dhcpv4: improve error when a prefix is too long

If a user tries to enable dhcpv4 on an interface with a /29, odhcp won't work.
The logs will only contain a message that doesn't help identify the problem.
It'd be idea to support any prefix with a valid pool, but at least this would
point a confused user in the right direction.

Signed-off-by: Ross Vandegrift <ross@kallisti.us>

diff --git a/src/dhcpv4.c b/src/dhcpv4.c
index 2b2f41e01cc3469f623186e425e31a835dc3eed8..3191ff2cc473d53b2e296daf8afbb76e029c97cb 100644 (file)
--- a/src/dhcpv4.c
+++ b/src/dhcpv4.c
@@ -37,6 +37,7 @@
 
 #define PACKET_SIZE(start, end) (((uint8_t *)end - (uint8_t *)start) < DHCPV4_MIN_PACKET_SIZE ? \
                                 DHCPV4_MIN_PACKET_SIZE : (uint8_t *)end - (uint8_t *)start)
+#define MAX_PREFIX_LEN 28
 
 static void dhcpv4_netevent_cb(unsigned long event, struct netevent_handler_info *info);
 static int setup_dhcpv4_addresses(struct interface *iface);
@@ -248,9 +249,9 @@ static int setup_dhcpv4_addresses(struct interface *iface)
                }
        }
 
-       /* Don't allocate IP range for subnets bigger than 28 */
-       if (iface->addr4[0].prefix > 28) {
-               syslog(LOG_WARNING, "Auto allocation of DHCP range fails on %s", iface->name);
+       /* Don't allocate IP range for subnets smaller than /28 */
+       if (iface->addr4[0].prefix > MAX_PREFIX_LEN) {
+               syslog(LOG_WARNING, "Auto allocation of DHCP range fails on %s (prefix length must be < %d).", iface->name, MAX_PREFIX_LEN + 1);
                return -1;
        }