[tip:perf/core] perf/live-mode: Handle payload-less events

[tip-bot for Tom Zanussi]

Commit-ID:  794e43b56c18b95fc9776c914a2659e7d558a352
Gitweb:     http://git.kernel.org/tip/794e43b56c18b95fc9776c914a2659e7d558a352
Author:     Tom Zanussi <tzanussi@xxxxxxxxx>
AuthorDate: Wed, 5 May 2010 00:27:40 -0500
Committer:  Frederic Weisbecker <fweisbec@xxxxxxxxx>
CommitDate: Sun, 9 May 2010 13:49:52 +0200

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@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
LKML-Reference: <1273038527.6383.51.camel@tropicana>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
---
 tools/perf/util/session.c |   19 +++++++++++--------
 1 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 9401909..00ab298 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 ||
--
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