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ring-buffer: fix timestamp in partial ring_buffer_page_read

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If a partial ring_buffer_page_read happens, then some of the
incremental timestamps may be lost. This patch writes the
recent timestamp into the page that is passed back to the caller.

A partial ring_buffer_page_read is where the full page would not
be written back to the user, and instead, just part of the page
is copied to the user. A full page would be a page swap with the
ring buffer and the timestamps would be correct.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
This commit is contained in:
Steven Rostedt 2009-03-03 23:52:42 -05:00
parent e543ad7691
commit 4f3640f8a3
1 changed files with 5 additions and 1 deletions
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6
kernel/trace/ring_buffer.c
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@ -2461,6 +2461,7 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
unsigned long flags;
unsigned int commit;
unsigned int read;
u64 save_timestamp;
int ret = -1;
/*
@ -2515,6 +2516,9 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
if (len < size)
goto out;
/* save the current timestamp, since the user will need it */
save_timestamp = cpu_buffer->read_stamp;
/* Need to copy one event at a time */
do {
memcpy(bpage->data + pos, rpage->data + rpos, size);
@ -2531,7 +2535,7 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
/* update bpage */
local_set(&bpage->commit, pos);
bpage->time_stamp = rpage->time_stamp;
bpage->time_stamp = save_timestamp;
/* we copied everything to the beginning */
read = 0;