unix_diag: Unix peer inode NLA

Report the peer socket inode ID as NLA. With this it's finally
possible to find out the other end of an interesting unix connection.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/unix_diag.h b/include/linux/unix_diag.h
index 3e53adb..2d74a86 100644
--- a/include/linux/unix_diag.h
+++ b/include/linux/unix_diag.h
@@ -13,6 +13,7 @@
 
 #define UDIAG_SHOW_NAME		0x00000001	/* show name (not path) */
 #define UDIAG_SHOW_VFS		0x00000002	/* show VFS inode info */
+#define UDIAG_SHOW_PEER		0x00000004	/* show peer socket info */
 
 struct unix_diag_msg {
 	__u8	udiag_family;
@@ -27,6 +28,7 @@
 enum {
 	UNIX_DIAG_NAME,
 	UNIX_DIAG_VFS,
+	UNIX_DIAG_PEER,
 
 	UNIX_DIAG_MAX,
 };