[PATCH RFC 3/5] perf: Add namespaces to the sideband ioctl

[Adrian Hunter <adrian.hunter@intel.com>]

Support the case of output to an active event, and return an error if
output is not possible in that case. Set PERF_RECORD_MISC_STATUS_ONLY to
differentiate the ioctl status-only sideband event from a "real" sideband
event.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 kernel/events/core.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4e76596d3bfb..ed4af231853a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8364,8 +8364,7 @@ static int perf_event_namespaces_match(struct perf_event *event)
 	return event->attr.namespaces;
 }
 
-static void perf_event_namespaces_output(struct perf_event *event,
-					 void *data)
+static int perf_event_namespaces_output(struct perf_event *event, void *data)
 {
 	struct perf_namespaces_event *namespaces_event = data;
 	struct perf_output_handle handle;
@@ -8374,7 +8373,7 @@ static void perf_event_namespaces_output(struct perf_event *event,
 	int ret;
 
 	if (!perf_event_namespaces_match(event))
-		return;
+		return -ENOENT;
 
 	perf_event_header__init_id(&namespaces_event->event_id.header,
 				   &sample, event);
@@ -8395,6 +8394,7 @@ static void perf_event_namespaces_output(struct perf_event *event,
 	perf_output_end(&handle);
 out:
 	namespaces_event->event_id.header.size = header_size;
+	return ret;
 }
 
 static void perf_fill_ns_link_info(struct perf_ns_link_info *ns_link_info,
@@ -8414,20 +8414,20 @@ static void perf_fill_ns_link_info(struct perf_ns_link_info *ns_link_info,
 	}
 }
 
-void perf_event_namespaces(struct task_struct *task)
+static int __perf_event_namespaces(struct task_struct *task, struct perf_event *event)
 {
 	struct perf_namespaces_event namespaces_event;
 	struct perf_ns_link_info *ns_link_info;
 
 	if (!atomic_read(&nr_namespaces_events))
-		return;
+		return -ENOENT;
 
 	namespaces_event = (struct perf_namespaces_event){
 		.task	= task,
 		.event_id  = {
 			.header = {
 				.type = PERF_RECORD_NAMESPACES,
-				.misc = 0,
+				.misc = event ? PERF_RECORD_MISC_STATUS_ONLY : 0,
 				.size = sizeof(namespaces_event.event_id),
 			},
 			/* .pid */
@@ -8467,9 +8467,12 @@ void perf_event_namespaces(struct task_struct *task)
 			       task, &cgroupns_operations);
 #endif
 
-	perf_iterate_sb(perf_event_namespaces_output,
-			&namespaces_event,
-			NULL);
+	return perf_output_sb(perf_event_namespaces_output, &namespaces_event, NULL, event);
+}
+
+void perf_event_namespaces(struct task_struct *task)
+{
+	__perf_event_namespaces(task, NULL);
 }
 
 /*
@@ -12880,7 +12883,10 @@ static int perf_event_emit_fork(struct perf_event *event, struct task_struct *ta
 
 static int perf_event_emit_namespaces(struct perf_event *event, struct task_struct *task)
 {
-	return -EINVAL;
+	if (!event->attr.namespaces)
+		return -EINVAL;
+
+	return __perf_event_namespaces(task, event);
 }
 
 static int perf_event_emit_comm(struct perf_event *event, struct task_struct *task)
-- 
2.34.1