[PATCH v3 02/11] ip: Add IN4_MASK() macro for IPv4 netmask calculation

[Jon Maloy <jmaloy@redhat.com>]

Add a convenience macro to compute an IPv4 netmask from a prefix length.
This simplifies netmask calculations throughout the codebase.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>
---
 conf.c | 2 +-
 dhcp.c | 2 +-
 ip.h   | 2 ++
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/conf.c b/conf.c
index 98d5d17..5188c02 100644
--- a/conf.c
+++ b/conf.c
@@ -1147,7 +1147,7 @@ static void conf_print(const struct ctx *c)
 		if (!c->no_dhcp) {
 			uint32_t mask;
 
-			mask = htonl(0xffffffff << (32 - c->ip4.prefix_len));
+			mask = IN4_MASK(c->ip4.prefix_len);
 
 			info("DHCP:");
 			info("    assign: %s",
diff --git a/dhcp.c b/dhcp.c
index 6b9c2e3..c552f01 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -404,7 +404,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 
 	info("    from %s", eth_ntop(m->chaddr, macstr, sizeof(macstr)));
 
-	mask.s_addr = htonl(0xffffffff << (32 - c->ip4.prefix_len));
+	mask.s_addr = IN4_MASK(c->ip4.prefix_len);
 	memcpy(opts[1].s,  &mask,                sizeof(mask));
 	memcpy(opts[3].s,  &c->ip4.guest_gw,     sizeof(c->ip4.guest_gw));
 	memcpy(opts[54].s, &c->ip4.our_tap_addr, sizeof(c->ip4.our_tap_addr));
diff --git a/ip.h b/ip.h
index bd28640..c829d84 100644
--- a/ip.h
+++ b/ip.h
@@ -17,6 +17,8 @@
 	(ntohl(((struct in_addr *)(a))->s_addr) >> IN_CLASSA_NSHIFT == IN_LOOPBACKNET)
 #define IN4_IS_ADDR_MULTICAST(a) \
 	(IN_MULTICAST(ntohl(((struct in_addr *)(a))->s_addr)))
+#define IN4_MASK(prefix_len) \
+	(htonl(0xffffffff << (128 - (prefix_len))))
 #define IN4_ARE_ADDR_EQUAL(a, b) \
 	(((struct in_addr *)(a))->s_addr == ((struct in_addr *)b)->s_addr)
 #define IN4ADDR_LOOPBACK_INIT \
-- 
2.52.0