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

[Wang Nan]

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 <wangn...@huawei.com>
Signed-off-by: He Kuang <heku...@huawei.com>
Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
Cc: Jiri Olsa <jo...@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu...@hitachi.com>
Cc: Namhyung Kim <namhy...@kernel.org>
Cc: Zefan Li <lize...@huawei.com>
Cc: pi3or...@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