udp: Pre-populate msg_names with local address

udp_splice_namebuf is now used only for spliced sending, and so it is
only ever populated with the localhost address, either IPv4 or IPv6.
So, replace the awkward initialization in udp_sock_handler_splice()
with statically initialized versions for IPv4 and IPv6.  We then just
need to update the port number in udp_sock_handler_splice().

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 25 insertions, 22 deletions

diff --git a/udp.c b/udp.c
index 6951c4c..f6c07a5 100644
--- a/udp.c
+++ b/udp.c
@@ -232,11 +232,18 @@ static struct mmsghdr	udp4_l2_mh_tap		[UDP_MAX_FRAMES];
 static struct mmsghdr	udp6_l2_mh_tap		[UDP_MAX_FRAMES];
 
 /* recvmmsg()/sendmmsg() data for "spliced" connections */
-static struct sockaddr_storage udp_splice_namebuf;
-
 static struct iovec	udp4_iov_splice		[UDP_MAX_FRAMES];
 static struct iovec	udp6_iov_splice		[UDP_MAX_FRAMES];
 
+static struct sockaddr_in udp4_localname = {
+	.sin_family = AF_INET,
+	.sin_addr = IN4ADDR_LOOPBACK_INIT,
+};
+static struct sockaddr_in6 udp6_localname = {
+	.sin6_family = AF_INET6,
+	.sin6_addr = IN6ADDR_LOOPBACK_INIT,
+};
+
 static struct mmsghdr	udp4_mh_splice		[UDP_MAX_FRAMES];
 static struct mmsghdr	udp6_mh_splice		[UDP_MAX_FRAMES];
 
@@ -610,23 +617,10 @@ static void udp_sock_handler_splice(const struct ctx *c, union epoll_ref ref,
 	if (n <= 0)
 		return;
 
-	if (v6) {
-		*((struct sockaddr_in6 *)&udp_splice_namebuf) =
-		 ((struct sockaddr_in6) {
-			.sin6_family = AF_INET6,
-			.sin6_addr = IN6ADDR_LOOPBACK_INIT,
-			.sin6_port = htons(dst),
-			.sin6_scope_id = 0,
-		});
-	} else {
-		*((struct sockaddr_in *)&udp_splice_namebuf) =
-		 ((struct sockaddr_in) {
-			.sin_family = AF_INET,
-			.sin_addr = { .s_addr = htonl(INADDR_LOOPBACK) },
-			.sin_port = htons(dst),
-			.sin_zero = { 0 },
-		});
-	}
+	if (v6)
+		udp6_localname.sin6_port = htons(dst);
+	else
+		udp4_localname.sin_port = htons(dst);
 
 	for (i = 0; i < n; i += m) {
 		in_port_t src = sa_port(v6, mmh_recv[i].msg_hdr.msg_name);
@@ -1256,9 +1250,11 @@ static void udp_splice_iov_init(void)
 		struct msghdr *mh4 = &udp4_mh_splice[i].msg_hdr;
 		struct msghdr *mh6 = &udp6_mh_splice[i].msg_hdr;
 
-		mh4->msg_name = mh6->msg_name = &udp_splice_namebuf;
-		mh4->msg_namelen = sizeof(udp_splice_namebuf);
-		mh6->msg_namelen = sizeof(udp_splice_namebuf);
+		mh4->msg_name = &udp4_localname;
+		mh4->msg_namelen = sizeof(udp4_localname);
+
+		mh6->msg_name = &udp6_localname;
+		mh6->msg_namelen = sizeof(udp6_localname);
 
 		udp4_iov_splice[i].iov_base = udp4_l2_buf[i].data;
 		udp6_iov_splice[i].iov_base = udp6_l2_buf[i].data;
diff --git a/util.h b/util.h
index 02b55a9..3baec91 100644
--- a/util.h
+++ b/util.h
@@ -79,6 +79,13 @@
 	(IN_MULTICAST(ntohl((a)->s_addr)))
 #define IN4_ARE_ADDR_EQUAL(a, b) \
 	(((struct in_addr *)(a))->s_addr == ((struct in_addr *)b)->s_addr)
+#if __BYTE_ORDER == __BIG_ENDIAN
+#define IN4ADDR_LOOPBACK_INIT \
+	{ .s_addr	= INADDR_LOOPBACK }
+#else
+#define IN4ADDR_LOOPBACK_INIT \
+	{ .s_addr	= __bswap_constant_32(INADDR_LOOPBACK) }
+#endif
 
 #define NS_FN_STACK_SIZE	(RLIMIT_STACK_VAL * 1024 / 8)
 int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size, int flags,