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>

1 files changed, 11 insertions, 10 deletions

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 14db9f204b0a..d5359e3384e3 100644
--- 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;
 }