[PATCH RFC 4/5] perf: Add comm 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 | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index ed4af231853a..cddc02c2e411 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8265,8 +8265,7 @@ static int perf_event_comm_match(struct perf_event *event)
 	return event->attr.comm;
 }
 
-static void perf_event_comm_output(struct perf_event *event,
-				   void *data)
+static int perf_event_comm_output(struct perf_event *event, void *data)
 {
 	struct perf_comm_event *comm_event = data;
 	struct perf_output_handle handle;
@@ -8275,7 +8274,7 @@ static void perf_event_comm_output(struct perf_event *event,
 	int ret;
 
 	if (!perf_event_comm_match(event))
-		return;
+		return -ENOENT;
 
 	perf_event_header__init_id(&comm_event->event_id.header, &sample, event);
 	ret = perf_output_begin(&handle, &sample, event,
@@ -8296,9 +8295,10 @@ static void perf_event_comm_output(struct perf_event *event,
 	perf_output_end(&handle);
 out:
 	comm_event->event_id.header.size = size;
+	return ret;
 }
 
-static void perf_event_comm_event(struct perf_comm_event *comm_event)
+static int perf_event_comm_event(struct perf_comm_event *comm_event, struct perf_event *event)
 {
 	char comm[TASK_COMM_LEN];
 	unsigned int size;
@@ -8312,17 +8312,15 @@ static void perf_event_comm_event(struct perf_comm_event *comm_event)
 
 	comm_event->event_id.header.size = sizeof(comm_event->event_id) + size;
 
-	perf_iterate_sb(perf_event_comm_output,
-		       comm_event,
-		       NULL);
+	return perf_output_sb(perf_event_comm_output, comm_event, NULL, event);
 }
 
-void perf_event_comm(struct task_struct *task, bool exec)
+static int __perf_event_comm(struct task_struct *task, bool exec, struct perf_event *event)
 {
 	struct perf_comm_event comm_event;
 
 	if (!atomic_read(&nr_comm_events))
-		return;
+		return -ENOENT;
 
 	comm_event = (struct perf_comm_event){
 		.task	= task,
@@ -8331,7 +8329,8 @@ void perf_event_comm(struct task_struct *task, bool exec)
 		.event_id  = {
 			.header = {
 				.type = PERF_RECORD_COMM,
-				.misc = exec ? PERF_RECORD_MISC_COMM_EXEC : 0,
+				.misc = (exec ? PERF_RECORD_MISC_COMM_EXEC : 0) |
+					(event ? PERF_RECORD_MISC_STATUS_ONLY : 0),
 				/* .size */
 			},
 			/* .pid */
@@ -8339,7 +8338,12 @@ void perf_event_comm(struct task_struct *task, bool exec)
 		},
 	};
 
-	perf_event_comm_event(&comm_event);
+	return perf_event_comm_event(&comm_event, event);
+}
+
+void perf_event_comm(struct task_struct *task, bool exec)
+{
+	__perf_event_comm(task, exec, NULL);
 }
 
 /*
@@ -12891,7 +12895,10 @@ static int perf_event_emit_namespaces(struct perf_event *event, struct task_stru
 
 static int perf_event_emit_comm(struct perf_event *event, struct task_struct *task)
 {
-	return -EINVAL;
+	if (!event->attr.comm)
+		return -EINVAL;
+
+	return __perf_event_comm(task, false, event);
 }
 
 static int perf_event_emit_mmap(struct perf_event *event, struct task_struct *task)
-- 
2.34.1