net: Facility to report route quality of connected sockets

This patch add the SO_CNX_ADVICE socket option (setsockopt only). The
purpose is to allow an application to give feedback to the kernel about
the quality of the network path for a connected socket. The value
argument indicates the type of quality report. For this initial patch
the only supported advice is a value of 1 which indicates "bad path,
please reroute"-- the action taken by the kernel is to call
dst_negative_advice which will attempt to choose a different ECMP route,
reset the TX hash for flow label and UDP source port in encapsulation,
etc.

This facility should be useful for connected UDP sockets where only the
application can provide any feedback about path quality. It could also
be useful for TCP applications that have additional knowledge about the
path outside of the normal TCP control loop.

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/alpha/include/uapi/asm/socket.h

@@ -95,4 +95,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif /* _UAPI_ASM_SOCKET_H */

arch/avr32/include/uapi/asm/socket.h

@@ -88,4 +88,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif /* _UAPI__ASM_AVR32_SOCKET_H */

arch/frv/include/uapi/asm/socket.h

@@ -88,5 +88,7 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif /* _ASM_SOCKET_H */
 

arch/ia64/include/uapi/asm/socket.h

@@ -97,4 +97,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif /* _ASM_IA64_SOCKET_H */

arch/m32r/include/uapi/asm/socket.h

@@ -88,4 +88,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif /* _ASM_M32R_SOCKET_H */

arch/mips/include/uapi/asm/socket.h

@@ -106,4 +106,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif /* _UAPI_ASM_SOCKET_H */

arch/mn10300/include/uapi/asm/socket.h

@@ -88,4 +88,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif /* _ASM_SOCKET_H */

arch/parisc/include/uapi/asm/socket.h

@@ -87,4 +87,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	0x402C
 #define SO_ATTACH_REUSEPORT_EBPF	0x402D
 
+#define SO_CNX_ADVICE		0x402E
+
 #endif /* _UAPI_ASM_SOCKET_H */

arch/powerpc/include/uapi/asm/socket.h

@@ -95,4 +95,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif	/* _ASM_POWERPC_SOCKET_H */

arch/s390/include/uapi/asm/socket.h

@@ -94,4 +94,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif /* _ASM_SOCKET_H */

arch/sparc/include/uapi/asm/socket.h

@@ -84,6 +84,8 @@
 #define SO_ATTACH_REUSEPORT_CBPF	0x0035
 #define SO_ATTACH_REUSEPORT_EBPF	0x0036
 
+#define SO_CNX_ADVICE		0x0037
+
 /* Security levels - as per NRL IPv6 - don't actually do anything */
 #define SO_SECURITY_AUTHENTICATION		0x5001
 #define SO_SECURITY_ENCRYPTION_TRANSPORT	0x5002

arch/xtensa/include/uapi/asm/socket.h

@@ -99,4 +99,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif	/* _XTENSA_SOCKET_H */

include/uapi/asm-generic/socket.h

@@ -90,4 +90,6 @@
 #define SO_ATTACH_REUSEPORT_CBPF	51
 #define SO_ATTACH_REUSEPORT_EBPF	52
 
+#define SO_CNX_ADVICE		53
+
 #endif /* __ASM_GENERIC_SOCKET_H */

net/core/sock.c

@@ -987,6 +987,10 @@ set_rcvbuf:
 		sk->sk_incoming_cpu = val;
 		break;
 
+	case SO_CNX_ADVICE:
+		if (val == 1)
+			dst_negative_advice(sk);
+		break;
 	default:
 		ret = -ENOPROTOOPT;
 		break;