dhcpc.c

该模块功能可以实现DHCP

		case 's':
			client_config.script = optarg;
			break;
		case 'v':
			printf("udhcpcd, version %s\n\n", VERSION);
			exit_client(0);
			break;
		default:
			show_usage();
		}
	}

	OPEN_LOG("udhcpc");
	LOG(LOG_INFO, "udhcp client (v%s) started", VERSION);

	pid_fd = pidfile_acquire(client_config.pidfile);
	pidfile_write_release(pid_fd);

	if (read_interface(client_config.interface, &client_config.ifindex, 
			   NULL, client_config.arp) < 0)
		exit_client(1);
		
	if (!client_config.clientid) {
		client_config.clientid = xmalloc(6 + 3);
		client_config.clientid[OPT_CODE] = DHCP_CLIENT_ID;
		client_config.clientid[OPT_LEN] = 7;
		client_config.clientid[OPT_DATA] = 1;
		memcpy(client_config.clientid + 3, client_config.arp, 6);
	}

	/* ensure that stdin/stdout/stderr are never returned by pipe() */
	if (fcntl(STDIN_FILENO, F_GETFL) == -1)
		(void) open("/dev/null", O_RDONLY);
	if (fcntl(STDOUT_FILENO, F_GETFL) == -1)
		(void) open("/dev/null", O_WRONLY);
	if (fcntl(STDERR_FILENO, F_GETFL) == -1)
		(void) open("/dev/null", O_WRONLY);	

	/* setup signal handlers */
	pipe(signal_pipe);
	signal(SIGUSR1, signal_handler);
	signal(SIGUSR2, signal_handler);
	signal(SIGTERM, signal_handler);
	
	state = INIT_SELECTING;
	run_script(NULL, "deconfig");
	change_mode(LISTEN_RAW);

	for (;;) {

		tv.tv_sec = timeout - get_time(0);
		tv.tv_usec = 0;
		FD_ZERO(&rfds);

		if (listen_mode != LISTEN_NONE && fd < 0) {
			if (listen_mode == LISTEN_KERNEL)
				fd = listen_socket(INADDR_ANY, CLIENT_PORT, client_config.interface);
			else
				fd = raw_socket(client_config.ifindex);
			if (fd < 0) {
				LOG(LOG_ERR, "FATAL: couldn't listen on socket, %s", strerror(errno));
				exit_client(0);
			}
		}
		if (fd >= 0) FD_SET(fd, &rfds);
		FD_SET(signal_pipe[0], &rfds);		

		if (tv.tv_sec > 0) {
			DEBUG(LOG_INFO, "Waiting on select...\n");
			max_fd = signal_pipe[0] > fd ? signal_pipe[0] : fd;
			retval = select(max_fd + 1, &rfds, NULL, NULL, &tv);
		} else retval = 0; /* If we already timed out, fall through */

		now = get_time(0);
		if (retval == 0) {
			/* timeout dropped to zero */
			switch (state) {
			case INIT_SELECTING:
				if (packet_num < 3) {
					if (packet_num == 0)
						xid = random_xid();

					/* send discover packet */
					send_discover(xid, requested_ip); /* broadcast */
					
					timeout = now + ((packet_num == 2) ? 4 : 2);
					packet_num++;
				} else {
					if (client_config.background_if_no_lease) {
						LOG(LOG_INFO, "No lease, forking to background.");
						background();
					} else if (client_config.abort_if_no_lease) {
						LOG(LOG_INFO, "No lease, failing.");
						exit_client(1);
				  	}
					/* wait to try again */
					packet_num = 0;
					timeout = now + 5;	// change wait time from 60 to 5 seconds , by honor
				}
				break;
			case RENEW_REQUESTED:
			case REQUESTING:
				if (packet_num < 3) {
					/* send request packet */
					if (state == RENEW_REQUESTED)
						send_renew(xid, server_addr, requested_ip); /* unicast */
					else send_selecting(xid, server_addr, requested_ip); /* broadcast */
					
					timeout = now + ((packet_num == 2) ? 10 : 2);
					packet_num++;
				} else {
					/* timed out, go back to init state */
					if (state == RENEW_REQUESTED) run_script(NULL, "deconfig");
					state = INIT_SELECTING;
					timeout = now;
					packet_num = 0;
					change_mode(LISTEN_RAW);
				}
				break;
			case BOUND:
				/* Lease is starting to run out, time to enter renewing state */
				state = RENEWING;
				//change_mode(LISTEN_KERNEL);
				change_mode(LISTEN_RAW);	// Some DHCP server send broadcast ACK after they receive a REQUEST during RENEWING state, by honor
				DEBUG(LOG_INFO, "Entering renew state");
				/* fall right through */
			case RENEWING:
				/* Either set a new T1, or enter REBINDING state */
				if ((t2 - t1) <= (lease / 14400 + 1)) {
					/* timed out, enter rebinding state */
					state = REBINDING;
					timeout = now + (t2 - t1);
					DEBUG(LOG_INFO, "Entering rebinding state");
				} else {
					/* send a request packet */
					send_renew(xid, server_addr, requested_ip); /* unicast */
					
					t1 = (t2 - t1) / 2 + t1;
					timeout = t1 + start;
				}
				break;
			case REBINDING:
				/* Either set a new T2, or enter INIT state */
				if ((lease - t2) <= (lease / 14400 + 1)) {
					/* timed out, enter init state */
					state = INIT_SELECTING;
					LOG(LOG_INFO, "Lease lost, entering init state");
					run_script(NULL, "deconfig");
					timeout = now;
					packet_num = 0;
					change_mode(LISTEN_RAW);
				} else {
					/* send a request packet */
					send_renew(xid, 0, requested_ip); /* broadcast */

					t2 = (lease - t2) / 2 + t2;
					timeout = t2 + start;
				}
				break;
			case RELEASED:
				/* yah, I know, *you* say it would never happen */
				timeout = 0x7fffffff;
				break;
			}
		} else if (retval > 0 && listen_mode != LISTEN_NONE && FD_ISSET(fd, &rfds)) {
			/* a packet is ready, read it */
			
			if (listen_mode == LISTEN_KERNEL)
				len = get_packet(&packet, fd);
			else len = get_raw_packet(&packet, fd);
			
			if (len == -1 && errno != EINTR) {
				DEBUG(LOG_INFO, "error on read, %s, reopening socket", strerror(errno));
				change_mode(listen_mode); /* just close and reopen */
			}
			if (len < 0) continue;
			
			if (packet.xid != xid) {
				DEBUG(LOG_INFO, "Ignoring XID %lx (our xid is %lx)",
					(unsigned long) packet.xid, xid);
				continue;
			}
			
			if ((message = get_option(&packet, DHCP_MESSAGE_TYPE)) == NULL) {
				DEBUG(LOG_ERR, "couldnt get option from packet -- ignoring");
				continue;
			}
			
			switch (state) {
			case INIT_SELECTING:
				/* Must be a DHCPOFFER to one of our xid's */
				if (*message == DHCPOFFER) {
					if ((temp = get_option(&packet, DHCP_SERVER_ID))) {
						memcpy(&server_addr, temp, 4);
						xid = packet.xid;
						requested_ip = packet.yiaddr;
						
						/* enter requesting state */
						state = REQUESTING;
						timeout = now;
						packet_num = 0;
					} else {
						DEBUG(LOG_ERR, "No server ID in message");
					}
				}
				break;
			case RENEW_REQUESTED:
			case REQUESTING:
			case RENEWING:
			case REBINDING:
				if (*message == DHCPACK) {
					if (!(temp = get_option(&packet, DHCP_LEASE_TIME))) {
						LOG(LOG_ERR, "No lease time with ACK, using 1 hour lease");
						lease = 60 * 60;
					} else {
						memcpy(&lease, temp, 4);
						lease = ntohl(lease);
					}
						
					/* enter bound state */
					t1 = lease / 2;
					
					/* little fixed point for n * .875 */
					t2 = (lease * 0x7) >> 3;
					temp_addr.s_addr = packet.yiaddr;
					LOG(LOG_INFO, "Lease of %s obtained, lease time %ld", 
						inet_ntoa(temp_addr), lease);
					start = now;
					timeout = t1 + start;
					requested_ip = packet.yiaddr;
					if (state != RENEWING && state !=REBINDING)
						run_script(&packet,
						   ((state == RENEWING || state == REBINDING) ? "renew" : "bound"));

					state = BOUND;
					change_mode(LISTEN_NONE);
					if (client_config.quit_after_lease) 
						exit_client(0);
					if (!client_config.foreground)
						background();

				} else if (*message == DHCPNAK) {
					/* return to init state */
					LOG(LOG_INFO, "Received DHCP NAK");
					run_script(&packet, "nak");
					if (state != REQUESTING)
						run_script(NULL, "deconfig");
					state = INIT_SELECTING;
					timeout = now;
					requested_ip = 0;
					packet_num = 0;
					change_mode(LISTEN_RAW);
					sleep(3); /* avoid excessive network traffic */
				}
				break;
			/* case BOUND, RELEASED: - ignore all packets */
			}	
		} else if (retval > 0 && FD_ISSET(signal_pipe[0], &rfds)) {
			if (read(signal_pipe[0], &sig, sizeof(sig)) < 0) {
				DEBUG(LOG_ERR, "Could not read signal: %s", 
					strerror(errno));
				continue; /* probably just EINTR */
			}
			switch (sig) {
			case SIGUSR1: 
				perform_renew();
				break;
			case SIGUSR2:
				perform_release();
				break;
			case SIGTERM:
				LOG(LOG_INFO, "Received SIGTERM");
				exit_client(0);
			}
		} else if (retval == -1 && errno == EINTR) {
			/* a signal was caught */		
		} else {
			/* An error occured */
			DEBUG(LOG_ERR, "Error on select");
		}
		
	}
	return 0;
}