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

From: Jiri Olsa
Date: Wed Dec 30 2020 - 06:10:42 EST


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@xxxxxxxxxx>
---
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