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    SubjectRe: [PATCH V5 09/12] perf: make events stream always parsable
    On 15/07/13 09:14, Adrian Hunter wrote:
    > On 12/07/13 17:55, Peter Zijlstra wrote:
    >> On Fri, Jul 12, 2013 at 03:56:01PM +0300, Adrian Hunter wrote:
    >>>> There's events where this isn't a possible location; take PERF_RECORD_MMAP for
    >>>> instance; the tail is the complete filename.
    >>>
    >>> PERF_RECORD_MMAP falls in the category I have called non-sample events.
    >>> Those events are appended with an ID sample. perf tools parses the ID
    >>> sample backwards from header.size. So the ID is at the last position
    >>> relative to header.size
    >>
    >> But why? Why make it different per PERF_RECORD type?
    >
    > There have always been two formats:
    >
    > 1. PERF_RECORD_SAMPLE as defined by perf_output_sample()
    >
    > 2. everything else as defined by __perf_event__output_id_sample()
    >
    > The two formats are not the same, and there is no reason for them to be.
    >
    > PERF_RECORD_SAMPLE is parsed forwards, so the ID is at the first position.
    >
    > ID samples are parsed backwards, so the ID is at the last position (i.e. the
    > first position parsed).

    If you want the ID at the first position in the ID sample, it is do-able.
    It means perf tools will have to be changed to calculate the variable start
    position of the ID sample, and then parse the ID sample forwards from there.
    Please advise.



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