[PATCH] knfsd: Fix cmsg setup for sock_sendmsg in svc_sendto

From: Trond Myklebust <trond.myklebust@fys.uio.no>

... see the code in ip_sockglue.c + the macros in socket.h....
AFAICS the control messages have wierd alignment requirements.

net/sunrpc/svcsock.c

@@ -352,9 +352,9 @@ svc_sendto(struct svc_rqst *rqstp, struct xdr_buf *xdr)
 	struct svc_sock	*svsk = rqstp->rq_sock;
 	struct socket	*sock = svsk->sk_sock;
 	int		slen;
-	struct { struct cmsghdr cmh;
-		struct in_pktinfo pki;
-	} cm;
+	char 		buffer[CMSG_SPACE(sizeof(struct in_pktinfo))];
+	struct cmsghdr *cmh = (struct cmsghdr *)buffer;
+	struct in_pktinfo *pki = (struct in_pktinfo *)CMSG_DATA(cmh);
 	int		len = 0;
 	int		result;
 	int		size;
@@ -374,13 +374,13 @@ svc_sendto(struct svc_rqst *rqstp, struct xdr_buf *xdr)
 		msg.msg_iovlen  = 0;
 		msg.msg_flags	= MSG_MORE;
 
-		msg.msg_control = &cm;
-		msg.msg_controllen = sizeof(cm);
-		cm.cmh.cmsg_len = sizeof(cm);
-		cm.cmh.cmsg_level = SOL_IP;
-		cm.cmh.cmsg_type = IP_PKTINFO;
-		cm.pki.ipi_ifindex = 0;
-		cm.pki.ipi_spec_dst.s_addr = rqstp->rq_daddr;
+		msg.msg_control = cmh;
+		msg.msg_controllen = sizeof(buffer);
+		cmh->cmsg_len = CMSG_LEN(sizeof(*pki));
+		cmh->cmsg_level = SOL_IP;
+		cmh->cmsg_type = IP_PKTINFO;
+		pki->ipi_ifindex = 0;
+		pki->ipi_spec_dst.s_addr = rqstp->rq_daddr;
 
 		if (sock_sendmsg(sock, &msg, 0) < 0)
 			goto out;