Linux驱动修炼之道-INPUT子系统(下)

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努力成为linux kernel hacker的人李万鹏原创作品，为梦而战。转载请标明出处

http://blog.csdn.net/woshixingaaa/archive/2011/05/19/6433337.aspx

input子系统最重要的部分就是向上层report了。这里还是先介绍几个数据结构：

struct input_event { struct timeval time; //事件发生的时间 __u16 type; //事件类型 __u16 code; //子事件 __s32 value; //事件的value };

struct evdev_client { struct input_event buffer[EVDEV_BUFFER_SIZE]; //可以同时管理EVDEV_BUFFER_SIZE(64)个事件 int head; //存储事件从head开始 int tail; //取出事件从tail开始 spinlock_t buffer_lock; /* protects access to buffer, head and tail */ struct fasync_struct *fasync; //异步通知事件发生 struct evdev *evdev; //指向本evdev_client归属的evdev struct list_head node; //用于挂载到evdev的链表头client_list上 };

static struct input_handler evdev_handler = { .event = evdev_event, .connect = evdev_connect, .disconnect = evdev_disconnect, .fops = &evdev_fops, .minor = EVDEV_MINOR_BASE, .name = "evdev", .id_table = evdev_ids, };

这里的次设备号是EVDEV_MINOR_BASE(64)，也就是说evdev_handler所表示的设备文件范围(13,64)~(13,64+32)。
如下一个结构体:evdev_handler匹配所有设备。

static const struct input_device_id evdev_ids[] = { { .driver_info = 1 }, /* Matches all devices */ { }, /* Terminating zero entry */ };

这个是evdev_handler是fops，下面的讲解中会用到其中的open,read函数。

static const struct file_operations evdev_fops = { .owner = THIS_MODULE, .read = evdev_read, .write = evdev_write, .poll = evdev_poll, .open = evdev_open, .release = evdev_release, .unlocked_ioctl = evdev_ioctl, #ifdef CONFIG_COMPAT .compat_ioctl = evdev_ioctl_compat, #endif .fasync = evdev_fasync, .flush = evdev_flush };

在驱动程序中我们会调用input_report_abs等函数：

static inline void input_report_abs(struct input_dev *dev, unsigned int code, int value) { input_event(dev, EV_ABS, code, value); }

跟踪input_event如下：

void input_event(struct input_dev *dev, unsigned int type, unsigned int code, int value) { unsigned long flags; if (is_event_supported(type, dev->evbit, EV_MAX)) { spin_lock_irqsave(&dev->event_lock, flags); /*利用输入值调正随机数产生器*/ add_input_randomness(type, code, value); input_handle_event(dev, type, code, value); spin_unlock_irqrestore(&dev->event_lock, flags); } }

跟踪input_handle_event如下：

static void input_handle_event(struct input_dev *dev, unsigned int type, unsigned int code, int value) { int disposition = INPUT_IGNORE_EVENT; switch (type) { 。。。。。。。。。。。。。。。。 if (disposition != INPUT_IGNORE_EVENT && type != EV_SYN) dev->sync = 0; if ((disposition & INPUT_PASS_TO_DEVICE) && dev->event) dev->event(dev, type, code, value); if (disposition & INPUT_PASS_TO_HANDLERS) input_pass_event(dev, type, code, value); }

如果该事件需要input device来完成，就会将disposition设置成INPUT_PASS_TO_DEVICE，如果需要input handler来完成，就会将disposition设置成INPUT_PASS_TO_DEVICE，如果需要两者都参与，则将disposition设置成INPUT_PASS_TO_ALL。
跟踪input_pass_event如下：

static void input_pass_event(struct input_dev *dev, unsigned int type, unsigned int code, int value) { struct input_handle *handle; rcu_read_lock(); /**/ handle = rcu_dereference(dev->grab); if (handle) /*如果input_dev的grab指向了一个handle，就用这个handle关联的handler的event，否则遍历整个挂在input_dev的h_list上的handle关联的handler*/ handle->handler->event(handle, type, code, value); else list_for_each_entry_rcu(handle, &dev->h_list, d_node) if (handle->open) handle->handler->event(handle, type, code, value); rcu_read_unlock(); }

比如下边的evdev_handler的evdev_event：

static void evdev_event(struct input_handle *handle, unsigned int type, unsigned int code, int value) { struct evdev *evdev = handle->private; struct evdev_client *client; struct input_event event; do_gettimeofday(&event.time); event.type = type; event.code = code; event.value = value; rcu_read_lock(); client = rcu_dereference(evdev->grab); if (client) /*如果evdev->grab指向一个当前使用的client就将event放到这个client的buffer中，否则放到整个client_list上的client的链表中*/ evdev_pass_event(client, &event); else list_for_each_entry_rcu(client, &evdev->client_list, node) evdev_pass_event(client, &event); rcu_read_unlock(); wake_up_interruptible(&evdev->wait); }

static void evdev_pass_event(struct evdev_client *client, struct input_event *event) { /* * Interrupts are disabled, just acquire the lock */ spin_lock(&client->buffer_lock); /*将event装入client的buffer中，buffer是一个环形缓存区*/ client->buffer[client->head++] = *event; client->head &= EVDEV_BUFFER_SIZE - 1; spin_unlock(&client->buffer_lock); kill_fasync(&client->fasync, SIGIO, POLL_IN); }

这里总结一下事件的传递过程：首先在驱动层中，调用inport_report_abs，然后他调用了input core层的input_event，input_event调用了input_handle_event对事件进行分派，调用input_pass_event，在这里他会把事件传递给具体的handler层，然后在相应handler的event处理函数中，封装一个event，然后把它投入evdev的那个client_list上的client的事件buffer中，等待用户空间来读取。

当用户空间打开设备节点/dev/input/event0~/dev/input/event4的时候，会使用input_fops中的input_open_file()函数，input_open_file()->evdev_open()(如果handler是evdev的话)->evdev_open_device()->input_open_device()->dev->open()。也就是struct file_operations input_fops提供了通用接口，最终会调用具体input_dev的open函数。下边看一下用户程序打开文件时的过程，首先调用了input_open_file:

static int input_open_file(struct inode *inode, struct file *file) { struct input_handler *handler; const struct file_operations *old_fops, *new_fops = NULL; int err; lock_kernel(); /* No load-on-demand here? */ /*因为32个input_dev公共一个handler所以低5位应该是相同的*/ handler = input_table[iminor(inode) >> 5]; if (!handler || !(new_fops = fops_get(handler->fops))) { err = -ENODEV; goto out; } /* * That's _really_ odd. Usually NULL ->open means "nothing special", * not "no device". Oh, well... */ if (!new_fops->open) { fops_put(new_fops); err = -ENODEV; goto out; } /*保存以前的fops，使用相应的handler的fops*/ old_fops = file->f_op; file->f_op = new_fops; err = new_fops->open(inode, file); if (err) { fops_put(file->f_op); file->f_op = fops_get(old_fops); } fops_put(old_fops); out: unlock_kernel(); return err; }

这里还是假设handler是evdev_handler。

static int evdev_open(struct inode *inode, struct file *file) { struct evdev *evdev; struct evdev_client *client; /*因为次设备号是从EVDEV_MINOR_BASE开始的*/ int i = iminor(inode) - EVDEV_MINOR_BASE; int error; if (i >= EVDEV_MINORS) return -ENODEV; error = mutex_lock_interruptible(&evdev_table_mutex); if (error) return error; /*evdev_table一共可容纳32个成员，找到次设备号对应的那个*/ evdev = evdev_table[i]; if (evdev) get_device(&evdev->dev); mutex_unlock(&evdev_table_mutex); if (!evdev) return -ENODEV; /*打开的时候创建一个client*/ client = kzalloc(sizeof(struct evdev_client), GFP_KERNEL); if (!client) { error = -ENOMEM; goto err_put_evdev; } spin_lock_init(&client->buffer_lock); /*下边两句的作用就是将evdev和client绑定到一起*/ client->evdev = evdev; evdev_attach_client(evdev, client); error = evdev_open_device(evdev); if (error) goto err_free_client; /*将file->private_data指向刚刚建的client，后边会用到的*/ file->private_data = client; return 0; err_free_client: evdev_detach_client(evdev, client); kfree(client); err_put_evdev: put_device(&evdev->dev); return error; }

static int evdev_open_device(struct evdev *evdev) { int retval; retval = mutex_lock_interruptible(&evdev->mutex); if (retval) return retval; /*如果设备不存在，返回错误*/ if (!evdev->exist) retval = -ENODEV; /*如果是被第一次打开，则调用input_open_device*/ else if (!evdev->open++) { retval = input_open_device(&evdev->handle); if (retval) evdev->open--; } mutex_unlock(&evdev->mutex); return retval; }

int input_open_device(struct input_handle *handle) { struct input_dev *dev = handle->dev; int retval; retval = mutex_lock_interruptible(&dev->mutex); if (retval) return retval; if (dev->going_away) { retval = -ENODEV; goto out; } handle->open++; if (!dev->users++ && dev->open) retval = dev->open(dev); if (retval) { dev->users--; if (!--handle->open) { /* * Make sure we are not delivering any more events * through this handle */ synchronize_rcu(); } } out: mutex_unlock(&dev->mutex); return retval; }

下面是用户进程读取event的底层实现：

static ssize_t evdev_read(struct file *file, char __user *buffer, size_t count, loff_t *ppos) { /*这个就是刚才在open函数中*/ struct evdev_client *client = file->private_data; struct evdev *evdev = client->evdev; struct input_event event; int retval; if (count < input_event_size()) return -EINVAL; /*如果client的环形缓冲区中没有数据并且是非阻塞的，那么返回-EAGAIN，也就是try again*/ if (client->head == client->tail && evdev->exist && (file->f_flags & O_NONBLOCK)) return -EAGAIN; /*如果没有数据，并且是阻塞的，则在等待队列上等待吧*/ retval = wait_event_interruptible(evdev->wait, client->head != client->tail || !evdev->exist); if (retval) return retval; if (!evdev->exist) return -ENODEV; /*如果获得了数据则取出来，调用evdev_fetch_next_event*/ while (retval + input_event_size() <= count && evdev_fetch_next_event(client, &event)) { /*input_event_to_user调用copy_to_user传入用户程序中，这样读取完成*/ if (input_event_to_user(buffer + retval, &event)) return -EFAULT; retval += input_event_size(); } return retval; }

static int evdev_fetch_next_event(struct evdev_client *client, struct input_event *event) { int have_event; spin_lock_irq(&client->buffer_lock); /*先判断一下是否有数据*/ have_event = client->head != client->tail; /*如果有就从环形缓冲区的取出来，记得是从head存储，tail取出*/ if (have_event) { *event = client->buffer[client->tail++]; client->tail &= EVDEV_BUFFER_SIZE - 1; } spin_unlock_irq(&client->buffer_lock); return have_event; }

int input_event_to_user(char __user *buffer, const struct input_event *event) { /*如果设置了标志INPUT_COMPAT_TEST就将事件event包装成结构体compat_event*/ if (INPUT_COMPAT_TEST) { struct input_event_compat compat_event; compat_event.time.tv_sec = event->time.tv_sec; compat_event.time.tv_usec = event->time.tv_usec; compat_event.type = event->type; compat_event.code = event->code; compat_event.value = event->value; /*将包装成的compat_event拷贝到用户空间*/ if (copy_to_user(buffer, &compat_event, sizeof(struct input_event_compat))) return -EFAULT; } else { /*否则，将event拷贝到用户空间*/ if (copy_to_user(buffer, event, sizeof(struct input_event))) return -EFAULT; } return 0; }

这里总结一下：如果两个进程打开同一个文件，每个进程在打开时都会生成一个evdev_client，evdev_client被挂在evdev的client_list，在handle收到一个事件的时候，会把事件copy到挂在client_list上的所有evdev_client的buffer中。这样所有打开同一个设备的进程都会收到这个消息而唤醒。

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