perf/live-mode: Handle payload-less events

Some events, such as the PERF_RECORD_FINISHED_ROUND event consist of
only an event header and no data.  In this case, a 0-length payload
will be read, and the 0 return value will be wrongly interpreted as an
'unexpected end of event stream'.

This patch allows for proper handling of data-less events by skipping
0-length reads.

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
LKML-Reference: <1273038527.6383.51.camel@tropicana>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

1 files changed, 11 insertions, 8 deletions

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 9401909fa283..00ab298bbb4b 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -696,15 +696,18 @@ more:
         p = &event;
         p += sizeof(struct perf_event_header);
 
-        err = do_read(self->fd, p, size - sizeof(struct perf_event_header));
-        if (err <= 0) {
-                if (err == 0) {
-                        pr_err("unexpected end of event stream\n");
-                        goto done;
-                }
+        if (size - sizeof(struct perf_event_header)) {
+                err = do_read(self->fd, p,
+                              size - sizeof(struct perf_event_header));
+                if (err <= 0) {
+                        if (err == 0) {
+                                pr_err("unexpected end of event stream\n");
+                                goto done;
+                        }
 
-                pr_err("failed to read event data\n");
-                goto out_err;
+                        pr_err("failed to read event data\n");
+                        goto out_err;
+                }
         }
 
         if (size == 0 ||