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

[Jiri Olsa]

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 <jo...@kernel.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