On Mon, 6 Jul 2020 18:47:14 +0300
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@xxxxxxxxx> wrote:
> The first record in a ring buffer page may not allways be at the
> beginning of the page. There could be time-extends injected before it.
> In this case kbuffer_start_of_data() will not return the first record,
> as expected. Additional filed "start" is added in kbuffer struct, to hold
> the offset of the first record from the page and kbuffer_start_of_data()
> is modified to use it.
Thanks Tzvetomir,
I'm going to add a comment that this was originally taken from code I
wrote, and you cleaned it up and made it presentable. That way it
states why there's the two signed-off-bys.
-- Steve
>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@xxxxxxxxx>
> ---
> lib/traceevent/kbuffer-parse.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/lib/traceevent/kbuffer-parse.c b/lib/traceevent/kbuffer-parse.c
> index 2c5f00a9..844db976 100644
> --- a/lib/traceevent/kbuffer-parse.c
> +++ b/lib/traceevent/kbuffer-parse.c
> @@ -35,6 +35,7 @@ enum {
> * @next - offset from @data to the start of next event
> * @size - The size of data on @data
> * @start - The offset from @subbuffer where @data lives
> + * @first - The offset from @subbuffer where the first non time stamp event lives
> *
> * @read_4 - Function to read 4 raw bytes (may swap)
> * @read_8 - Function to read 8 raw bytes (may swap)
> @@ -51,6 +52,7 @@ struct kbuffer {
> unsigned int next;
> unsigned int size;
> unsigned int start;
> + unsigned int first;
>
> unsigned int (*read_4)(void *ptr);
> unsigned long long (*read_8)(void *ptr);
> @@ -546,6 +548,9 @@ int kbuffer_load_subbuffer(struct kbuffer *kbuf, void *subbuffer)
>
> next_event(kbuf);
>
> + /* save the first record from the page */
> + kbuf->first = kbuf->curr;
> +
> return 0;
> }
>
> @@ -755,7 +760,7 @@ void kbuffer_set_old_format(struct kbuffer *kbuf)
> */
> int kbuffer_start_of_data(struct kbuffer *kbuf)
> {
> - return kbuf->start;
> + return kbuf->first + kbuf->start;
> }
>
> /**
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