[PATCH 03/21] perf_events: Add a helper to search for an event in a context

[Borislav Petkov <bp@amd64.org>]

From: Borislav Petkov <borislav.petkov@amd.com>

This is a straignt-forward helper to look for, e.g. already allocated
and enabled events (think persistent events here).

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
---
 kernel/perf_event.c |   21 +++++++++++++++++++++
 1 files changed, 21 insertions(+), 0 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 40478af..168764b 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -307,6 +307,27 @@ list_add_event(struct perf_event *event, struct perf_event_context *ctx)
 		ctx->nr_stat++;
 }
 
+/*
+ * Find an event in a context.
+ * Must be called with ctx->mutex and ctx->lock held.
+ */
+static struct perf_event *find_event_in_context(struct perf_event_attr *attr,
+						struct perf_event_context *ctx)
+{
+	struct perf_event *event;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
+		if (event->attr.config == attr->config) {
+			rcu_read_unlock();
+			return event;
+		}
+	}
+	rcu_read_unlock();
+
+	return NULL;
+}
+
 static void perf_group_attach(struct perf_event *event)
 {
 	struct perf_event *group_leader = event->group_leader;
-- 
1.7.1