[PATCH 2/3] perf tools: Update ioctl documentation for PERF_IOC_FLAG_GROUP

[Namhyung Kim]

The ioctl interface of perf event fd receives 3 arguments
to control event group behavior but it lacked documentation.

Signed-off-by: Namhyung Kim <namhyung.kim@xxxxxxx>
---
 tools/perf/design.txt |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tools/perf/design.txt b/tools/perf/design.txt
index bd0bb1b1279b..67e5d0cace85 100644
--- a/tools/perf/design.txt
+++ b/tools/perf/design.txt
@@ -409,14 +409,15 @@ Counters can be enabled and disabled in two ways: via ioctl and via
 prctl.  When a counter is disabled, it doesn't count or generate
 events but does continue to exist and maintain its count value.
 
-An individual counter or counter group can be enabled with
+An individual counter can be enabled with
 
-	ioctl(fd, PERF_EVENT_IOC_ENABLE);
+	ioctl(fd, PERF_EVENT_IOC_ENABLE, 0);
 
 or disabled with
 
-	ioctl(fd, PERF_EVENT_IOC_DISABLE);
+	ioctl(fd, PERF_EVENT_IOC_DISABLE, 0);
 
+For a counter group, pass PERF_IOC_FLAG_GROUP as the third argument.
 Enabling or disabling the leader of a group enables or disables the
 whole group; that is, while the group leader is disabled, none of the
 counters in the group will count.  Enabling or disabling a member of a
-- 
1.7.10.2

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