Re: [PATCH V9 09/14] perf: make events stream always parsable

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Aug 05, 2013 at 07:26:29PM +0300, Adrian Hunter wrote:
> The event stream is not always parsable because the format of a sample
> is dependent on the sample_type of the selected event.  When there
> is more than one selected event and the sample_types are not the
> same then parsing becomes problematic.  A sample can be matched to its
> selected event using the ID that is allocated when the event is opened.
> Unfortunately, to get the ID from the sample means first parsing it.
> 
> This patch adds a new sample format bit PERF_SAMPLE_IDENTIFER that puts
> the ID at a fixed position so that the ID can be retrieved without
> parsing the sample.  For sample events, that is the first position
> immediately after the header.  For non-sample events, that is the last
> position.
> 
> In this respect parsing samples requires that the sample_type and ID
> values are recorded.  For example, perf tools records struct perf_event_attr
> and the IDs within the perf.data file.  Those must be read first
> before it is possible to parse samples found later in the perf.data file.
> 
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>

Acked-by: Peter Zijlstra <peterz@infradead.org>