udp: Don't pre-initialize msghdr array

In udp_tap_handler() the array of msghdr structures, mm[], is initialized
to zero.  Since UIO_MAXIOV is 1024, this can be quite a large zero, which
is expensive if we only end up using a few of its entries.  It also makes
it less obvious how we're setting all the control fields at the point we
actually invoke sendmmsg().

Rather than pre-initializing it, just initialize each element as we use it.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 5 insertions, 1 deletions

diff --git a/udp.c b/udp.c
index c4ebecc..864e7b2 100644
--- a/udp.c
+++ b/udp.c
@@ -968,7 +968,7 @@ void udp_sock_handler(const struct ctx *c, union epoll_ref ref, uint32_t events,
 int udp_tap_handler(struct ctx *c, int af, const void *addr,
 		    const struct pool *p, const struct timespec *now)
 {
-	struct mmsghdr mm[UIO_MAXIOV] = { 0 };
+	struct mmsghdr mm[UIO_MAXIOV];
 	struct iovec m[UIO_MAXIOV];
 	struct sockaddr_in6 s_in6;
 	struct sockaddr_in s_in;
@@ -1087,6 +1087,10 @@ int udp_tap_handler(struct ctx *c, int af, const void *addr,
 		mm[i].msg_hdr.msg_iov = m + i;
 		mm[i].msg_hdr.msg_iovlen = 1;
 
+		mm[i].msg_hdr.msg_control = NULL;
+		mm[i].msg_hdr.msg_controllen = 0;
+		mm[i].msg_hdr.msg_flags = 0;
+
 		count++;
 	}