Re: [PATCH] perf_counter: extensible perf_counter_attr

Ingo Molnar
2009-06-08T21:50:39Z

* Corey Ashford <cjashfor@linux.vnet.ibm.com> wrote:

> Peter Zijlstra wrote:
>> On Mon, 2009-06-08 at 14:18 -0700, Corey Ashford wrote:
>>> pca.ext_attrs = &feature.head; /* secretly know that there's data
>>> that lies past the attr struct header */
>>
>> Right, except its not so very secret since we have the type field
>> telling us.
>
> I see. Thanks for the explanation. Looks like a good plan to me!

i think we'd have a much simpler implementation by changing
__reserved_1 to attr_size. When the kernel adds new attributes, the
size will increase - old user-space will use the old size which the
kernel detects and adopts to (by zeroing out that attribute space).

That way we'll always have a nice flat attributes structure, with no
quirky chaining that has field-dependent data types ...

Ingo