session *session, FILE *fp, bool full)
 	if (ret == -1)
 		return -1;
 
-	stctime = st.st_ctime;
+	stctime = st.st_mtime;
 	fprintf(fp, "# captured on    : %s", ctime(&stctime));
 
 	fprintf(fp, "# header version : %u\n", header->version);
-- 
2.21.1