genetlink: Optimize and one bug fix in genl_generate_id()

1. GENL_MIN_ID is a valid id -> no need to start at
   GENL_MIN_ID + 1.
2. Avoid going through the ids two times: If we start at
   GENL_MIN_ID+1 (*or bigger*) and all ids are over!, the
   code iterates through the list twice (*or lesser*).
3. Simplify code - no need to start at idx=0 which gets
   reset to GENL_MIN_ID.

Patch on net-next-2.6. Reboot test shows that first id
passed to genl_register_family was 16, next two were
GENL_ID_GENERATE and genl_generate_id returned 17 & 18
(user level testing of same code shows expected values
across entire range of MIN/MAX).
Signed-off-by: NKrishna Kumar <krkumar2@in.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/netlink/genetlink.c

@@ -97,25 +97,17 @@ static struct genl_ops *genl_get_cmd(u8 cmd, struct genl_family *family)
 */
 static inline u16 genl_generate_id(void)
 {
-	static u16 id_gen_idx;
-	int overflowed = 0;
+	static u16 id_gen_idx = GENL_MIN_ID;
+	int i;
 
-	do {
-		if (id_gen_idx == 0)
+	for (i = 0; i <= GENL_MAX_ID - GENL_MIN_ID; i++) {
+		if (!genl_family_find_byid(id_gen_idx))
+			return id_gen_idx;
+		if (++id_gen_idx > GENL_MAX_ID)
 			id_gen_idx = GENL_MIN_ID;
+	}
 
-		if (++id_gen_idx > GENL_MAX_ID) {
-			if (!overflowed) {
-				overflowed = 1;
-				id_gen_idx = 0;
-				continue;
-			} else
-				return 0;
-		}
-
-	} while (genl_family_find_byid(id_gen_idx));
-
-	return id_gen_idx;
+	return 0;
 }
 
 static struct genl_multicast_group notify_grp;