[PATCH v3 2/3] perf: Reveal PMU type in fdinfo

[Chun-Tse Shao <ctshao@google.com>]

It gives useful info on knowing which PMUs are reserved by this process.
Also add config which would be useful.
Testing cycles:

  $ ./perf stat -e cycles &
  $ cat /proc/`pidof perf`/fdinfo/3
  pos:    0
  flags:  02000002
  mnt_id: 16
  ino:    3081
  perf_event_attr.type:   0
  perf_event_attr.config: 0

Testing L1-dcache-load-misses:

  $ ./perf stat -e L1-dcache-load-misses &
  $ cat /proc/`pidof perf`/fdinfo/3
  pos:    0
  flags:  02000002
  mnt_id: 16
  ino:    1072
  perf_event_attr.type:   3
  perf_event_attr.config: 65536

Signed-off-by: Chun-Tse Shao <ctshao@google.com>
Change-Id: Ibea5618aaf00bae6f48a9b2a6e7798ab2b7f23ce
---
 kernel/events/core.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index cdd09769e6c56..398cac8b208b9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -55,6 +55,7 @@
 #include <linux/pgtable.h>
 #include <linux/buildid.h>
 #include <linux/task_work.h>
+#include <linux/seq_file.h>
 
 #include "internal.h"
 
@@ -6820,6 +6821,14 @@ static int perf_fasync(int fd, struct file *filp, int on)
 	return 0;
 }
 
+static void perf_show_fdinfo(struct seq_file *m, struct file *f)
+{
+	struct perf_event *event = f->private_data;
+
+	seq_printf(m, "perf_event_attr.type:\t%u\n", event->orig_type);
+	seq_printf(m, "perf_event_attr.config:\t%llu\n", (unsigned long long)event->attr.config);
+}
+
 static const struct file_operations perf_fops = {
 	.release		= perf_release,
 	.read			= perf_read,
@@ -6828,6 +6837,7 @@ static const struct file_operations perf_fops = {
 	.compat_ioctl		= perf_compat_ioctl,
 	.mmap			= perf_mmap,
 	.fasync			= perf_fasync,
+	.show_fdinfo		= perf_show_fdinfo,
 };
 
 /*
-- 
2.47.0.199.ga7371fff76-goog