perf_counter: Add forward/backward attribute ABI compatibility

Provide for means of extending the perf_counter_attr in a 'natural' way.

We allow growing the structure by appending fields at the end by specifying
the full structure size inside it.

When a new kernel sees a smaller (old) structure, it will 0 pad the tail.
When an old kernel sees a larger (new) structure, it will verify the tail
consists of 0s, otherwise fail.

If we fail due to a size-mismatch, we return -E2BIG and write the kernel's
native attribe size back into the provided structure.

Furthermore, add some attribute verification, so that we'll fail counter
creation when unknown bits are present (PERF_SAMPLE, PERF_FORMAT, or in
the __reserved fields).

(This ABI detail is introduced while keeping the existing syscall ABI.)

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 4 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 7c4f32f6ae1a..1b3118a1023a 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -120,6 +120,8 @@ enum perf_counter_sample_format {
         PERF_SAMPLE_ID                          = 1U << 6,
         PERF_SAMPLE_CPU                         = 1U << 7,
         PERF_SAMPLE_PERIOD                      = 1U << 8,
+
+        PERF_SAMPLE_MAX = 1U << 9,              /* non-ABI */
 };
 
 /*
@@ -131,17 +133,26 @@ enum perf_counter_read_format {
         PERF_FORMAT_TOTAL_TIME_ENABLED          = 1U << 0,
         PERF_FORMAT_TOTAL_TIME_RUNNING          = 1U << 1,
         PERF_FORMAT_ID                          = 1U << 2,
+
+        PERF_FORMAT_MAX = 1U << 3,              /* non-ABI */
 };
 
+#define PERF_ATTR_SIZE_VER0     64      /* sizeof first published struct */
+
 /*
  * Hardware event to monitor via a performance monitoring counter:
  */
 struct perf_counter_attr {
+
         /*
          * Major type: hardware/software/tracepoint/etc.
          */
         __u32                   type;
-        __u32                   __reserved_1;
+
+        /*
+         * Size of the attr structure, for fwd/bwd compat.
+         */
+        __u32                   size;
 
         /*
          * Type specific configuration information.
@@ -168,12 +179,12 @@ struct perf_counter_attr {
                                 comm           :  1, /* include comm data     */
                                 freq           :  1, /* use freq, not period  */
 
-                                __reserved_2   : 53;
+                                __reserved_1   : 53;
 
         __u32                   wakeup_events;  /* wakeup every n events */
-        __u32                   __reserved_3;
+        __u32                   __reserved_2;
 
-        __u64                   __reserved_4;
+        __u64                   __reserved_3;
 };
 
 /*