Re: [PATCH] perf_counter: extensible perf_counter_attr

Ingo Molnar
2009-06-09T06:54:19Z

* Paul Mackerras <paulus@samba.org> wrote:

> Peter Zijlstra writes:
>
> > Allow extending the perf_counter_attr structure by linking extended
> > structures to it.
>
> ...
>
> > @@ -175,6 +175,13 @@ struct perf_counter_attr {
> > __u32 __reserved_3;
> >
> > __u64 __reserved_4;
> > +
> > + struct perf_counter_attr_ext *ext_attrs;
> > +};
>
> Since this is a user-visible structure, you've just introduced an
> ABI difference between 32-bit and 64-bit processes, which we've
> managed to avoid so far. [...]

This is a good point too - handling pointers in ABIs is possible but
should be avoided as much as possible: it creates the need to
introduce a compat_sys_perf_counter_open() and doubles the syscall
table complexity.

Lets do the s/__reserved_1/attr_size ABI i suggested (i outlined
various properties of it in the previous mail). Agreed?

Ingo