lighttpd 学习笔记一

从server.c的main函数看起，启动流程大体如下：

server_init 函数初始化lighttpd 的server 数据结构，涉及到其中一些buffer,array的结构初始化工作，主要参考的数据结构buffer,array,chunkqueue等等

通过启动参数-f 读取配置文件 config_read

if (!i_am_root && (geteuid() == 0 || getegid() == 0)) {
		/* we are setuid-root */

		log_error_write(srv, __FILE__, __LINE__, "s",
				"Are you nuts ? Don't apply a SUID bit to this binary");

		server_free(srv);
		return -1;
}

这段代码是当lighttpd binary 被setuid(类似 chmod 4755)时，禁止运行，不明白为什么要这样处理，回头再了解一下
i_am_root 是 getuid==0的结果，即root用户 getuid会返回 0，非root会返回正整数

后面比较奇怪的地方时

if (srv->event_handler == FDEVENT_HANDLER_SELECT) {
		/* select limits itself
		 *
		 * as it is a hard limit and will lead to a segfault we add some safety
		 * */
		srv->max_fds = FD_SETSIZE - 200;
	} else {
		srv->max_fds = 4096;
	}

默认没有修改配置文件的情况下，linux 2.6的srv->event_handler应该是epoll，就是执行else分支，我用gdb也是这个结果，为什么max_fds最多只有4096呢？libevent里直接就是rlimit里的 rlim_cur,通常会被设置成65535

接下来比较重要的是  network_init 调用(参考network.c文件)

在network_init中也就是调用 socket,setsocketopt,bind,listen等操作，创建出一个listen socket

#ifdef HAVE_FORK
	/* start watcher and workers */
	num_childs = srv->srvconf.max_worker;
	if (num_childs > 0) {
		int child = 0;
		while (!child && !srv_shutdown && !graceful_shutdown) {
			if (num_childs > 0) {
				switch (fork()) {
				case -1:
					return -1;
				case 0:
					child = 1;
					break;
				default:
					num_childs--;
					break;
				}
			} else {
				int status;

				if (-1 != wait(&status)) {
					/** 
					 * one of our workers went away 
					 */
					num_childs++;
				} else {
					switch (errno) {
					case EINTR:
						/**
						 * if we receive a SIGHUP we have to close our logs ourself as we don't 
						 * have the mainloop who can help us here
						 */
						if (handle_sig_hup) {
							handle_sig_hup = 0;

							log_error_cycle(srv);

							/**
							 * forward to all procs in the process-group
							 * 
							 * we also send it ourself
							 */
							if (!forwarded_sig_hup) {
								forwarded_sig_hup = 1;
								kill(0, SIGHUP);
							}
						}
						break;
					default:
						break;
					}
				}
			}
		}

		/**
		 * for the parent this is the exit-point 
		 */
		if (!child) {
			/** 
			 * kill all children too 
			 */
			if (graceful_shutdown) {
				kill(0, SIGINT);
			} else if (srv_shutdown) {
				kill(0, SIGTERM);
			}

			log_error_close(srv);
			network_close(srv);
			connections_free(srv);
			plugins_free(srv);
			server_free(srv);
			return 0;
		}
	}
#endif

这段代码的功能是fork出若干child进程，然后父进程投入睡眠等待子进程退出，如果有退出的子进程，父进程会马上在fork出新的子进程，就是所谓的 watcher - worker的模型，这个网上的资料也有很清楚的论述

接下来子进程（可能很多个）开始注册事件
lighttpd也是使用event-driven模型，fdevents是全局的事件处理器数据结构，实现的功能类似于libevent

if (NULL == (srv->ev = fdevent_init(srv->max_fds + 1, srv->event_handler))) {
		log_error_write(srv, __FILE__, __LINE__,
				"s", "fdevent_init failed");
		return -1;
	}

fdevent_init初始化事件处理器
具体的事件选择应该已经通过读取配置文件设置好了，以epoll为例子，实际执行的是

ev->type = FDEVENT_HANDLER_LINUX_SYSEPOLL;
#define SET(x) \
	ev->x = fdevent_linux_sysepoll_##x;

	SET(free);
	SET(poll);

	SET(event_del);
	SET(event_add);

	SET(event_next_fdndx);
	SET(event_get_fd);
	SET(event_get_revent);

	if (-1 == (ev->epoll_fd = epoll_create(ev->maxfds))) {
		fprintf(stderr, "%s.%d: epoll_create failed (%s), try to set server.event-handler = \"poll\" or \"select\"\n",
			__FILE__, __LINE__, strerror(errno));

		return -1;
	}

	if (-1 == fcntl(ev->epoll_fd, F_SETFD, FD_CLOEXEC)) {
		fprintf(stderr, "%s.%d: epoll_create failed (%s), try to set server.event-handler = \"poll\" or \"select\"\n",
			__FILE__, __LINE__, strerror(errno));

		close(ev->epoll_fd);

		return -1;
	}

	ev->epoll_events = malloc(ev->maxfds * sizeof(*ev->epoll_events));

#define SET(x) \
ev->x = fdevent_linux_sysepoll_##x;

##的作用是字符连接即初始化函数指针
ev->free=fdevent_linux_sysepoll_free等操作

通过上面代码初始化好了事件处理器srv->ev

接下来调用 network_register_fdevents (文件network.c)

int network_register_fdevents(server *srv) {
	size_t i;

	if (-1 == fdevent_reset(srv->ev)) {
		return -1;
	}

	/* register fdevents after reset */
	for (i = 0; i < srv->srv_sockets.used; i++) {
		server_socket *srv_socket = srv->srv_sockets.ptr[i];

		fdevent_register(srv->ev, srv_socket->fd, network_server_handle_fdevent, srv_socket);
		fdevent_event_add(srv->ev, &(srv_socket->fde_ndx), srv_socket->fd, FDEVENT_IN);
	}
	return 0;
}

此时srv->srv_sockets.used应该为1,就是刚刚建立的listen fd

fdevent_register代码

int fdevent_register(fdevents *ev, int fd, fdevent_handler handler, void *ctx) {
	fdnode *fdn;

	fdn = fdnode_init();
	fdn->handler = handler;
	fdn->fd      = fd;
	fdn->ctx     = ctx;

	ev->fdarray[fd] = fdn;

	return 0;
}

fdarray用于保存fd与对应回调handler及参数ctx之间的关系，将来能以O(1)的性能查找到某个fd对应的回调函数及参数

server.c最后就是一个巨大的循环

/* main-loop */
	while (!srv_shutdown) {
		//巨大的循环代码段
	}

	if (srv->srvconf.pid_file->used &&
	    srv->srvconf.changeroot->used == 0 &&
	    0 == graceful_shutdown) {
		if (0 != unlink(srv->srvconf.pid_file->ptr)) {
			if (errno != EACCES && errno != EPERM) {
				log_error_write(srv, __FILE__, __LINE__, "sbds",
						"unlink failed for:",
						srv->srvconf.pid_file,
						errno,
						strerror(errno));
			}
		}
	}

#ifdef HAVE_SIGACTION
	log_error_write(srv, __FILE__, __LINE__, "sdsd", 
			"server stopped by UID =",
			last_sigterm_info.si_uid,
			"PID =",
			last_sigterm_info.si_pid);
#else
	log_error_write(srv, __FILE__, __LINE__, "s", 
			"server stopped");
#endif

	/* clean-up */
	log_error_close(srv);
	network_close(srv);
	connections_free(srv);
	plugins_free(srv);
	server_free(srv);

	return 0;

由于fork会原样复制父进程的heap和stack区，并保持独立，所以fork方式的好处就是完全不需要共享任何东西，代价是内存占用量要比较多