[RFC 02/12] ip: Add ip4_default_prefix_len() helper function for class-based prefix

[Jon Maloy <jmaloy@redhat.com>]

We add a helper function to calculate the default IPv4 prefix length
based on address class. This is used to replace the current inline
calculation in conf_ip4(), and is also a preparation for more uses
of this functionality in the coming commits.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>
---
 conf.c | 15 +++------------
 ip.c   | 21 +++++++++++++++++++++
 ip.h   |  2 ++
 3 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/conf.c b/conf.c
index 0e96f36..31acc20 100644
--- a/conf.c
+++ b/conf.c
@@ -733,18 +733,9 @@ static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4,
 	}
 
 	/* Apply default prefix_len to first address if not set */
-	if (!ip4->addrs[0].prefix_len) {
-		in_addr_t a = ntohl(ip4->addrs[0].addr.s_addr);
-
-		if (IN_CLASSA(a))
-			ip4->addrs[0].prefix_len = 8;
-		else if (IN_CLASSB(a))
-			ip4->addrs[0].prefix_len = 16;
-		else if (IN_CLASSC(a))
-			ip4->addrs[0].prefix_len = 24;
-		else
-			ip4->addrs[0].prefix_len = 32;
-	}
+	if (!ip4->addrs[0].prefix_len)
+		ip4->addrs[0].prefix_len =
+			ip4_default_prefix_len(&ip4->addrs[0].addr);
 
 	ip4->addr_seen = ip4->addrs[0].addr;
 
diff --git a/ip.c b/ip.c
index 9a7f4c5..2519c71 100644
--- a/ip.c
+++ b/ip.c
@@ -13,6 +13,8 @@
  */
 
 #include <stddef.h>
+#include <netinet/in.h>
+
 #include "util.h"
 #include "ip.h"
 
@@ -67,3 +69,22 @@ found:
 	*proto = nh;
 	return true;
 }
+
+/**
+ * ip4_default_prefix_len() - Get default prefix length for IPv4 address
+ * @addr:	IPv4 address
+ *
+ * Return: prefix length based on address class (8/16/24), or 32 for other
+ */
+int ip4_default_prefix_len(const struct in_addr *addr)
+{
+	in_addr_t a = ntohl(addr->s_addr);
+
+	if (IN_CLASSA(a))
+		return 8;
+	if (IN_CLASSB(a))
+		return 16;
+	if (IN_CLASSC(a))
+		return 24;
+	return 32;
+}
diff --git a/ip.h b/ip.h
index 748cb1f..065b78b 100644
--- a/ip.h
+++ b/ip.h
@@ -139,6 +139,8 @@ static const struct in_addr in4addr_broadcast = { 0xffffffff };
 #define IP4_MAX_ADDRS		8
 #define IP6_MAX_ADDRS		16
 
+int ip4_default_prefix_len(const struct in_addr *addr);
+
 /**
  * struct ip4_addr_entry - IPv4 address with prefix length
  * @addr:		IPv4 address
-- 
2.51.1