Re: [PATCH] perf_counter: extensible perf_counter_attr

Corey Ashford
2009-06-08T21:18:27Z

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@chello.nl>
>>> ---
>>> 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