fix abstract unix domain sockets

R=rsc
DELTA=5  (3 added, 0 deleted, 2 changed)
OCL=28845
CL=28849

src/lib/net/net_linux.go

@@ -95,6 +95,7 @@ func unixToSockaddr(name string) (sa1 *syscall.Sockaddr, err os.Error) {
 	if sa.Path[0] == '@' {
 		sa.Path[0] = 0;
 	}
+	sa.Length = 1 + int64(n) + 1;	// family, name, \0
 
 	return (*syscall.Sockaddr)(unsafe.Pointer(sa)), nil;
 }

src/lib/syscall/socket_linux.go

@@ -19,7 +19,8 @@ var SocketDisableIPv6 bool
 func saLen(s *Sockaddr) int64 {
 	switch s.Family {
 	case AF_UNIX:
-		return SizeofSockaddrUnix;
+		sa := (*SockaddrUnix)(unsafe.Pointer(s));
+		return sa.Length;
 	case AF_INET:
 		return SizeofSockaddrInet4;
 	case AF_INET6:

src/lib/syscall/types_amd64_linux.go

@@ -166,7 +166,8 @@ const (
 
 type SockaddrUnix struct {
 	Family	uint16;
-	Path	[108]byte
+	Path	[108]byte;
+	Length	int64;	// Not part of the kernel structure; used internally
 }
 const SizeofSockaddrUnix = 110