linux-kernel - [PATCHv2] perf tools: Detect when pipe is passed as perf data

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Message-Id: <20201230110935.582332-1-jolsa@kernel.org>
Date:   Wed, 30 Dec 2020 12:09:35 +0100
From:   Jiri Olsa <jolsa@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Alexei Budankov <abudankov@...wei.com>
Subject: [PATCHv2] perf tools: Detect when pipe is passed as perf data

Currently we allow pipe input/output only through '-' string
being passed to '-o' or '-i' options, like:

  # mkfifo perf.pipe
  # perf record --no-buffering -e 'sched:sched_switch' -o - > perf.pipe &
  [1] 354406
  # cat perf.pipe | ./perf --no-pager script -i - | head -3
            perf 354406 [000] 168190.164921: sched:sched_switch: perf:354406..
     migration/0    12 [000] 168190.164928: sched:sched_switch: migration/0:..
            perf 354406 [001] 168190.164981: sched:sched_switch: perf:354406..
  ...

This patch detects if given path is pipe and set the perf data
object accordingly, so it's possible now to do above with:

  # mkfifo perf.pipe
  # perf record --no-buffering -e 'sched:sched_switch' -o perf.pipe &
  [1] 360188
  # perf --no-pager script -i ./perf.pipe | head -3
            perf 354442 [000] 168275.464895: sched:sched_switch: perf:354442..
     migration/0    12 [000] 168275.464902: sched:sched_switch: migration/0:..
            perf 354442 [001] 168275.464953: sched:sched_switch: perf:354442..

It's of course possible to combine any of above ways.

Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
v2:
  - removed O_CREAT|O_TRUNC flags from pipe's write end

 tools/perf/util/data.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
index f29af4fc3d09..4dfa9e0f2fec 100644
--- a/tools/perf/util/data.c
+++ b/tools/perf/util/data.c
@@ -159,7 +159,7 @@ int perf_data__update_dir(struct perf_data *data)
 	return 0;
 }
 
-static bool check_pipe(struct perf_data *data)
+static int check_pipe(struct perf_data *data)
 {
 	struct stat st;
 	bool is_pipe = false;
@@ -172,6 +172,15 @@ static bool check_pipe(struct perf_data *data)
 	} else {
 		if (!strcmp(data->path, "-"))
 			is_pipe = true;
+		else if (!stat(data->path, &st) && S_ISFIFO(st.st_mode)) {
+			int flags = perf_data__is_read(data) ?
+				    O_RDONLY : O_WRONLY;
+
+			fd = open(data->path, flags);
+			if (fd < 0)
+				return -EINVAL;
+			is_pipe = true;
+		}
 	}
 
 	if (is_pipe) {
@@ -190,7 +199,8 @@ static bool check_pipe(struct perf_data *data)
 		}
 	}
 
-	return data->is_pipe = is_pipe;
+	data->is_pipe = is_pipe;
+	return 0;
 }
 
 static int check_backup(struct perf_data *data)
@@ -344,8 +354,11 @@ static int open_dir(struct perf_data *data)
 
 int perf_data__open(struct perf_data *data)
 {
-	if (check_pipe(data))
-		return 0;
+	int err;
+
+	err = check_pipe(data);
+	if (err || data->is_pipe)
+		return err;
 
 	/* currently it allows stdio for pipe only */
 	data->use_stdio = false;
@@ -410,8 +423,10 @@ int perf_data__switch(struct perf_data *data,
 {
 	int ret;
 
-	if (check_pipe(data))
-		return -EINVAL;
+	ret = check_pipe(data);
+	if (ret || data->is_pipe)
+		return ret;
+
 	if (perf_data__is_read(data))
 		return -EINVAL;
 
-- 
2.26.2