Re: [PATCH] perf_counter: extensible perf_counter_attr

From: Corey Ashford
Date: Mon Jun 08 2009 - 17:18:31 EST

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;
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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