├── LICENSE ├── epoll_create分析 ├── epoll_ctl分析 ├── epoll_wait分析 └── 内核触发通知部分分析 /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. By contrast, 15 | the GNU General Public License is intended to guarantee your freedom to 16 | share and change all versions of a program--to make sure it remains free 17 | software for all its users. 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Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | -------------------------------------------------------------------------------- /epoll_create分析: -------------------------------------------------------------------------------- 1 | ******************************************************************** 2 | ***** epoll_create ***** 3 | ******************************************************************** 4 | epoll_create主要创建了一个fd descriptor,通过该fd可以找到对应的file结构体和eventpoll结构体 5 | 6 | SYSCALL_DEFINE1(epoll_create, int, size) 7 | { 8 | ...... 9 | return sys_epoll_create1(0); 10 | } 11 | epoll_create主要调用了内核系统调用函数sys_epoll_create1. 12 | 而sys_epoll_create1的函数定义原型为SYSCALL_DEFINE1(epoll_create1, int, flags). 13 | 14 | SYSCALL_DEFINE1(epoll_create1, int, flags) 15 | { 16 | /* 传递进来的flags为0, 为epoll_create传递的size大小没有起作用 */ 17 | int error; 18 | struct eventpoll *ep = NULL; 19 | ...... 20 | 21 | error = ep_alloc(&ep); 22 | /* eventpoll结构体主要在ep_alloc中开辟的. */ 23 | 24 | error = anon_inode_getfd("[eventpoll]", &eventpoll_fops, ep, 25 | flags & O_CLOEXEC); 26 | /* 在anon_inode_getfd中构造epoll_create返回的套接字的file和dentry资源,此处给该fd的f_op参数 27 | 赋值为event_poll_fops, 具体结构如下: 28 | 29 | static const struct file_operations eventpoll_fops = { 30 | .release= ep_eventpoll_release, 31 | .poll = ep_eventpoll_poll 32 | }; 33 | 34 | */ 35 | 36 | ...... 37 | } 38 | 39 | 接上文中的函数调用,接下来是ep_alloc函数 40 | static int ep_alloc(struct eventpoll **pep) 41 | { 42 | ...... 43 | user = get_current_user(); 44 | /*get_current_user引用struct user_struct结构体(用户结构体), 此处不做讨论*/ 45 | 46 | ep = kzalloc(sizeof(*ep), GFP_KERNEL); 47 | /* ep 为开辟的struct eventpoll结构体, 失败之后将调用free_uid*/ 48 | 49 | /* 锁的初始化 */ 50 | spin_lock_init(&ep->lock); 51 | mutex_init(&ep->mtx); 52 | 53 | /*初始化等待队列(基础结构为struct list_head), 一般sys_epoll_wait()函数用来使用*/ 54 | init_waitqueue_head(&ep->wq); 55 | /*初始化等待队列(基础结构为struct list_head), 一般file->poll()函数用来使用*/ 56 | init_waitqueue_head(&ep->poll_wait); 57 | 58 | /*初始化就绪队列*/ 59 | INIT_LIST_HEAD(&ep->rdllist); 60 | 61 | /* epoll的底层数据结构红黑树, 红黑树的主要作用是进行ep_find操作, 62 | * 用户快速查找事件是否已监听, 或快速的修改监听事件的状态集 */ 63 | ep->rbr = RB_ROOT; 64 | 65 | /* ovflist初始化, ovflist将在内核触发通知和epoll_wait中说明*/ 66 | ep->ovflist = EP_UNACTIVE_PTR; 67 | 68 | /* 创建epoll的用户结构体*/ 69 | ep->user = user; 70 | 71 | *pep = ep; 72 | ...... 73 | 74 | free_uid: 75 | /*释放引用计数,当引用为0时, 释放该结构, 此处不讨论*/ 76 | free_uid(user); 77 | ...... 78 | } 79 | 80 | 简单分析下anon_inode_getfd函数 81 | int anon_inode_getfd(const char *name, const struct file_operations *fops, 82 | void *priv, int flags) 83 | { 84 | ...... 85 | 86 | /*申请一个可用的fd descriptor结构, 此处不对此做讨论*/ 87 | error = get_unused_fd_flags(flags); 88 | int fd = error; 89 | 90 | /* 申请一个struct file结构和struct dentry结构 */ 91 | file = anon_inode_getfile(name, fops, priv, flags); 92 | 93 | /*将申请的file结构体存储在对应的fd表中*/ 94 | fd_install(fd, file); 95 | 96 | ...... 97 | } 98 | 99 | 函数anon_inode_getfile 100 | struct file *anon_inode_getfile(const char *name, 101 | const struct file_operations *fops, 102 | void *priv, int flags) 103 | { 104 | struct dentry *dentry; 105 | struct file *file; 106 | 107 | ....... 108 | 109 | dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this); 110 | 111 | /*此处使用了anon_inode_inode结构, 该结构为struct inode结构体, 引用计数加1*/ 112 | atomic_inc(&anon_inode_inode->i_count); 113 | 114 | /*将对应的dentry 添加到anon_inode_inode结构中去*/ 115 | d_instantiate(dentry, anon_inode_inode); 116 | 117 | file = alloc_file(anon_inode_mnt, dentry, 118 | FMODE_READ | FMODE_WRITE, fops); 119 | 120 | file->f_mapping = anon_inode_inode->i_mapping; 121 | file->f_pos = 0; 122 | file->f_flags = O_RDWR | (flags & O_NONBLOCK); 123 | file->f_version = 0; 124 | /*将之前开辟的ep(struct eventpoll 结构体)加入到了该file的私有数据结构中*/ 125 | file->private_data = priv; 126 | 127 | ...... 128 | } 129 | 130 | fd_install函数 131 | void fd_install(unsigned int fd, struct file *file) 132 | { 133 | struct files_struct *files = current->files; 134 | struct fdtable *fdt; 135 | 136 | /*fd descriptor表*/ 137 | fdt = files_fdtable(files); 138 | /*将对应的struct file结构体指针插入到fd表中*/ 139 | rcu_assign_pointer(fdt->fd[fd], file); 140 | } 141 | 142 | epoll_create系统调用主要作用就是创建了一个eventpoll全局结构, 并将在epoll_ctl和epoll_wait中起作用. 143 | -------------------------------------------------------------------------------- /epoll_ctl分析: -------------------------------------------------------------------------------- 1 | |******************************************************************| 2 | |***** epoll_ctl ************| 3 | |******************************************************************| 4 | epoll_ctl主要是将其他的需要监听的套接字加入到epoll_create创建的监听事件中去 5 | 针对在epoll_ctl函数中添加的套接字类型是否具有poll函数指针一说, 可在下面进行分析. 6 | static int sock_attach_fd(struct socket *sock, struct file *file, int flags) 7 | { 8 | ...... 9 | 10 | /*此处使用了socket_file_ops结构体,该结构体就可以使用epoll和poll函数*/ 11 | init_file(file, sock_mnt, dentry, FMODE_READ | FMODE_WRITE, 12 | &socket_file_ops); 13 | SOCK_INODE(sock)->i_fop = &socket_file_ops; 14 | 15 | ...... 16 | } 17 | 18 | 以上的sock_attach_fd是在socket系统调用源码中调用的, 此处赋值的是socket_file_ops结构体, socket_file_ops结构体如下： 19 | static const struct file_operations socket_file_ops = { 20 | ...... 21 | 22 | .poll = sock_poll, 23 | 24 | ...... 25 | }; 26 | 在该结构体中对poll函数进行了赋值, 既为sock_poll. 由此看出socket生成的fd是可以正常添加进epoll_ctl函数中的. 27 | 而在系统调用open中,调用__dentry_open函数. 28 | static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt, 29 | int flags, struct file *f, 30 | int (*open)(struct inode *, struct file *), 31 | const struct cred *cred) 32 | { 33 | ...... 34 | 35 | /*file结构体中的f_op是从inode结构体中的i_fop元素赋值过来的,inode结构中的i_fop一般跟文件系统类型相关*/ 36 | f->f_op = fops_get(inode->i_fop); 37 | 38 | ...... 39 | } 40 | 以ext3文件系统为例, ext3的file_operations结构体如下 41 | const struct file_operations ext3_file_operations = { 42 | .llseek = generic_file_llseek, 43 | .read = do_sync_read, 44 | .write = do_sync_write, 45 | .aio_read = generic_file_aio_read, 46 | .aio_write = generic_file_aio_write, 47 | .unlocked_ioctl = ext3_ioctl, 48 | #ifdef CONFIG_COMPAT 49 | .compat_ioctl = ext3_compat_ioctl, 50 | #endif 51 | .mmap = generic_file_mmap, 52 | .open = generic_file_open, 53 | .release = ext3_release_file, 54 | .fsync = ext3_sync_file, 55 | .splice_read = generic_file_splice_read, 56 | .splice_write = generic_file_splice_write, 57 | }; 58 | 该结构体中没有poll函数的支持,则一般的open产生的跟具体磁盘inode相关的fd描述符是不能添加进epoll_ctl中的. 59 | 60 | 接下来正式分析epoll_ctl函数. 61 | SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, 62 | struct epoll_event __user *, event) 63 | { 64 | struct file *file, *tfile; 65 | struct eventpoll *ep; 66 | struct epitem *epi; 67 | struct epoll_event epds; 68 | 69 | /*ep_op_has_event里面主要用来判断op类型是否为EPOLL_CTL_DEL 70 | 要是delete类型的话, 就不用对参数epoll_event进行拷贝了,否则需要拷贝到内核结构体中*/ 71 | if (ep_op_has_event(op) && 72 | copy_from_user(&epds, event, sizeof(struct epoll_event))) 73 | ....... 74 | 75 | /* 从epoll_create创建的fd中, 获取其对应的file结构体 */ 76 | file = fget(epfd); 77 | ...... 78 | 79 | /*拿到参数中传入的添加fd对应的file结构体*/ 80 | tfile = fget(fd); 81 | 82 | /*判断该file类型是否有f_op操作, 同时是否是具有poll函数, 对于普通的文件套接字, 在此处报错*/ 83 | if (!tfile->f_op || !tfile->f_op->poll) 84 | goto ...... 85 | 86 | /* 如果加入到主监听fd(epoll_create创建的)中的是他本身, 则加入失败 */ 87 | if (file == tfile || !is_file_epoll(file)) 88 | goto ....... 89 | 90 | /*拿到eventpoll结构体*/ 91 | ep = file->private_data; 92 | 93 | /*在红黑树中查找即将监听的fd, 看是否已经存在*/ 94 | epi = ep_find(ep, tfile, fd); 95 | 96 | switch (op) { 97 | case EPOLL_CTL_ADD: 98 | /*如果已经存在, 并且操作时添加操作, 就不用再添加到红黑树中了*/ 99 | if (!epi) { 100 | epds.events |= POLLERR | POLLHUP; 101 | /*不存在的的时候执行插入红黑树的操作*/ 102 | error = ep_insert(ep, &epds, tfile, fd); 103 | } else 104 | error = -EEXIST; 105 | break; 106 | case EPOLL_CTL_DEL: 107 | /*如果是删除操作, 红黑树中已经存在, 则直接进行删除*/ 108 | if (epi) 109 | error = ep_remove(ep, epi); 110 | /*不存在于红黑树中, 无需进行删除*/ 111 | else 112 | error = -ENOENT; 113 | break; 114 | case EPOLL_CTL_MOD: 115 | /*如果已经存在, 则进行更改*/ 116 | if (epi) { 117 | epds.events |= POLLERR | POLLHUP; 118 | error = ep_modify(ep, epi, &epds); 119 | } else 120 | error = -ENOENT; 121 | break; 122 | } 123 | 124 | ...... 125 | } 126 | 127 | 传递给ep_find函数的第二个参数是待监听的fd的file结构体指针, 第三个参数是待监听的fd. 128 | 其中ep_find中主要涉及到的结构体如下: 129 | struct epoll_filefd { 130 | struct file *file; 131 | int fd; 132 | }; 133 | 134 | /*红黑树的节点*/ 135 | struct rb_node 136 | { 137 | unsigned long rb_parent_color; 138 | #define RB_RED 0 139 | #define RB_BLACK 1 140 | struct rb_node *rb_right;/*左孩子指针*/ 141 | struct rb_node *rb_left;/*右孩子指针*/ 142 | } __attribute__((aligned(sizeof(long)))); 143 | 144 | /*红黑树的根节点*/ 145 | struct rb_root 146 | { 147 | struct rb_node *rb_node; 148 | }; 149 | 150 | ep_find主要用来查找当前插入的fd套接字是否已经在epoll监听的红黑树中. 151 | static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) 152 | { 153 | int kcmp; 154 | struct rb_node *rbp; 155 | struct epitem *epi, *epir = NULL; 156 | struct epoll_filefd ffd; 157 | 158 | ep_set_ffd(&ffd, file, fd); 159 | /*遍历红黑树,*/ 160 | for (rbp = ep->rbr.rb_node; rbp; ) { 161 | epi = rb_entry(rbp, struct epitem, rbn); 162 | /*红黑树中的比较函数, 以file结构体指针和fd大小进行比较*/ 163 | kcmp = ep_cmp_ffd(&ffd, &epi->ffd); 164 | if (kcmp > 0) 165 | rbp = rbp->rb_right; 166 | else if (kcmp < 0) 167 | rbp = rbp->rb_left; 168 | else { 169 | /*在红黑树中找到了要插入的fd套接字*/ 170 | epir = epi; 171 | break; 172 | } 173 | } 174 | 175 | return epir; 176 | } 177 | 178 | 179 | ep_insert是插入操作, 插入操作主要是将事件epi插入到红黑树一份, 用于快速查找. 180 | 同时插入到每个套接字的sk_sleep中一份, 用于套接字数据到来时候, 进行通知. 181 | static int ep_insert(struct eventpoll *ep, struct epoll_event *event, 182 | struct file *tfile, int fd) 183 | { 184 | ...... 185 | 186 | 将函数地址ep_ptable_queue_proc赋值给epq(struct ep_pqueue)中的函数指针, 该函数指针主要在下面的f_op->poll中调用. 187 | init_poll_funcptr(&epq.pt, ep_ptable_queue_proc); 188 | 189 | 运行tfile->f_op->poll函数, 返回当前待插入的事件对应的套接字的状态集. 190 | f_op->poll主要调用了sock_poll函数. 191 | sock_poll函数主要调用了sock->ops->poll函数. 192 | sock->ops->poll函数根据不同的协议有对应的函数. 193 | 以tcp_poll函数为例: 194 | ----------------------------------------------------------- 195 | tcp_poll{ 196 | 197 | 调用了上文init_poll_funcptr中赋值进去的ep_ptable_queue_proc函数. 198 | ep_ptable_queue_proc函数是内核触发功能的核心函数, 199 | 该函数将加入epoll监听中的事件挂载到了对应的网络套接字的sk_sleep上. 200 | sock_poll_wait(file, sk->sk_sleep, wait); 201 | 202 | ---------------------------------------------------------------- 203 | ep_ptable_queue_proc{ 204 | 挂载到sk_sleep上的节点结构 205 | struct eppoll_entry *pwq; 206 | 207 | ...... 208 | 209 | 给wait_queue_t结构中的func函数指针赋值, ep_poll_callback将会在内核触发的时候使用. 210 | ep_poll_callback函数的分析在内核触发那块进行. 211 | init_waitqueue_func_entry(&pwq->wait, ep_poll_callback); 212 | 213 | 针对eppoll_entry各种初始化 214 | pwq->whead = whead; 215 | pwq->base = epi; 216 | 217 | 此处的whead是通过ep_ptable_queue_proc参数传递进来的, 实参既为sock结构中的sk_sleep元素. 218 | 这里将套接字结构与监听事件联系在了一起. 219 | add_wait_queue(whead, &pwq->wait); 220 | 221 | ...... 222 | 223 | 将poll使用的eppoll_entry结构挂在到epi的pwqlist元素上 224 | list_add_tail(&pwq->llink, &epi->pwqlist); 225 | epi->nwait++; 226 | 227 | ...... 228 | } 229 | ---------------------------------------------------------------- 230 | 231 | 接下来就是获取当前套机子的状态, 此处不做分析 232 | ....... 233 | } 234 | ----------------------------------------------------------- 235 | revents = tfile->f_op->poll(tfile, &epq.pt); 236 | 237 | 将当前epi事件插入到红黑树中. 238 | ep_rbtree_insert(ep, epi); 239 | 240 | ...... 241 | 242 | 如果刚刚通过epoll_ctl插入的事件已经满足条件(就绪) 243 | if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) { 244 | 245 | 将该事件挂载到eventpoll的就绪事件链表中去, 供epoll_wait使用. 246 | list_add_tail(&epi->rdllink, &ep->rdllist); 247 | 248 | 如果此时已经有epoll_wait在监听该eventpoll, 并处于沉睡状态. 249 | 则调用ep->wq上注册的default_wake_function函数进行epoll_wait唤醒, 250 | 让epoll_wait继续执行for(;;)循环, 关于default_wake_function的说明在内核触发上也有提到. 251 | if (waitqueue_active(&ep->wq)) 252 | wake_up_locked(&ep->wq); 253 | 254 | ...... 255 | } 256 | 257 | ...... 258 | 259 | 要是当前epi事件已经挂在到了eventpoll的rdllist上, 则进行剥离, 避免重复挂载. 260 | if (ep_is_linked(&epi->rdllink)) 261 | list_del_init(&epi->rdllink); 262 | 263 | } 264 | 265 | ep_remove和ep_modify操作和插入操作大同小异, 此处不只做具体分析. 266 | 其中ep_modify更改了事件状态之后, 会即刻唤醒沉睡的epoll_wait函数. 267 | 268 | 269 | 270 | 271 | 272 | 273 | 274 | 275 | -------------------------------------------------------------------------------- /epoll_wait分析: -------------------------------------------------------------------------------- 1 | 2 | ******************************************************************** 3 | ***** epoll_wait ***** 4 | ******************************************************************** 5 | epoll_wait系统调用的入口函数既为YSCALL_DEFINE4(epoll_wait, ...... 6 | 7 | YSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, 8 | int, maxevents, int, timeout) 9 | { 10 | ...... 11 | 判断传递进来的epfd是否是epoll_create函数创建的, epoll_wait只处理epoll_create创建的. 12 | if (!is_file_epoll(file)) 13 | goto error_fput; 14 | 15 | 接下来调用ep_poll函数. 16 | ep_poll(ep, events, maxevents, timeout) 17 | 18 | ...... 19 | } 20 | 21 | 22 | static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 23 | int maxevents, long timeout) 24 | { 25 | ...... 26 | 27 | 针对每个epoll_wait初始化一个wait(wait_queue_t)结构,并将其flags设置为WQ_FLAG_EXCLUSIVE. 28 | WQ_FLAG_EXCLUSIVE标记主要用于内核惊群唤醒时使用, 具体配合使用见内核触发分析. 29 | init_waitqueue_entry(&wait, current); 30 | wait.flags |= WQ_FLAG_EXCLUSIVE; 31 | 32 | 将wait(wait_queue_t结构)加入到eventpoll的wq链表元素上, 主要在内核唤醒时使用 33 | __add_wait_queue(&ep->wq, &wait) 34 | 35 | for (;;) { 36 | 37 | 设置当前睡眠的task_struct 可以被打断 38 | set_current_state(TASK_INTERRUPTIBLE); 39 | 40 | 如果当前eventpoll事件上的监听事件已经就绪或者监听已经超时, 41 | 则跳出循环. 42 | ep->rdllist的就绪节点是内核在数据到来时,执行触发的时候加入的. 43 | if (!list_empty(&ep->rdllist) || !jtimeout) 44 | break; 45 | 46 | 检查是否有信号需要处理 47 | if (signal_pending(current)) { 48 | res = -EINTR; 49 | break; 50 | } 51 | 52 | 进入延时唤醒状态, 让出cpu, 同时会对jtimeout进行减法操作. 53 | jtimeout = schedule_timeout(jtimeout); 54 | } 55 | 56 | 事件来临时, 跳出for(;;)循环后从链表上删除wait 57 | __remove_wait_queue(&ep->wq, &wait); 58 | 59 | ...... 60 | 61 | epoll_wait进程唤醒后, 设置task标记为running态 62 | set_current_state(TASK_RUNNING); 63 | 64 | 调用ep_send_events函数,将就绪的event拷贝到用户态的events数组中来. 65 | 返回的时数据就绪的event事件数. 66 | res = ep_send_events(ep, events, maxevents) 67 | return res; 68 | } 69 | 70 | 71 | static int ep_send_events(struct eventpoll *ep, 72 | struct epoll_event __user *events, int maxevents) 73 | { 74 | struct ep_send_events_data esed; 75 | esed.maxevents = maxevents; 76 | esed.events = events; 77 | 调用 ep_scan_ready_list函数 78 | return ep_scan_ready_list(ep, ep_send_events_proc, &esed); 79 | } 80 | 81 | 82 | static int ep_scan_ready_list(struct eventpoll *ep, 83 | int (*sproc)(struct eventpoll *, 84 | struct list_head *, void *), 85 | void *priv) 86 | { 87 | 将就绪事件的链表转移给txlist. 88 | list_splice_init(&ep->rdllist, &txlist); 89 | 90 | ...... 91 | 92 | 将ep的ovflist从初始化的EP_UNACTIVE_PTR变为NULL. 93 | 因为在sproc函数调用中要对rdllist链表进行遍历, 94 | 并实现从内核态向用户态的拷贝操作,更改ovflist的值, 95 | 并配合内核触发部分,实现类似锁的保护. 96 | ep->ovflist = NULL; 97 | 98 | 执行sproc传入的回调函数, 既调用ep_send_events_proc函数, 在下面进行了该函数分析. 99 | error = (*sproc)(ep, &txlist, priv) 100 | 101 | 当执行sproc进行内核态向用户态的拷贝时, ep的rdllist链表是不允许插入的. 102 | 此时内核触发部分会将满足条件的epi事件插入到ovflist中. 103 | 下面则是将ovflist链表上的部分加入到eventpoll的rdllist上,并做稍后处理. 104 | for (nepi = ep->ovflist; (epi = nepi) != NULL; 105 | nepi = epi->next, epi->next = EP_UNACTIVE_PTR) { 106 | if (!ep_is_linked(&epi->rdllink)) 107 | list_add_tail(&epi->rdllink, &ep->rdllist); 108 | } 109 | 110 | 拷贝操作结束, 将ep->ovflist的值还原为初始化值 111 | ep->ovflist = EP_UNACTIVE_PTR; 112 | 113 | 将sproc中未完全剥离的剩余链表上的epi事件加入到rdllist上. 114 | list_splice(&txlist, &ep->rdllist); 115 | 116 | 如果ep->rdllist上还有节点数据, 有可能是ovflist上拷贝过来的, 117 | 有可能是txlist上剩余的, 也有可能是使用LT模式重新挂载过来的等, 118 | 则进行进程唤醒操作, 既让epoll_wait重新执行起来,将rdllist上的数据进行及时处理. 119 | if (!list_empty(&ep->rdllist)) { 120 | if (waitqueue_active(&ep->wq)) 121 | wake_up_locked(&ep->wq); 122 | ...... 123 | } 124 | 125 | ...... 126 | } 127 | 128 | tatic int ep_send_events_proc(struct eventpoll *ep, struct list_head *head, 129 | void *priv) 130 | { 131 | 其中priv指向了传递进来的struct ep_send_events_data结构. 132 | ...... 133 | 134 | 遍历head链表, 将就绪的事件以此拷贝到esed结构中. 135 | for (eventcnt = 0, uevent = esed->events; 136 | !list_empty(head) && eventcnt < esed->maxevents;) { 137 | 138 | 从链表上依次取下每个节点结构 139 | epi = list_first_entry(head, struct epitem, rdllink); 140 | 141 | 将该节点从链表上进行剥离 142 | list_del_init(&epi->rdllink); 143 | 144 | 返回当前套接字的event状态, 此处不进行具体分析. 145 | 在epoll_ctl函数中也调用了poll函数. 146 | revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL) & 147 | epi->event.events; 148 | 149 | if (revents) { 150 | 如果从内核态向用户态拷贝失败, 则将剥离下来的epi事件重新加入到txlist中. 151 | if (__put_user(revents, &uevent->events) || 152 | __put_user(epi->event.data, &uevent->data)) { 153 | list_add(&epi->rdllink, head); 154 | return eventcnt ? eventcnt : -EFAULT; 155 | } 156 | eventcnt++; 157 | uevent++; 158 | 159 | 当监听的event事件类型中加入了EPOLLONESHOT态, 160 | 既除去了EPOLLIN或者EPOLLOUT等基本类型, 内核就不会进行第二次触发. 161 | 相见内核触发分析. 162 | if (epi->event.events & EPOLLONESHOT) 163 | epi->event.events &= EP_PRIVATE_BITS; 164 | 165 | 当监听的event事件类型中没有加入EPOLLET类型, 166 | 则将该事件继续添加到ep的rdllist中. 167 | else if (!(epi->event.events & EPOLLET)) { 168 | list_add_tail(&epi->rdllink, &ep->rdllist); 169 | } 170 | } 171 | } 172 | 173 | ...... 174 | } 175 | 176 | 177 | 178 | -------------------------------------------------------------------------------- /内核触发通知部分分析: -------------------------------------------------------------------------------- 1 | 2 | ******************************************************************** 3 | ***** 内核触发入口 ***** 4 | ******************************************************************** 5 | 6 | epoll机制是通过内核唤醒来进行触发的, 其基本的操作函数主要是sock_def_readable和sock_def_write_space. 7 | 其中sock_def_readable是EPOLLIN的触发入口,sock_def_write_space是EPOLLOUT的触发入口. 8 | 9 | 一般当有数据到来时候会执行sock_def_readable函数, 10 | 缓冲区有空间可写入时候会执行sock_def_write_space函数, 11 | 此处不对函数调用上下文进行分析. 12 | 13 | sock_def_readble 14 | { 15 | sk_has_sleeper(sk); 16 | 其中的sk_has_sleeper函数主要用来判断当前sock套接字结构中的sk_sleep元素上是否有具体的挂载节点. 17 | 挂载点结构为wait_queue_head_t结构, 其中的task_list(struct list_head)为真正的挂载点. 18 | 挂载chain上的节点结构为eppoll_entry结构, 19 | 其钩子为内部元素wait(wait_queue_t结构),eppoll_entry中存储有元素base(struct epitem结构). 20 | 每个挂载点都可以查找到对应的已加入的监听事件, 具体挂载操作在epoll_ctl函数中. 21 | ...... 22 | wake_up_interruptible_sync_poll --> 宏定义 __wake_up_sync_key 23 | ...... 24 | } 25 | 26 | __wake_up_sync_key 27 | { 28 | 调用了__wake_up_common函数 29 | } 30 | 31 | __wake_up_common 32 | { 33 | 遍历sock结构中的sk_sleep上的task_list循环链表, 当当前的套接字缓冲区有数据时,需要遍历注册到该sk_sleep上的 34 | 所有的监听事件. 35 | 36 | list_for_each_entry_safe(curr, next, &q->task_list, task_list) { 37 | 38 | 执行每一个wait_queue_t结构中的func函数, func函数也是在epoll_ctl中进行初始化的. 39 | 此处的func函数对应的函数为ep_poll_callback, 当func函数为default_wake_function时, 40 | WQ_FLAG_EXCLUSIVE可用于内核防止wake惊群使用.此处的func函数对应ep_poll_callback. 41 | 做惊群使用时, 每个epoll_wait的时候, 会生成一个wait结构, 挂载到ep->wq链表上. 42 | 既多个epoll_wait共同进行时,ep->wq会挂在多个节点, 43 | 但是wake唤醒的时候遇到WQ_FLAG_EXCLUSIVE标记退出, 则只唤醒了第一个. 44 | if (curr->func(curr, mode, wake_flags, key) && 45 | (flags & WQ_FLAG_EXCLUSIVE) && 46 | !--nr_exclusive) 47 | } 48 | } 49 | 50 | curr->func是在ep_ptable_queue_proc函数中进行赋值的, 51 | 此处针对ep_ptable_queue_proc函数的调用发生在epoll_ctl中, 具体分析在epoll_ctl函数中进行. 52 | 53 | ep_poll_callback 54 | { 55 | 从sk_sleep上得到每一个wait_queue_t结构, 56 | 从wait_queue_t结构可以得到包含该结构的eppoll_entry结构. 57 | eppoll_entry是由对应的wait_queue_t和epitem结构组成的. 58 | 59 | struct epitem *epi = ep_item_from_wait(wait); 60 | 61 | 如果注册过的epi事件中, 62 | 除了EPOLLONESHOT和EPOLLET等特殊标识之外,没有其他的基础标识如EPOLLOUT和EPOLLIN, 63 | 则直接跳出不对此epi事件进行处理. 64 | if (!(epi->event.events & ~EP_PRIVATE_BITS)) 65 | goto out_unlock; 66 | 67 | 匹配chain上的每一个epitem里面的events类型(EPOLLIN, EPOLLOUT, EPOLLET,EPOLLLT)是否跟key匹配. 68 | key里的类型在此处为POLLIN类型, 当然在sock_def_write_space函数里传递过来的为POLLOUT类型. 69 | if (key && !((unsigned long) key & epi->event.events)) 70 | goto out_unlock; 71 | 72 | 如果此时ep->ovflist的值不是EP_UNACTIVE_PTR, 说明此刻epoll_wait正在调用ep_scan_ready_list, 73 | 而在ep_scan_ready_list中正在进行内核态向用户态的拷贝操作. 74 | 此时不能直接将epi挂在到ep的rdllist上, 暂时性的挂载到ovflist上. 75 | if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) { 76 | if (epi->next == EP_UNACTIVE_PTR) { 77 | epi->next = ep->ovflist; 78 | ep->ovflist = epi; 79 | } 80 | goto out_unlock; 81 | } 82 | 83 | 判断该epi事件的rdllink链表元素是否为空, 为空的时候则将其挂载到eventpoll主监听集上, 供epoll_wait使用. 84 | 要是该事件的rdllink为非空(已经在rdllist上了), 则不进行挂载. 85 | if (!ep_is_linked(&epi->rdllink)) 86 | list_add_tail(&epi->rdllink, &ep->rdllist); 87 | 88 | 当有epoll_wait监听的时候, 会在ep链表上挂载一个wait进程事件, 89 | 当数据到来时候好唤醒沉睡的epoll_wait. 90 | 挂载操作在epoll_wait函数的for(;;)循环之前进行的, 91 | 具体操作在epoll_wait中进行分析. 92 | if (waitqueue_active(&ep->wq)) 93 | wake_up_locked(&ep->wq); 94 | 95 | 其中wake_up_locked也会调用上文中提到的__wake_up_common. 96 | 但此处__wake_up_common函数中调用的curr->func则与上文不同. 97 | ep->wq链表上的节点挂载是在epoll_wait中执行的,在挂载之前对元素func进行了赋值, 98 | 此处调用的是default_wake_function, 该函数主要用于唤醒沉睡的epoll_wait进程,此处不进行具体分析. 99 | 100 | ...... 101 | } 102 | 103 | 104 | sock_def_write_space函数分析基本同sock_def_readable一致, 此处不再进行具体分析. 105 | 106 | --------------------------------------------------------------------------------