udhcp: add inline docs; small code shrink

function                                             old     new   delta
send_packet                                          103      87     -16
udhcpc_main                                         2359    2323     -36

networking/udhcp/clientpacket.c

@@ -78,6 +78,23 @@ static void add_param_req_option(struct dhcpMessage *packet)
 	}
 }
 
+/* RFC 2131
+ * 4.4.4 Use of broadcast and unicast
+ *
+ * The DHCP client broadcasts DHCPDISCOVER, DHCPREQUEST and DHCPINFORM
+ * messages, unless the client knows the address of a DHCP server.
+ * The client unicasts DHCPRELEASE messages to the server. Because
+ * the client is declining the use of the IP address supplied by the server,
+ * the client broadcasts DHCPDECLINE messages.
+ *
+ * When the DHCP client knows the address of a DHCP server, in either
+ * INIT or REBOOTING state, the client may use that address
+ * in the DHCPDISCOVER or DHCPREQUEST rather than the IP broadcast address.
+ * The client may also use unicast to send DHCPINFORM messages
+ * to a known DHCP server. If the client receives no response to DHCP
+ * messages sent to the IP address of a known DHCP server, the DHCP
+ * client reverts to using the IP broadcast address.
+ */
 
 static int raw_bcast_from_client_config_ifindex(struct dhcpMessage *packet)
 {
@@ -90,7 +107,6 @@ static int raw_bcast_from_client_config_ifindex(struct dhcpMessage *packet)
 
 #if ENABLE_FEATURE_UDHCPC_ARPING
 /* Broadcast a DHCP decline message */
-//FIXME: maybe it should be unicast?
 int FAST_FUNC send_decline(uint32_t xid, uint32_t server, uint32_t requested)
 {
 	struct dhcpMessage packet;
@@ -128,7 +144,9 @@ int FAST_FUNC send_discover(uint32_t xid, uint32_t requested)
 
 
 /* Broadcasts a DHCP request message */
-//FIXME: maybe it should be unicast?
+/* RFC 2131 3.1 paragraph 3:
+ * "The client _broadcasts_ a DHCPREQUEST message..."
+ */
 int FAST_FUNC send_select(uint32_t xid, uint32_t server, uint32_t requested)
 {
 	struct dhcpMessage packet;

networking/udhcp/common.h

@@ -27,21 +27,23 @@ extern const uint8_t MAC_BCAST_ADDR[6]; /* six all-ones */
 #define DHCP_OPTIONS_BUFSIZE  308
 
 struct dhcpMessage {
-	uint8_t op;
+	uint8_t op;      /* 1 = BOOTREQUEST, 2 = BOOTREPLY */
-	uint8_t htype;
+	uint8_t htype;   /* hardware address type. 1 = 10mb ethernet */
-	uint8_t hlen;
+	uint8_t hlen;    /* hardware address length */
-	uint8_t hops;
+	uint8_t hops;    /* used by relay agents only */
-	uint32_t xid;
+	uint32_t xid;    /* unique id */
-	uint16_t secs;
+	uint16_t secs;   /* elapsed since client began acquisition/renewal */
-	uint16_t flags;
+	uint16_t flags;  /* only one flag so far: */
-	uint32_t ciaddr;
+#define BROADCAST_FLAG 0x8000 /* "I need broadcast replies" */
-	uint32_t yiaddr;
+	uint32_t ciaddr; /* client IP (if client is in BOUND, RENEW or REBINDING state) */
-	uint32_t siaddr;
+	uint32_t yiaddr; /* 'your' (client) IP address */
-	uint32_t giaddr;
+	uint32_t siaddr; /* IP address of next server to use in bootstrap,
-	uint8_t chaddr[16];
+	                  * returned in DHCPOFFER, DHCPACK by server */
-	uint8_t sname[64];
+	uint32_t giaddr; /* relay agent IP address */
-	uint8_t file[128];
+	uint8_t chaddr[16];/* link-layer client hardware address (MAC) */
-	uint32_t cookie;
+	uint8_t sname[64]; /* server host name (ASCIZ) */
+	uint8_t file[128]; /* boot file name (ASCIZ) */
+	uint32_t cookie;   /* fixed first four option bytes (99,130,83,99 dec) */
 	uint8_t options[DHCP_OPTIONS_BUFSIZE + CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS];
 } PACKED;
 

networking/udhcp/dhcpc.c

@@ -452,7 +452,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 		}
 
 		/* select() didn't timeout, something did happen. */
-		/* Is is a packet? */
+		/* Is it a packet? */
 		if (listen_mode != LISTEN_NONE && FD_ISSET(sockfd, &rfds)) {
 			int len;
 			/* A packet is ready, read it */
@@ -474,7 +474,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 				continue;
 
 			if (packet.xid != xid) {
-				DEBUG("Ignoring XID %x (our xid is %x)",
+				DEBUG("Ignoring xid %x (our xid is %x)",
 					(unsigned)packet.xid, (unsigned)xid);
 				continue;
 			}
@@ -524,17 +524,24 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 						bb_error_msg("no lease time with ACK, using 1 hour lease");
 						lease_seconds = 60 * 60;
 					} else {
-						/* can be misaligned, thus memcpy */
+						/* it IS unaligned sometimes, don't "optimize" */
-						memcpy(&lease_seconds, temp, 4);
+						lease_seconds = get_unaligned_u32p((uint32_t*)temp);
 						lease_seconds = ntohl(lease_seconds);
 						lease_seconds &= 0x0fffffff; /* paranoia: must not be prone to overflows */
 						if (lease_seconds < 10) /* and not too small */
 							lease_seconds = 10;
 					}
-//FIXME: why do we check ARP only after we've got DHCPACK?
-//Shouldn't we do it immediately after DHCPOFFER?
 #if ENABLE_FEATURE_UDHCPC_ARPING
 					if (opt & OPT_a) {
+/* RFC 2131 3.1 paragraph 5:
+ * "The client receives the DHCPACK message with configuration
+ * parameters. The client SHOULD perform a final check on the
+ * parameters (e.g., ARP for allocated network address), and notes
+ * the duration of the lease specified in the DHCPACK message. At this
+ * point, the client is configured. If the client detects that the
+ * address is already in use (e.g., through the use of ARP),
+ * the client MUST send a DHCPDECLINE message to the server and restarts
+ * the configuration process..." */
 						if (!arpping(packet.yiaddr,
 							    (uint32_t) 0,
 							    client_config.arp,
@@ -542,8 +549,6 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 						) {
 							bb_info_msg("offered address is in use "
 								"(got ARP reply), declining");
-//NB: not clear whether it should be unicast or bcast.
-//Currently it is a bcast. Why?
 							send_decline(xid, server_addr, packet.yiaddr);
 
 							if (state != REQUESTING)

networking/udhcp/options.h

@@ -78,16 +78,14 @@ enum {
 #define ETH_10MB		1
 #define ETH_10MB_LEN		6
 
-#define DHCPDISCOVER		1
+#define DHCPDISCOVER		1 /* client -> server */
-#define DHCPOFFER		2
+#define DHCPOFFER		2 /* client <- server */
-#define DHCPREQUEST		3
+#define DHCPREQUEST		3 /* client -> server */
-#define DHCPDECLINE		4
+#define DHCPDECLINE		4 /* client -> server */
-#define DHCPACK			5
+#define DHCPACK			5 /* client <- server */
-#define DHCPNAK			6
+#define DHCPNAK			6 /* client <- server */
-#define DHCPRELEASE		7
+#define DHCPRELEASE		7 /* client -> server */
-#define DHCPINFORM		8
+#define DHCPINFORM		8 /* client -> server */
-
-#define BROADCAST_FLAG		0x8000
 
 #define OPTION_FIELD		0
 #define FILE_FIELD		1

networking/udhcp/packet.c

@@ -18,12 +18,12 @@
 void FAST_FUNC udhcp_init_header(struct dhcpMessage *packet, char type)
 {
 	memset(packet, 0, sizeof(struct dhcpMessage));
-	packet->op = BOOTREQUEST;
+	packet->op = BOOTREQUEST; /* if client to a server */
 	switch (type) {
 	case DHCPOFFER:
 	case DHCPACK:
 	case DHCPNAK:
-		packet->op = BOOTREPLY;
+		packet->op = BOOTREPLY; /* if server to client */
 	}
 	packet->htype = ETH_10MB;
 	packet->hlen = ETH_10MB_LEN;
@@ -65,7 +65,7 @@ int FAST_FUNC udhcp_recv_kernel_packet(struct dhcpMessage *packet, int fd)
 				if (vendor[OPT_LEN - 2] == (uint8_t)strlen(broken_vendors[i])
 				 && !strncmp((char*)vendor, broken_vendors[i], vendor[OPT_LEN - 2])
 				) {
-					DEBUG("broken client (%s), forcing broadcast",
+					DEBUG("broken client (%s), forcing broadcast replies",
 						broken_vendors[i]);
 					packet->flags |= htons(BROADCAST_FLAG);
 				}
@@ -74,7 +74,7 @@ int FAST_FUNC udhcp_recv_kernel_packet(struct dhcpMessage *packet, int fd)
 			if (vendor[OPT_LEN - 2] == (uint8_t)(sizeof("MSFT 98")-1)
 			 && memcmp(vendor, "MSFT 98", sizeof("MSFT 98")-1) == 0
 			) {
-				DEBUG("broken client (%s), forcing broadcast", "MSFT 98");
+				DEBUG("broken client (%s), forcing broadcast replies", "MSFT 98");
 				packet->flags |= htons(BROADCAST_FLAG);
 			}
 #endif

networking/udhcp/serverpacket.c

@@ -50,7 +50,7 @@ static int send_packet_to_client(struct dhcpMessage *payload, int force_broadcas
 		DEBUG("unicasting packet to client ciaddr");
 		ciaddr = payload->ciaddr;
 		chaddr = payload->chaddr;
-	} else if (ntohs(payload->flags) & BROADCAST_FLAG) {
+	} else if (payload->flags & htons(BROADCAST_FLAG)) {
 		DEBUG("broadcasting packet to client (requested)");
 		ciaddr = INADDR_BROADCAST;
 		chaddr = MAC_BCAST_ADDR;