[PATCH v3 10/15] perf header: make write_pmu_mappings pipe-mode friendly

David Carrillo-Cisneros
2017-06-06T07:08:10Z

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>
---
tools/perf/util/header.c | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index f607c3c00f49..323ccd5df382 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -796,11 +796,19 @@ 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;
@@ -808,7 +816,6 @@ 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)
@@ -819,12 +826,6 @@ 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;