perf: Use read() instead of lseek() in trace_event_read.c:skip()

This is a small fix for a problem affecting live-mode, introduced
recently:

root@tropicana:~# perf trace rwtop
perf trace started with Perl
script /root/libexec/perf-core/scripts/perl/rwtop.pl

  Fatal: did not read header event

commit d00a47cce569a3e660a8c9de5d57af28d6a9f0f7 added a skip()
function to skip over e.g. header_page, but this doesn't work for
live mode.  This patch re-implements skip() to use read() instead of
lseek() to fix that.

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1273032130.6383.28.camel@tropicana>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

1 files changed, 13 insertions, 6 deletions

diff --git a/tools/perf/util/trace-event-read.c b/tools/perf/util/trace-event-read.c
index cb54cd0..f55cc3a 100644
--- a/tools/perf/util/trace-event-read.c
+++ b/tools/perf/util/trace-event-read.c
@@ -53,12 +53,6 @@ static unsigned long	page_size;
 static ssize_t calc_data_size;
 static bool repipe;
 
-/* If it fails, the next read will report it */
-static void skip(int size)
-{
-	lseek(input_fd, size, SEEK_CUR);
-}
-
 static int do_read(int fd, void *buf, int size)
 {
 	int rsize = size;
@@ -98,6 +92,19 @@ static int read_or_die(void *data, int size)
 	return r;
 }
 
+/* If it fails, the next read will report it */
+static void skip(int size)
+{
+	char buf[BUFSIZ];
+	int r;
+
+	while (size) {
+		r = size > BUFSIZ ? BUFSIZ : size;
+		read_or_die(buf, r);
+		size -= r;
+	};
+}
+
 static unsigned int read4(void)
 {
 	unsigned int data;