[PATCH 35/46] perf record: Don't read from and poll overwrite channel

Wang Nan
2016-02-26T09:43:12Z

Reading from overwritable ring buffer is unreliable. Introduce
record__mmap_should_read() and prevent reading from overwrite ring
buffer in 'perf record'. The rule in record__mmap_should_read() will
be changed when perf support reading from backward writing ring buffer.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
tools/perf/builtin-record.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 92eccf1..120b3bb 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -462,6 +462,19 @@ static struct perf_event_header finished_round_event = {
.type = PERF_RECORD_FINISHED_ROUND,
};

+static bool record__mmap_should_read(struct record *rec, int idx)
+{
+ int channel = -1;
+
+ if (!rec->evlist->mmap[idx].base)
+ return false;
+ if (perf_evlist__channel_idx(rec->evlist, &channel, &idx))
+ return false;
+ if (perf_evlist__channel_check(rec->evlist, channel, RDONLY))
+ return false;
+ return true;
+}
+
static int record__mmap_read_all(struct record *rec)
{
u64 bytes_written = rec->bytes_written;
@@ -472,7 +485,7 @@ static int record__mmap_read_all(struct record *rec)
for (i = 0; i < total_mmaps; i++) {
struct auxtrace_mmap *mm = &rec->evlist->mmap[i].auxtrace_mmap;

- if (rec->evlist->mmap[i].base) {
+ if (record__mmap_should_read(rec, i)) {
if (record__mmap_read(rec, i) != 0) {
rc = -1;
goto out;
--
1.8.3.4