unix: add AF_IUCV and SockaddrIUCV

On z series machines the IUCV address family is used to communicate
between parts of the machine and other VMs that may be running.

This adds support for addressing these services using AF_IUCV.

Fixes golang/go#40826

Change-Id: I3aba3beb5cb98d9c548d7abc874ca86fb25c8a52
GitHub-Last-Rev: b964d186b45dd907f4ae302ea9b1ff63e3592eb6
GitHub-Pull-Request: golang/sys#76
Reviewed-on: https://go-review.googlesource.com/c/sys/+/248777
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/syscall_linux.go

@@ -885,6 +885,32 @@ func (sa *SockaddrL2TPIP6) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	return unsafe.Pointer(&sa.raw), SizeofSockaddrL2TPIP6, nil
 }
 
+// SockaddrIUCV implements the Sockaddr interface for AF_IUCV sockets.
+type SockaddrIUCV struct {
+	UserID string
+	Name   string
+	raw    RawSockaddrIUCV
+}
+
+func (sa *SockaddrIUCV) sockaddr() (unsafe.Pointer, _Socklen, error) {
+	sa.raw.Family = AF_IUCV
+	// These are EBCDIC encoded by the kernel, but we still need to pad them
+	// with blanks. Initializing with blanks allows the caller to feed in either
+	// a padded or an unpadded string.
+	for i := 0; i < 8; i++ {
+		sa.raw.Nodeid[i] = ' '
+		sa.raw.User_id[i] = ' '
+		sa.raw.Name[i] = ' '
+	}
+	for i, b := range []byte(sa.UserID[:8]) {
+		sa.raw.User_id[i] = int8(b)
+	}
+	for i, b := range []byte(sa.Name[:8]) {
+		sa.raw.Name[i] = int8(b)
+	}
+	return unsafe.Pointer(&sa.raw), SizeofSockaddrIUCV, nil
+}
+
 func anyToSockaddr(fd int, rsa *RawSockaddrAny) (Sockaddr, error) {
 	switch rsa.Addr.Family {
 	case AF_NETLINK:
@@ -1065,6 +1091,23 @@ func anyToSockaddr(fd int, rsa *RawSockaddrAny) (Sockaddr, error) {
 		}
 
 		return sa, nil
+	case AF_IUCV:
+		pp := (*RawSockaddrIUCV)(unsafe.Pointer(rsa))
+
+		var user [8]byte
+		var name [8]byte
+
+		for i := 0; i < 8; i++ {
+			user[i] = byte(pp.User_id[i])
+			name[i] = byte(pp.Name[i])
+		}
+
+		sa := &SockaddrIUCV{
+			UserID: string(user[:]),
+			Name:   string(name[:]),
+		}
+		return sa, nil
+
 	}
 	return nil, EAFNOSUPPORT
 }