static int restore_one_epoll(cpt_object_t *obj,
loff_t pos,
struct cpt_epoll_image *ebuf,
cpt_context_t *ctx)
{
int err = 0;
loff_t endpos;
struct file *file = obj->o_obj;
struct eventpoll *ep;
if (file->f_op != &eventpoll_fops) {
eprintk_ctx("bad epoll file\n");
return -EINVAL;
}
ep = file->private_data;
if (unlikely(ep == NULL)) {
eprintk_ctx("bad epoll device\n");
return -EINVAL;
}
endpos = pos + ebuf->cpt_next;
pos += ebuf->cpt_hdrlen;
while (pos < endpos) {
struct cpt_epoll_file_image efi;
struct epoll_event epds;
cpt_object_t *tobj;
err = rst_get_object(CPT_OBJ_EPOLL_FILE, pos, &efi, ctx);
if (err)
return err;
tobj = lookup_cpt_obj_bypos(CPT_OBJ_FILE, efi.cpt_file, ctx);
if (!tobj) {
eprintk_ctx("epoll file not found\n");
return -EINVAL;
}
epds.events = efi.cpt_events;
epds.data = efi.cpt_data;
mutex_lock(&ep->mtx);
err = ep_insert(ep, &epds, tobj->o_obj, efi.cpt_fd);
if (!err) {
struct epitem *epi;
epi = ep_find(ep, tobj->o_obj, efi.cpt_fd);
if (epi) {
if (efi.cpt_ready) {
unsigned long flags;
spin_lock_irqsave(&ep->lock, flags);
if (list_empty(&epi->rdllink))
list_add_tail(&epi->rdllink, &ep->rdllist);
spin_unlock_irqrestore(&ep->lock, flags);
}
}
}
mutex_unlock(&ep->mtx);
if (err)
break;
pos += efi.cpt_next;
}
return err;
}
/*
* 创建好epollfd后, 接下来我们要往里面添加fd咯
* 来看epoll_ctl
* epfd 就是epollfd
* op ADD,MOD,DEL
* fd 需要监听的描述符
* event 我们关心的events
*/
SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
struct epoll_event __user *, event)
{
int error;
struct file *file, *tfile;
struct eventpoll *ep;
struct epitem *epi;
struct epoll_event epds;
error = -EFAULT;
/*
* 错误处理以及从用户空间将epoll_event结构copy到内核空间.
*/
if (ep_op_has_event(op) &&
copy_from_user(&epds, event, sizeof(struct epoll_event)))
goto error_return;
/* Get the "struct file *" for the eventpoll file */
/* 取得struct file结构, epfd既然是真正的fd, 那么内核空间
* 就会有与之对于的一个struct file结构
* 这个结构在epoll_create1()中, 由函数anon_inode_getfd()分配 */
error = -EBADF;
file = fget(epfd);
if (!file)
goto error_return;
/* Get the "struct file *" for the target file */
/* 我们需要监听的fd, 它当然也有个struct file结构, 上下2个不要搞混了哦 */
tfile = fget(fd);
if (!tfile)
goto error_fput;
/* The target file descriptor must support poll */
error = -EPERM;
/* 如果监听的文件不支持poll, 那就没辙了.
* 你知道什么情况下, 文件会不支持poll吗?
*/
if (!tfile->f_op || !tfile->f_op->poll)
goto error_tgt_fput;
/*
* We have to check that the file structure underneath the file descriptor
* the user passed to us _is_ an eventpoll file. And also we do not permit
* adding an epoll file descriptor inside itself.
*/
error = -EINVAL;
/* epoll不能自己监听自己... */
if (file == tfile || !is_file_epoll(file))
goto error_tgt_fput;
/*
* At this point it is safe to assume that the "private_data" contains
* our own data structure.
*/
/* 取到我们的eventpoll结构, 来自与epoll_create1()中的分配 */
ep = file->private_data;
/* 接下来的操作有可能修改数据结构内容, 锁之~ */
mutex_lock(&ep->mtx);
/*
* Try to lookup the file inside our RB tree, Since we grabbed "mtx"
* above, we can be sure to be able to use the item looked up by
* ep_find() till we release the mutex.
*/
/* 对于每一个监听的fd, 内核都有分片一个epitem结构,
* 而且我们也知道, epoll是不允许重复添加fd的,
* 所以我们首先查找该fd是不是已经存在了.
* ep_find()其实就是RBTREE查找, 跟C++STL的map差不多一回事, O(lgn)的时间复杂度.
*/
epi = ep_find(ep, tfile, fd);
error = -EINVAL;
switch (op) {
/* 首先我们关心添加 */
case EPOLL_CTL_ADD:
if (!epi) {
/* 之前的find没有找到有效的epitem, 证明是第一次插入, 接受!
* 这里我们可以知道, POLLERR和POLLHUP事件内核总是会关心的
* */
epds.events |= POLLERR | POLLHUP;
/* rbtree插入, 详情见ep_insert()的分析
* 其实我觉得这里有insert的话, 之前的find应该
* 是可以省掉的... */
error = ep_insert(ep, &epds, tfile, fd);
} else
/* 找到了!? 重复添加! */
error = -EEXIST;
break;
/* 删除和修改操作都比较简单 */
case EPOLL_CTL_DEL:
if (epi)
error = ep_remove(ep, epi);
else
error = -ENOENT;
break;
case EPOLL_CTL_MOD:
if (epi) {
epds.events |= POLLERR | POLLHUP;
error = ep_modify(ep, epi, &epds);
} else
error = -ENOENT;
break;
}
mutex_unlock(&ep->mtx);
error_tgt_fput:
fput(tfile);
error_fput:
fput(file);
error_return:
return error;
}
