diff mbox series

[v12,3/9] trace-cmd: Fix tracecmd_read_page_record() to read more than one event

Message ID 20190828085746.26231-4-tz.stoyanov@gmail.com (mailing list archive)
State Superseded
Headers show
Series trace-cmd: Timetamps sync between host and guest machines, relying on vsock events. | expand

Commit Message

Tzvetomir Stoyanov (VMware) Aug. 28, 2019, 8:57 a.m. UTC 
From: Tzvetomir Stoyanov <tstoyanov@vmware.com>

The kbuffer_next_event() will return the next event on the sub buffer.
If we pass in the last_record to tracecmd_read_page_record(), it
initializes the sub buffer, and by calling kbuffer_next_event()
(instead of kbuffer_read_event()), the second event on the sub buffer
is returned. This causes the match of the last_record not to match if
the last_record happens to be the first event on the sub buffer.

Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
---
 lib/trace-cmd/trace-input.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

Comments

Steven Rostedt Oct. 22, 2019, 5:34 p.m. UTC | #1 
On Wed, 28 Aug 2019 11:57:40 +0300
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com> wrote:

> From: Tzvetomir Stoyanov <tstoyanov@vmware.com>
> 
> The kbuffer_next_event() will return the next event on the sub buffer.
> If we pass in the last_record to tracecmd_read_page_record(), it
> initializes the sub buffer, and by calling kbuffer_next_event()
> (instead of kbuffer_read_event()), the second event on the sub buffer
> is returned. This causes the match of the last_record not to match if
> the last_record happens to be the first event on the sub buffer.

Bah, I see why this was done incorrectly. Good catch.

This should be added independent of this series.

Thanks!

-- Steve
diff mbox series

Patch

diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c
index 05e595f..3bb17f9 100644
--- a/lib/trace-cmd/trace-input.c
+++ b/lib/trace-cmd/trace-input.c
@@ -1720,18 +1720,22 @@  tracecmd_read_page_record(struct tep_handle *pevent, void *page, int size,
 			goto out_free;
 		}
 
-		do {
+		ptr = kbuffer_read_event(kbuf, &ts);
+		while (ptr < last_record->data) {
 			ptr = kbuffer_next_event(kbuf, NULL);
 			if (!ptr)
 				break;
-		} while (ptr < last_record->data);
+			if (ptr == last_record->data)
+				break;
+		}
 		if (ptr != last_record->data) {
 			warning("tracecmd_read_page_record: could not find last_record");
 			goto out_free;
 		}
-	}
+		ptr = kbuffer_next_event(kbuf, &ts);
+	} else
+		ptr = kbuffer_read_event(kbuf, &ts);
 
-	ptr = kbuffer_read_event(kbuf, &ts);
 	if (!ptr)
 		goto out_free;