[PATCH] perf_counter: Always return the parent counter id to userspace

[Anton Blanchard <anton@samba.org>]

When inheriting counters new tasks get new counter ids. Since
userspace only knows about the parent ids we need to return them
and not the actual ids.

Signed-off-by: Anton Blanchard <anton@samba.org>
---

Index: linux.trees.git/kernel/perf_counter.c
===================================================================
--- linux.trees.git.orig/kernel/perf_counter.c	2009-07-20 20:17:44.000000000 +1000
+++ linux.trees.git/kernel/perf_counter.c	2009-07-20 20:36:13.000000000 +1000
@@ -154,6 +154,20 @@
 	}
 }
 
+/* 
+ * If we inherit counters we want to return the parent counter id 
+ * to userspace.
+ */
+static u64 primary_counter_id(struct perf_counter *counter)
+{
+	u64 id = counter->id;
+
+	if (counter->parent)
+		id = counter->parent->id;
+
+	return id;
+}
+
 /*
  * Get the perf_counter_context for a task and lock it.
  * This has to cope with with the fact that until it is locked,
@@ -1705,7 +1719,7 @@
 		values[n++] = counter->total_time_running +
 			atomic64_read(&counter->child_total_time_running);
 	if (counter->attr.read_format & PERF_FORMAT_ID)
-		values[n++] = counter->id;
+		values[n++] = primary_counter_id(counter);
 	mutex_unlock(&counter->child_mutex);
 
 	if (count < n * sizeof(u64))
@@ -2548,7 +2562,7 @@
 		lost_event.header.type = PERF_EVENT_LOST;
 		lost_event.header.misc = 0;
 		lost_event.header.size = sizeof(lost_event);
-		lost_event.id          = counter->id;
+		lost_event.id          = primary_counter_id(counter);
 		lost_event.lost        = atomic_xchg(&data->lost, 0);
 
 		perf_output_put(handle, lost_event);
@@ -2704,8 +2718,10 @@
 	if (sample_type & PERF_SAMPLE_ADDR)
 		perf_output_put(&handle, data->addr);
 
-	if (sample_type & PERF_SAMPLE_ID)
-		perf_output_put(&handle, counter->id);
+	if (sample_type & PERF_SAMPLE_ID) {
+		u64 id = primary_counter_id(counter);
+		perf_output_put(&handle, id);
+	}
 
 	if (sample_type & PERF_SAMPLE_CPU)
 		perf_output_put(&handle, cpu_entry);
@@ -2727,7 +2743,7 @@
 			if (sub != counter)
 				sub->pmu->read(sub);
 
-			group_entry.id = sub->id;
+			group_entry.id = primary_counter_id(sub);
 			group_entry.counter = atomic64_read(&sub->count);
 
 			perf_output_put(&handle, group_entry);
@@ -2790,11 +2806,7 @@
 		u64 id;
 
 		event.header.size += sizeof(u64);
-		if (counter->parent)
-			id = counter->parent->id;
-		else
-			id = counter->id;
-
+		id = primary_counter_id(counter);
 		event.format[i++] = id;
 	}
 
@@ -3209,7 +3221,7 @@
 			.size = sizeof(event),
 		},
 		.time = sched_clock(),
-		.id = counter->id,
+		.id = primary_counter_id(counter),
 		.period = period,
 	};
 
@@ -3241,7 +3253,7 @@
 			.size = sizeof(throttle_event),
 		},
 		.time	= sched_clock(),
-		.id	= counter->id,
+		.id	= primary_counter_id(counter),
 	};
 
 	ret = perf_output_begin(&handle, counter, sizeof(throttle_event), 1, 0);