Re: [PATCH v4 1/3] perf: add PERF_RECORD_NAMESPACES to include namespaces related info

[Hari Bathini]

On Wednesday 21 December 2016 06:54 PM, Peter Zijlstra wrote:
> On Wed, Dec 21, 2016 at 06:39:01PM +0530, Hari Bathini wrote:
> > Hi Peter,
> > > I don't see how the tool can parse old records (with NAMESPACES_MAX ==
> > > 7) if you set its NAMESPACES_MAX to say 10.
> > >
> > > Then it will expect the link_info array to be 10 entries and either read
> > > past the end of the record (if !sample_all) or try and interpret
> > > sample_id as link_info records.
> > Right. There will be inconsistency with data the perf tool tries to read
> > beyond
> > what the kernel supports. IIUC, you mean, include nr_namespaces field in the
> > record and warn the user if it doesn't match with the one perf-tool supports
> > before proceeding..?
> Yes, if you add a nr_namespaces field its always parsable. If an old
> tool finds more namespace than it has 'names' for it can always display
> the raw index number. If a new tool finds the array short, it will not
> display the missing ones.

Sure, Peter. Will post the next version as soon as
I am back from vacation..

Thanks
Hari