dhcpv4_assign: rework the assignment logic

diff --git a/src/dhcpv4.c b/src/dhcpv4.c
index 1807c68b02ab9933dcdfc09a1498d155853444fe..462f641a0b6ab1b85ddf39ab4c0fabe222c3a831 100644 (file)
--- a/src/dhcpv4.c
+++ b/src/dhcpv4.c
@@ -502,50 +502,74 @@ static void handle_dhcpv4(void *addr, void *data, size_t len,
                        (struct sockaddr*)&dest, sizeof(dest));
 }
 
+static bool dhcpv4_test(struct interface *iface, uint32_t try)
+{
+       struct dhcpv4_assignment *c;
+       list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
+               if (c->addr == try) {
+                       return false;
+               }
+       }
+       return true;
+}
 
 static bool dhcpv4_assign(struct interface *iface,
                struct dhcpv4_assignment *assign, uint32_t raddr)
 {
-       const unsigned tries = 100;
        uint32_t start = ntohl(iface->dhcpv4_start.s_addr);
        uint32_t end = ntohl(iface->dhcpv4_end.s_addr);
        uint32_t count = end - start + 1;
 
+       // try to assign the IP the client asked for
+       if (start <= raddr && raddr <= end && dhcpv4_test(iface, raddr)) {
+               assign->addr = raddr;
+               list_add(&assign->head, &iface->dhcpv4_assignments);
+               syslog(LOG_DEBUG, "assigning the IP the client asked for: %u.%u.%u.%u",
+                               (assign->addr & 0xff000000) >> 24,
+                               (assign->addr & 0x00ff0000) >> 16,
+                               (assign->addr & 0x0000ff00) >> 8,
+                               (assign->addr & 0x000000ff));
+               return true;
+       }
+
        // Seed RNG with checksum of hwaddress
        uint32_t seed = 0;
-       for (size_t i = 0; i < sizeof(assign->hwaddr); ++i)
-               seed += assign->hwaddr[i];
+       for (size_t i = 0; i < sizeof(assign->hwaddr); ++i) {
+               // Knuth's multiplicative method
+               uint8_t o = assign->hwaddr[i];
+               seed += (o*2654435761) % UINT32_MAX;
+       }
        srand(seed);
 
-       // Try to assign up to 100x
-       for (unsigned i = 0; i < tries; ++i) {
-               uint32_t try = (((uint32_t)rand()) % count) + start;
-               if (i == 0 && raddr >= start && raddr <= end)
-                       try = raddr;
-               else if (i == tries - 1)
-                       try = start;
+       uint32_t try = (((uint32_t)rand()) % count) + start;
+
+       if (list_empty(&iface->dhcpv4_assignments)) {
+               assign->addr = try;
+               list_add(&assign->head, &iface->dhcpv4_assignments);
+               syslog(LOG_DEBUG, "assigning mapped IP (empty list): %u.%u.%u.%u",
+                               (assign->addr & 0xff000000) >> 24,
+                               (assign->addr & 0x00ff0000) >> 16,
+                               (assign->addr & 0x0000ff00) >> 8,
+                               (assign->addr & 0x000000ff));
+               return true;
+       }
 
-               if (list_empty(&iface->dhcpv4_assignments)) {
+       for (size_t i = 0; i < count; ++i) {
+               if (dhcpv4_test(iface, try)) {
+                       /* test was successful: IP address is not assigned, assign it */
                        assign->addr = try;
                        list_add(&assign->head, &iface->dhcpv4_assignments);
+                       syslog(LOG_DEBUG, "assigning mapped IP: %u.%u.%u.%u (try %d of %d)",
+                                       (assign->addr & 0xff000000) >> 24,
+                                       (assign->addr & 0x00ff0000) >> 16,
+                                       (assign->addr & 0x0000ff00) >> 8,
+                                       (assign->addr & 0x000000ff), i, count);
                        return true;
                }
-
-               struct dhcpv4_assignment *c;
-               list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
-                       if (c->addr > try) {
-                               assign->addr = try;
-                               list_add_tail(&assign->head, &c->head);
-                               return true;
-                       } else if (c->addr == try) {
-                               if (i < tries - 1)
-                                       break;
-                               else
-                                       ++try;
-                       }
-               }
+               try = (((try - start) + 1) % count) + start;
        }
 
+       syslog(LOG_DEBUG, "can't assign any IP address -> address space is full");
        return false;
 }