iov: Helper macro to construct iovs covering existing variables or fields

Laurent's recent changes mean we use IO vectors much more heavily in the
TCP code.  In many of those cases, and few others around the code base,
individual iovs of these vectors are constructed to exactly cover existing
variables or fields.  We can make initializing such iovs shorter and
clearer with a macro for the purpose.

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

4 files changed, 16 insertions, 21 deletions

diff --git a/iov.h b/iov.h
index 6058af7..5668ca5 100644
--- a/iov.h
+++ b/iov.h
@@ -18,6 +18,9 @@
 #include <unistd.h>
 #include <string.h>
 
+#define IOV_OF_LVALUE(lval) \
+	(struct iovec){ .iov_base = &(lval), .iov_len = sizeof(lval) }
+
 size_t iov_skip_bytes(const struct iovec *iov, size_t n,
 		      size_t skip, size_t *offset);
 size_t iov_from_buf(const struct iovec *iov, size_t iov_cnt,
diff --git a/tap.c b/tap.c
index c6864ac..91fd2e2 100644
--- a/tap.c
+++ b/tap.c
@@ -79,8 +79,7 @@ void tap_send_single(const struct ctx *c, const void *data, size_t l2len)
 	size_t iovcnt = 0;
 
 	if (c->mode == MODE_PASST) {
-		iov[iovcnt].iov_base = &vnet_len;
-		iov[iovcnt].iov_len = sizeof(vnet_len);
+		iov[iovcnt] = IOV_OF_LVALUE(vnet_len);
 		iovcnt++;
 	}
 
diff --git a/tcp.c b/tcp.c
index d42c01d..845afce 100644
--- a/tcp.c
+++ b/tcp.c
@@ -290,6 +290,7 @@
 
 #include "checksum.h"
 #include "util.h"
+#include "iov.h"
 #include "ip.h"
 #include "passt.h"
 #include "tap.h"
@@ -954,10 +955,8 @@ static void tcp_sock4_iov_init(const struct ctx *c)
 		iov = tcp4_l2_iov[i];
 
 		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp4_payload_tap_hdr[i]);
-		iov[TCP_IOV_ETH].iov_base = &tcp4_eth_src;
-		iov[TCP_IOV_ETH].iov_len = sizeof(tcp4_eth_src);
-		iov[TCP_IOV_IP].iov_base = &tcp4_payload_ip[i];
-		iov[TCP_IOV_IP].iov_len = sizeof(tcp4_payload_ip[i]);
+		iov[TCP_IOV_ETH] = IOV_OF_LVALUE(tcp4_eth_src);
+		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp4_payload_ip[i]);
 		iov[TCP_IOV_PAYLOAD].iov_base = &tcp4_payload[i];
 	}
 
@@ -966,9 +965,8 @@ static void tcp_sock4_iov_init(const struct ctx *c)
 
 		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp4_flags_tap_hdr[i]);
 		iov[TCP_IOV_ETH].iov_base = &tcp4_eth_src;
-		iov[TCP_IOV_ETH].iov_len = sizeof(tcp4_eth_src);
-		iov[TCP_IOV_IP].iov_base = &tcp4_flags_ip[i];
-		iov[TCP_IOV_IP].iov_len = sizeof(tcp4_flags_ip[i]);
+		iov[TCP_IOV_ETH] = IOV_OF_LVALUE(tcp4_eth_src);
+		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp4_flags_ip[i]);
 		iov[TCP_IOV_PAYLOAD].iov_base = &tcp4_flags[i];
 	}
 }
@@ -1001,10 +999,8 @@ static void tcp_sock6_iov_init(const struct ctx *c)
 		iov = tcp6_l2_iov[i];
 
 		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp6_payload_tap_hdr[i]);
-		iov[TCP_IOV_ETH].iov_base = &tcp6_eth_src;
-		iov[TCP_IOV_ETH].iov_len = sizeof(tcp6_eth_src);
-		iov[TCP_IOV_IP].iov_base = &tcp6_payload_ip[i];
-		iov[TCP_IOV_IP].iov_len = sizeof(tcp6_payload_ip[i]);
+		iov[TCP_IOV_ETH] = IOV_OF_LVALUE(tcp6_eth_src);
+		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp6_payload_ip[i]);
 		iov[TCP_IOV_PAYLOAD].iov_base = &tcp6_payload[i];
 	}
 
@@ -1012,10 +1008,8 @@ static void tcp_sock6_iov_init(const struct ctx *c)
 		iov = tcp6_l2_flags_iov[i];
 
 		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp6_flags_tap_hdr[i]);
-		iov[TCP_IOV_ETH].iov_base = &tcp6_eth_src;
-		iov[TCP_IOV_ETH].iov_len = sizeof(tcp6_eth_src);
-		iov[TCP_IOV_IP].iov_base = &tcp6_flags_ip[i];
-		iov[TCP_IOV_IP].iov_len = sizeof(tcp6_flags_ip[i]);
+		iov[TCP_IOV_ETH] = IOV_OF_LVALUE(tcp6_eth_src);
+		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp6_flags_ip[i]);
 		iov[TCP_IOV_PAYLOAD].iov_base = &tcp6_flags[i];
 	}
 }
diff --git a/udp.c b/udp.c
index 2d27eae..7186fae 100644
--- a/udp.c
+++ b/udp.c
@@ -113,6 +113,7 @@
 
 #include "checksum.h"
 #include "util.h"
+#include "iov.h"
 #include "ip.h"
 #include "siphash.h"
 #include "inany.h"
@@ -315,8 +316,7 @@ static void udp_sock4_iov_init_one(const struct ctx *c, size_t i)
 		.iph = L2_BUF_IP4_INIT(IPPROTO_UDP)
 	};
 
-	siov->iov_base	= buf->data;
-	siov->iov_len	= sizeof(buf->data);
+	*siov		= IOV_OF_LVALUE(buf->data);
 
 	mh->msg_name	= &buf->s_in;
 	mh->msg_namelen	= sizeof(buf->s_in);
@@ -343,8 +343,7 @@ static void udp_sock6_iov_init_one(const struct ctx *c, size_t i)
 		.ip6h = L2_BUF_IP6_INIT(IPPROTO_UDP)
 	};
 
-	siov->iov_base	= buf->data;
-	siov->iov_len	= sizeof(buf->data);
+	*siov		= IOV_OF_LVALUE(buf->data);
 
 	mh->msg_name	= &buf->s_in6;
 	mh->msg_namelen	= sizeof(buf->s_in6);