[PATCH v2 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 extra attributes 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
perf_event-attr.config1:        0
perf_event-attr.config2:        0
perf_event-attr.config3:        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
perf_event-attr.config1:        0
perf_event-attr.config2:        0
perf_event-attr.config3:        0
```

Signed-off-by: Chun-Tse Shao <ctshao@google.com>
---
 kernel/events/core.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index cdd09769e6c56..c950b6fc92cda 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 +6821,17 @@ 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", event->attr.config);
+	seq_printf(m, "perf_event-attr.config1:\t%llu\n", event->attr.config1);
+	seq_printf(m, "perf_event-attr.config2:\t%llu\n", event->attr.config2);
+	seq_printf(m, "perf_event-attr.config3:\t%llu\n", event->attr.config3);
+}
+
 static const struct file_operations perf_fops = {
 	.release		= perf_release,
 	.read			= perf_read,
@@ -6828,6 +6840,7 @@ static const struct file_operations perf_fops = {
 	.compat_ioctl		= perf_compat_ioctl,
 	.mmap			= perf_mmap,
 	.fasync			= perf_fasync,
+	.show_fdinfo		= perf_show_fdinfo,
 };

 /*
--
2.47.0.163.g1226f6d8fa-goog