Re: [PATCH] perf session: Try to read pipe data from file

[Jiri Olsa]

On Fri, May 01, 2020 at 01:34:47PM +0200, Jiri Olsa wrote:
> From: Jiri Olsa <jo...@redhat.com>
> 
> Ian came with the idea of having support to read the pipe
> data also from file [1]. Currently pipe mode files fails
> like:
> 
>   $ perf record -o - sleep 1 > /tmp/perf.pipe.data
>   $ perf report -i /tmp/perf.pipe.data
>   incompatible file format (rerun with -v to learn more)
> 
> This patch adds the support to do that by trying the pipe
> header first, and if its successfully detected, switching
> the perf data to pipe mode.
> 
> [1] https://lore.kernel.org/lkml/20200409185744.255881-1-irog...@google.com/
> Original-patch-by: Ian Rogers <irog...@google.com>
> Signed-off-by: Jiri Olsa <jo...@kernel.org>

actualy.. I found another issue while trying this on tracepoints:

  # ./perf record -g  -e 'raw_syscalls:sys_enter' -o -  true > data
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.000 MB - ]
  # ./perf script -i ./data
  perf_event__process_tracing_data: tracing data size mismatch0x1034 [0xc]: 
failed to process type: 66

it's because some of the pipe synthesize code calls lseek, which
fails on pipe, but succeeds on normal file (with pipe data)

patch below fixes that for me, but I wonder there are other leftovers
like this.. I'll check on post it all together

jirka


---
diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 8ca709f938b8..33e299674121 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -3955,13 +3955,8 @@ int perf_event__process_tracing_data(struct perf_session 
*session,
 {
        ssize_t size_read, padding, size = event->tracing_data.size;
        int fd = perf_data__fd(session->data);
-       off_t offset = lseek(fd, 0, SEEK_CUR);
        char buf[BUFSIZ];
 
-       /* setup for reading amidst mmap */
-       lseek(fd, offset + sizeof(struct perf_record_header_tracing_data),
-             SEEK_SET);
-
        size_read = trace_report(fd, &session->tevent,
                                 session->repipe);
        padding = PERF_ALIGN(size_read, sizeof(u64)) - size_read;
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index c11d89e0ee55..b75df19feaf1 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1543,7 +1543,8 @@ static s64 perf_session__process_user_event(struct 
perf_session *session,
                return 0;
        case PERF_RECORD_HEADER_TRACING_DATA:
                /* setup for reading amidst mmap */
-               lseek(fd, file_offset, SEEK_SET);
+               if (!perf_data__is_pipe(session->data))
+                       lseek(fd, file_offset, SEEK_SET);
                return tool->tracing_data(session, event);
        case PERF_RECORD_HEADER_BUILD_ID:
                return tool->build_id(session, event);