perf: Rework/fix the whole read vs group stuff

Replace PERF_SAMPLE_GROUP with PERF_SAMPLE_READ and introduce
PERF_FORMAT_GROUP to deal with group reads in a more generic
way.

This allows you to get group reads out of read() as well.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Corey J Ashford <cjashfor@us.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: stephane eranian <eranian@googlemail.com>
LKML-Reference: <20090813103655.117411814@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/perf_counter.h

@@ -115,7 +115,7 @@ enum perf_counter_sample_format {
 	PERF_SAMPLE_TID				= 1U << 1,
 	PERF_SAMPLE_TIME			= 1U << 2,
 	PERF_SAMPLE_ADDR			= 1U << 3,
-	PERF_SAMPLE_GROUP			= 1U << 4,
+	PERF_SAMPLE_READ			= 1U << 4,
 	PERF_SAMPLE_CALLCHAIN			= 1U << 5,
 	PERF_SAMPLE_ID				= 1U << 6,
 	PERF_SAMPLE_CPU				= 1U << 7,
@@ -127,16 +127,32 @@ enum perf_counter_sample_format {
 };
 
 /*
- * Bits that can be set in attr.read_format to request that
- * reads on the counter should return the indicated quantities,
- * in increasing order of bit value, after the counter value.
+ * The format of the data returned by read() on a perf counter fd,
+ * as specified by attr.read_format:
+ *
+ * struct read_format {
+ * 	{ u64		value;
+ * 	  { u64		time_enabled; } && PERF_FORMAT_ENABLED
+ * 	  { u64		time_running; } && PERF_FORMAT_RUNNING
+ * 	  { u64		id;           } && PERF_FORMAT_ID
+ * 	} && !PERF_FORMAT_GROUP
+ *
+ * 	{ u64		nr;
+ * 	  { u64		time_enabled; } && PERF_FORMAT_ENABLED
+ * 	  { u64		time_running; } && PERF_FORMAT_RUNNING
+ * 	  { u64		value;
+ * 	    { u64	id;           } && PERF_FORMAT_ID
+ * 	  }		cntr[nr];
+ * 	} && PERF_FORMAT_GROUP
+ * };
  */
 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_GROUP			= 1U << 3,
 
-	PERF_FORMAT_MAX = 1U << 3, 		/* non-ABI */
+	PERF_FORMAT_MAX = 1U << 4, 		/* non-ABI */
 };
 
 #define PERF_ATTR_SIZE_VER0	64	/* sizeof first published struct */
@@ -343,10 +359,8 @@ enum perf_event_type {
 	 * struct {
 	 * 	struct perf_event_header	header;
 	 * 	u32				pid, tid;
-	 * 	u64				value;
-	 * 	{ u64		time_enabled; 	} && PERF_FORMAT_ENABLED
-	 * 	{ u64		time_running; 	} && PERF_FORMAT_RUNNING
-	 * 	{ u64		parent_id;	} && PERF_FORMAT_ID
+	 *
+	 * 	struct read_format		values;
 	 * };
 	 */
 	PERF_EVENT_READ			= 8,
@@ -364,11 +378,22 @@ enum perf_event_type {
 	 *	{ u32			cpu, res; } && PERF_SAMPLE_CPU
 	 * 	{ u64			period;   } && PERF_SAMPLE_PERIOD
 	 *
-	 *	{ u64			nr;
-	 *	  { u64 id, val; }	cnt[nr];  } && PERF_SAMPLE_GROUP
+	 *	{ struct read_format	values;	  } && PERF_SAMPLE_READ
 	 *
 	 *	{ u64			nr,
 	 *	  u64			ips[nr];  } && PERF_SAMPLE_CALLCHAIN
+	 *
+	 * 	#
+	 * 	# The RAW record below is opaque data wrt the ABI
+	 * 	#
+	 * 	# That is, the ABI doesn't make any promises wrt to
+	 * 	# the stability of its content, it may vary depending
+	 * 	# on event, hardware, kernel version and phase of
+	 * 	# the moon.
+	 * 	#
+	 * 	# In other words, PERF_SAMPLE_RAW contents are not an ABI.
+	 * 	#
+	 *
 	 *	{ u32			size;
 	 *	  char                  data[size];}&& PERF_SAMPLE_RAW
 	 * };