Re: [PATCH] perf_counter: extensible perf_counter_attr

[Corey Ashford]

Peter Zijlstra wrote:
> On Mon, 2009-06-08 at 12:02 -0700, Corey Ashford wrote:
> > Hi Peter,
> >
> > Peter Zijlstra wrote:
> > > Allow extending the perf_counter_attr structure by linking extended
> > > structures to it.
> > >
> > > Also, should we grow the directly reserved space in the structure a
> > > little more?
> > >
> > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> > > ---
> > >  include/linux/perf_counter.h |    7 +++++++
> > >  kernel/perf_counter.c        |    1 +
> > >  2 files changed, 8 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
> > > index 3586df8..781d8ce 100644
> > > --- a/include/linux/perf_counter.h
> > > +++ b/include/linux/perf_counter.h
> > > @@ -175,6 +175,13 @@ struct perf_counter_attr {
> > >  	__u32			__reserved_3;
> > >
> > >  	__u64			__reserved_4;
> > > +
> > > +	struct perf_counter_attr_ext *ext_attrs;
> > > +};
> > > +
> > > +struct perf_counter_attr_ext {
> > > +	struct perf_counter_attr_ext 	*next;
> > > +	__u64				perf_attr_ext_type;
> > >  };
> > Let's say I want to extend the attributes by four 64-bit quantities... from the 
> > above definition, I'd need four additional records chained together, right?  How 
> > about something like this instead:
>
> Ah, the idea was to do something like:
>
> struct perf_counter_attr_feature {
> 	struct perf_counter_attr_ext	head;
> 	... more stuff ...
> };
>
> and set head.perf_attr_ext_type = PERF_ATTR_EXT_FEATURE


So you'd do something like this then when assigning to the perf_counter_attr struct:

struct perf_counter_attr pca;
...
struct perf_counter_attr_feature feature;

...
pca.ext_attrs = (struct perf_counter_attr_ext *)&feature;
-or-
pca.ext_attrs = &feature.head; /* secretly know that there's data that lies past 
the attr struct header */

Am I understanding this correctly?

- Corey

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