net: implement a SO_DOMAIN getsockoption

This sockopt goes in line with SO_TYPE and SO_PROTOCOL. It makes it
possible for userspace programs to pass around file descriptors — I
am referring to arguments-to-functions, but it may even work for the
fd passing over UNIX sockets — without needing to also pass the
auxiliary information (PF_INET6/IPPROTO_TCP).
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/alpha/include/asm/socket.h

@@ -33,6 +33,7 @@
 #define	SO_SNDTIMEO	0x1013
 #define SO_ACCEPTCONN	0x1014
 #define SO_PROTOCOL	0x1028
+#define SO_DOMAIN	0x1029
 
 /* linux-specific, might as well be the same as on i386 */
 #define SO_NO_CHECK	11

arch/arm/include/asm/socket.h

@@ -58,5 +58,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_SOCKET_H */

arch/avr32/include/asm/socket.h

@@ -58,5 +58,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* __ASM_AVR32_SOCKET_H */

arch/cris/include/asm/socket.h

@@ -60,6 +60,7 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_SOCKET_H */
 

arch/frv/include/asm/socket.h

@@ -58,6 +58,7 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_SOCKET_H */
 

arch/h8300/include/asm/socket.h

@@ -58,5 +58,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_SOCKET_H */

arch/ia64/include/asm/socket.h

@@ -67,5 +67,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_IA64_SOCKET_H */

arch/m32r/include/asm/socket.h

@@ -58,5 +58,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_M32R_SOCKET_H */

arch/m68k/include/asm/socket.h

@@ -58,5 +58,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_SOCKET_H */

arch/microblaze/include/asm/socket.h

@@ -67,5 +67,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_MICROBLAZE_SOCKET_H */

arch/mips/include/asm/socket.h

@@ -43,6 +43,7 @@ To add: #define SO_REUSEPORT 0x0200	/* Allow local address and port reuse.  */
 #define SO_RCVTIMEO 	0x1006	/* receive timeout */
 #define SO_ACCEPTCONN	0x1009
 #define SO_PROTOCOL	0x1028	/* protocol type */
+#define SO_DOMAIN	0x1029	/* domain/socket family */
 
 /* linux-specific, might as well be the same as on i386 */
 #define SO_NO_CHECK	11

arch/mn10300/include/asm/socket.h

@@ -58,5 +58,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_SOCKET_H */

arch/parisc/include/asm/socket.h

@@ -25,6 +25,7 @@
 #define SO_ERROR	0x1007
 #define SO_TYPE		0x1008
 #define SO_PROTOCOL	0x1028
+#define SO_DOMAIN	0x1029
 #define SO_PEERNAME	0x2000
 
 #define SO_NO_CHECK	0x400b

arch/powerpc/include/asm/socket.h

@@ -65,5 +65,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif	/* _ASM_POWERPC_SOCKET_H */

arch/s390/include/asm/socket.h

@@ -66,5 +66,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_SOCKET_H */

arch/sparc/include/asm/socket.h

@@ -30,6 +30,7 @@
 #define SO_ERROR	0x1007
 #define SO_TYPE		0x1008
 #define SO_PROTOCOL	0x1028
+#define SO_DOMAIN	0x1029
 
 
 /* Linux specific, keep the same. */

arch/x86/include/asm/socket.h

@@ -58,5 +58,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* _ASM_X86_SOCKET_H */

arch/xtensa/include/asm/socket.h

@@ -69,5 +69,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif	/* _XTENSA_SOCKET_H */

include/asm-generic/socket.h

@@ -61,5 +61,6 @@
 #define SCM_TIMESTAMPING	SO_TIMESTAMPING
 
 #define SO_PROTOCOL		38
+#define SO_DOMAIN		39
 
 #endif /* __ASM_GENERIC_SOCKET_H */

net/core/sock.c

@@ -483,6 +483,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
 		break;
 	case SO_TYPE:
 	case SO_PROTOCOL:
+	case SO_DOMAIN:
 	case SO_ERROR:
 		ret = -ENOPROTOOPT;
 		break;
@@ -769,6 +770,10 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
 		v.val = sk->sk_protocol;
 		break;
 
+	case SO_DOMAIN:
+		v.val = sk->sk_family;
+		break;
+
 	case SO_ERROR:
 		v.val = -sock_error(sk);
 		if (v.val == 0)