userns: Convert drm to use kuid and kgid and struct pid where appropriate

Blink Blink this had not been converted to use struct pid ages ago?

- On drm open capture the openers kuid and struct pid.
- On drm close release the kuid and struct pid
- When reporting the uid and pid convert the kuid and struct pid
  into values in the appropriate namespace.

Cc: dri-devel@lists.freedesktop.org
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

drivers/gpu/drm/drm_ioctl.c

@@ -215,8 +215,8 @@ int drm_getclient(struct drm_device *dev, void *data,
 	list_for_each_entry(pt, &dev->filelist, lhead) {
 		if (i++ >= idx) {
 			client->auth = pt->authenticated;
-			client->pid = pt->pid;
-			client->uid = pt->uid;
+			client->pid = pid_vnr(pt->pid);
+			client->uid = from_kuid_munged(current_user_ns(), pt->uid);
 			client->magic = pt->magic;
 			client->iocs = pt->ioctl_count;
 			mutex_unlock(&dev->struct_mutex);