[PATCH 6/7] iov: Helper macro to construct iovs covering existing variables or fields

[David Gibson <david@gibson.dropbear.id.au>]

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>
---
 iov.h |  3 +++
 tap.c |  3 +--
 tcp.c | 24 +++++++++---------------
 udp.c |  7 +++----
 4 files changed, 16 insertions(+), 21 deletions(-)

diff --git a/iov.h b/iov.h
index 6058af77..5668ca5f 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 6a08cca6..5db7b169 100644
--- a/tap.c
+++ b/tap.c
@@ -79,8 +79,7 @@ void tap_send_single(const struct ctx *c, const void *data, size_t len)
 	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 ad409fc5..27c06958 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 1a4c02f4..545212c5 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);
-- 
@@ -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);
-- 
2.44.0