Re: [PATCH 0/1] Support PERF_SAMPLE_READ with inherit_stat

[Andi Kleen <ak@linux.intel.com>]

> I had considered that, but given currently this perf_event_attr
> configuration is not allowed, I assumed that it would require existing
> tools to add support which would in effect be an opt-in. Of course,
> adding a new flag to be explicit would be trivial enough if required.

That's fair. Makes sense.

> That said, the binary format for the mmap records / read() etc does not
> change so using an unmodified tool to parse the data file will give bad
> results. Therefore any workflow where "modified recording tool" can be
> combined with "older / unmodified parsing tool" will break. Not sure of
> the best way to handle this... presumably whenever a change is made to
> the perf record format, any workflow that allows old parsers to read
> new format data without version checks could fail? Admittedly this is a
> "looks the same but isn't" change so harder for tools devs to spot. Any
> suggestions?

For perf itself we can find something. It does a couple of checks, like
reserved bits in the perf_event_attr. For the general case of other
parsers it's unclear. I suppose could increment the magic identifier
to PERFILE3

-Andi