perf header: Make write_pmu_mappings pipe-mode friendly

In pipe-mode, we will operate over a buffer instead of a file descriptor
but write_pmu_mappings uses lseek to move over the perf.data file.

Refactor write_pmu_mappings to avoid the usage of lseek and allow
reusing the same logic in pipe-mode (next patch).

Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
Acked-by: David Ahern <dsahern@gmail.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Simon Que <sque@chromium.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20170718042549.145161-12-davidcc@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 14db9f204b0ace56167fa47a628cead17b1b94da..d5359e3384e33eb28159fc3c11245d45edf2a803 100644 (file)
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -797,11 +797,19 @@ static int write_pmu_mappings(struct feat_fd *ff,
                              struct perf_evlist *evlist __maybe_unused)
 {
        struct perf_pmu *pmu = NULL;
-       off_t offset = lseek(ff->fd, 0, SEEK_CUR);
-       __u32 pmu_num = 0;
+       u32 pmu_num = 0;
        int ret;
 
-       /* write real pmu_num later */
+       /*
+        * Do a first pass to count number of pmu to avoid lseek so this
+        * works in pipe mode as well.
+        */
+       while ((pmu = perf_pmu__scan(pmu))) {
+               if (!pmu->name)
+                       continue;
+               pmu_num++;
+       }
+
        ret = do_write(ff, &pmu_num, sizeof(pmu_num));
        if (ret < 0)
                return ret;
@@ -809,7 +817,6 @@ static int write_pmu_mappings(struct feat_fd *ff,
        while ((pmu = perf_pmu__scan(pmu))) {
                if (!pmu->name)
                        continue;
-               pmu_num++;
 
                ret = do_write(ff, &pmu->type, sizeof(pmu->type));
                if (ret < 0)
@@ -820,12 +827,6 @@ static int write_pmu_mappings(struct feat_fd *ff,
                        return ret;
        }
 
-       if (pwrite(ff->fd, &pmu_num, sizeof(pmu_num), offset) != sizeof(pmu_num)) {
-               /* discard all */
-               lseek(ff->fd, offset, SEEK_SET);
-               return -1;
-       }
-
        return 0;
 }