输入子系统由驱动层、输入子系统核心、事件处理层三部分组成。一个输入事件,如鼠标移动、键盘按下等通过Driver->Inputcore->Event handler->userspace的顺序到达用户控件的应用程序。
假设打开一个字符设备驱动程序/dev/event0,event代表的是输入子系统的设备文件,当应用程序调用C库的open函数后,open函数会进入系统调用,最后定位到drivers\input\input.c文件下(这个文件就是核心层)的。这个函数的功能主要是根据设备的次设备号找到新的fops结构,然后切换到新的fops结构,然后调用它的打开函数。输入子系统的主设备号恒为#define INPUT_MAJOR 13,定义在include\linux\major.h中。
static int input_open_file(struct inode *inode, struct file *file) { struct input_handler *handler = input_table[iminor(inode) >> 5];//根据次设备号找到在input_table表中找到handler结构体 const struct file_operations *old_fops, *new_fops = NULL; int err; /* No load-on-demand here? */ if (!handler || !(new_fops = fops_get(handler->fops)))//判断handler结构体是否存在,存在的话将里面的fops变量赋给new_fops return -ENODEV; /* * That's _really_ odd. Usually NULL ->open means "nothing special", * not "no device". Oh, well... */ if (!new_fops->open) { fops_put(new_fops); return -ENODEV; } old_fops = file->f_op; file->f_op = new_fops;//切换f_op变量,以后调用诸如read、write等系统调用时会进入到new_fops的read、write函数 err = new_fops->open(inode, file);//调用new_fops的open函数 if (err) { fops_put(file->f_op); file->f_op = fops_get(old_fops); } fops_put(old_fops);//释放掉老的fops结构 return err; }
接着先来看到input_table表的建立,可以看到它是一个静态变量,在本文件(drivers\input\input.c)中搜索它,可以看到它位于input_register_handler函数,这是一个全局的函数,可以供外部的文件调用,这个函数的主要功能是注册一个handler结构体,这个结构体中存在minor这个设备的次设备号,这个结构所在的函数对应的其实就是上述的事件层。
int input_register_handler(struct input_handler *handler) { struct input_dev *dev; INIT_LIST_HEAD(&handler->h_list);//初始化handler的h_list结构体,这是一个双向链表 if (handler->fops != NULL) { if (input_table[handler->minor >> 5])//检查是否已经存在这个次设备号的handler结构 return -EBUSY; input_table[handler->minor >> 5] = handler;//将handler结构次设备号放入input_table表 } list_add_tail(&handler->node, &input_handler_list);//将handler结构根据node成员放入input_handler_list链表 list_for_each_entry(dev, &input_dev_list, node)//根据node这个成员在input_dev_list链表中循环查找dev结构 input_attach_handler(dev, handler);//对于每一个dev结构调用input_attach_handler函数 input_wakeup_procfs_readers();//将这个设备信息写入proc文件系统 return 0; }
接着搜索input_register_handler,抽取drivers\input\evdev.c这个文件,可以看到在这个模块的入口函数调用了注册函数
static int __init evdev_init(void) { return input_register_handler(&evdev_handler); }
接着看到evdev_handler这个结构体,在这个结构体里面找到了evdev_fops这个结构
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, };
接着看到evdev_fops结构体,可以看到应用层调用的read、write等函数在这里被定义
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 };
知道了事件层对应的位置,那么设备驱动层在哪里呢?接着往下看,回到input_register_handler函数,在里面看到如下语句,这句语句的作用是将事件层与驱动层联系起来。
list_for_each_entry(dev, &input_dev_list, node)//根据node这个成员在input_dev_list链表中循环查找dev结构 input_attach_handler(dev, handler);//对于每一个dev结构调用input_attach_handler函数
这里可以看到一个新的结构体dev,先看一下dev结构体,它的原型为input_dev,跟抽取drivers\input\evdev.c这个文件一样,搜索input_dev这个结构体,先列出input_dev这个结构体
struct input_dev { void *private; const char *name; const char *phys; const char *uniq; struct input_id id; unsigned long evbit[NBITS(EV_MAX)]; unsigned long keybit[NBITS(KEY_MAX)]; unsigned long relbit[NBITS(REL_MAX)]; unsigned long absbit[NBITS(ABS_MAX)]; unsigned long mscbit[NBITS(MSC_MAX)]; unsigned long ledbit[NBITS(LED_MAX)]; unsigned long sndbit[NBITS(SND_MAX)]; unsigned long ffbit[NBITS(FF_MAX)]; unsigned long swbit[NBITS(SW_MAX)]; unsigned int keycodemax; unsigned int keycodesize; void *keycode; int (*setkeycode)(struct input_dev *dev, int scancode, int keycode); int (*getkeycode)(struct input_dev *dev, int scancode, int *keycode); struct ff_device *ff; unsigned int repeat_key; struct timer_list timer; int state; int sync; int abs[ABS_MAX + 1]; int rep[REP_MAX + 1]; unsigned long key[NBITS(KEY_MAX)]; unsigned long led[NBITS(LED_MAX)]; unsigned long snd[NBITS(SND_MAX)]; unsigned long sw[NBITS(SW_MAX)]; int absmax[ABS_MAX + 1]; int absmin[ABS_MAX + 1]; int absfuzz[ABS_MAX + 1]; int absflat[ABS_MAX + 1]; int (*open)(struct input_dev *dev); void (*close)(struct input_dev *dev); int (*flush)(struct input_dev *dev, struct file *file); int (*event)(struct input_dev *dev, unsigned int type, unsigned int code, int value); struct input_handle *grab; struct mutex mutex; /* serializes open and close operations */ unsigned int users; struct class_device cdev; union { /* temporarily so while we switching to struct device */ struct device *parent; } dev; struct list_head h_list; struct list_head node; };
接着看到drivers\input\tablet\kbtab.c这个文件,这个文件代表的就是设备驱动层,简单分析一下,可以看到它也是一个内核的模块,可以动态加载,一旦加载后,它会调用kbtab_init函数,最终会调用到kbtab_probe这个函数,可以看到最终又定位到了input_register_device这个注册设备的函数,它位于核心层,即drivers\input\input.c文件下。
static int kbtab_probe(struct usb_interface *intf, const struct usb_device_id *id) { ... ... input_dev = input_allocate_device();//分配一个input_dev 结构体 if (!kbtab || !input_dev) goto fail1; ... ... input_dev->name = "KB Gear Tablet";//初始化input_dev 结构体 input_dev->phys = kbtab->phys; usb_to_input_id(dev, &input_dev->id); input_dev->dev.parent = &intf->dev; input_set_drvdata(input_dev, kbtab); input_dev->open = kbtab_open; input_dev->close = kbtab_close; input_dev->evbit[0] |= BIT(EV_KEY) | BIT(EV_ABS) | BIT(EV_MSC); input_dev->keybit[LONG(BTN_LEFT)] |= BIT(BTN_LEFT) | BIT(BTN_RIGHT) | BIT(BTN_MIDDLE); input_dev->keybit[LONG(BTN_DIGI)] |= BIT(BTN_TOOL_PEN) | BIT(BTN_TOUCH); input_dev->mscbit[0] |= BIT(MSC_SERIAL); input_set_abs_params(input_dev, ABS_X, 0, 0x2000, 4, 0); input_set_abs_params(input_dev, ABS_Y, 0, 0x1750, 4, 0); input_set_abs_params(input_dev, ABS_PRESSURE, 0, 0xff, 0, 0); ... ... error = input_register_device(kbtab->dev);//注册input_dev结构体 ... ... }
接着看到input_register_device这个函数,它根input_register_handler相对应,前一个注册设备驱动层,后一个注册事件层。列出input_register_device函数,它同样位于drivers\input\input.c文件中。
int input_register_device(struct input_dev *dev) { static atomic_t input_no = ATOMIC_INIT(0); struct input_handler *handler; const char *path; int error; set_bit(EV_SYN, dev->evbit);//设置同步事件 /* * If delay and period are pre-set by the driver, then autorepeating * is handled by the driver itself and we don't do it in input.c. */ init_timer(&dev->timer);//初始化一个定时器 if (!dev->rep[REP_DELAY] && !dev->rep[REP_PERIOD]) {//按键是否需要重复,如果需要设置重复函数与重复时间 dev->timer.data = (long) dev; dev->timer.function = input_repeat_key; dev->rep[REP_DELAY] = 250; dev->rep[REP_PERIOD] = 33; } if (!dev->getkeycode) dev->getkeycode = input_default_getkeycode;//获得按键值默认函数 if (!dev->setkeycode) dev->setkeycode = input_default_setkeycode;//设置按键值默认函数 list_add_tail(&dev->node, &input_dev_list);//将dev->node放入input_dev_list链表 snprintf(dev->cdev.class_id, sizeof(dev->cdev.class_id), "input%ld", (unsigned long) atomic_inc_return(&input_no) - 1); if (!dev->cdev.dev) dev->cdev.dev = dev->dev.parent; error = class_device_add(&dev->cdev); if (error) return error; path = kobject_get_path(&dev->cdev.kobj, GFP_KERNEL); printk(KERN_INFO "input: %s as %s\n", dev->name ? dev->name : "Unspecified device", path ? path : "N/A"); kfree(path); list_for_each_entry(handler, &input_handler_list, node)//根据node这个成员在input_handler_list链表中循环查找handler结构 input_attach_handler(dev, handler);//对于每一个handler结构调用input_attach_handler函数 input_wakeup_procfs_readers();//将这个设备信息写入proc文件系统 return 0; }
可以看到它同样也调用了input_attach_handler函数,将设备驱动层与事件层联系起来。这个函数也位于drivers\input\input.c文件中。它的主要功能是
1、根据handler->id_table的值匹配dev,找到id
2、调用调用handler->connect进行匹配
static int input_attach_handler(struct input_dev *dev, struct input_handler *handler) { const struct input_device_id *id; int error; if (handler->blacklist && input_match_device(handler->blacklist, dev)) return -ENODEV; id = input_match_device(handler->id_table, dev);//根据handler->id_table的值匹配dev,找到id if (!id) return -ENODEV; error = handler->connect(handler, dev, id);//调用handler->connect进行匹配 if (error && error != -ENODEV) printk(KERN_ERR "input: failed to attach handler %s to device %s, " "error: %d\n", handler->name, kobject_name(&dev->cdev.kobj), error); return error; }
接着看到input_match_device函数
static const struct input_device_id *input_match_device(const struct input_device_id *id, struct input_dev *dev) { int i; for (; id->flags || id->driver_info; id++) {//循环查找支持的id if (id->flags & INPUT_DEVICE_ID_MATCH_BUS) if (id->bustype != dev->id.bustype) continue; if (id->flags & INPUT_DEVICE_ID_MATCH_VENDOR) if (id->vendor != dev->id.vendor) continue; if (id->flags & INPUT_DEVICE_ID_MATCH_PRODUCT) if (id->product != dev->id.product) continue; if (id->flags & INPUT_DEVICE_ID_MATCH_VERSION) if (id->version != dev->id.version) continue; MATCH_BIT(evbit, EV_MAX);// MATCH_BIT(keybit, KEY_MAX); MATCH_BIT(relbit, REL_MAX); MATCH_BIT(absbit, ABS_MAX); MATCH_BIT(mscbit, MSC_MAX); MATCH_BIT(ledbit, LED_MAX); MATCH_BIT(sndbit, SND_MAX); MATCH_BIT(ffbit, FF_MAX); MATCH_BIT(swbit, SW_MAX); return id; } return NULL;
再看到handler->connect函数,这里选取的是evdev_handler ->evdev_connect函数,这个函数的主要作用就是将handle、handler、evdev三者相互匹配起来
static int evdev_connect(struct input_handler *handler, struct input_dev *dev, const struct input_device_id *id) { struct evdev *evdev; struct class_device *cdev; dev_t devt; int minor; int error; for (minor = 0; minor < EVDEV_MINORS && evdev_table[minor]; minor++);//取得次设备号,如果还没有利用则evdev_table为空 if (minor == EVDEV_MINORS) { printk(KERN_ERR "evdev: no more free evdev devices\n");//没有剩余的空间可以用了 return -ENFILE; } evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL);//分配一个evdev if (!evdev) return -ENOMEM; INIT_LIST_HEAD(&evdev->client_list); init_waitqueue_head(&evdev->wait); evdev->exist = 1; //evdev初始化 evdev->minor = minor; evdev->handle.dev = dev; //初始化evdev->handle.dev evdev->handle.name = evdev->name; evdev->handle.handler = handler; //初始化evdev->handle.handler evdev->handle.private = evdev; sprintf(evdev->name, "event%d", minor);//打印次设备号,每次注册新的设备驱动都会打印 evdev_table[minor] = evdev;//将分配的evdev放入evdev_table[minor] devt = MKDEV(INPUT_MAJOR, EVDEV_MINOR_BASE + minor), cdev = class_device_create(&input_class, &dev->cdev, devt, dev->cdev.dev, evdev->name);//创建一个字符设备节点 if (IS_ERR(cdev)) { error = PTR_ERR(cdev); goto err_free_evdev; } /* temporary symlink to keep userspace happy */ error = sysfs_create_link(&input_class.subsys.kobj, &cdev->kobj, evdev->name); if (error) goto err_cdev_destroy; /* llist_add_tail(&handle->d_node, &handle->dev->h_list);//将&handle->d_node 放入&handle->dev->h_list链表 list_add_tail(&handle->h_node, &handler->h_list); //将&handle->h_node 放入 &handler->h_list链表? */ error = input_register_handle(&evdev->handle);//注册evdev->handle if (error) goto err_remove_link; return 0; err_remove_link: sysfs_remove_link(&input_class.subsys.kobj, evdev->name); err_cdev_destroy: class_device_destroy(&input_class, devt); err_free_evdev: kfree(evdev); evdev_table[minor] = NULL; return error; }
再回过头来看一下应用层是怎么读取按键值得:应用层调用C库的read函数,通过前面的分析可以知道,最终会通过系统调用会定位到内核的evdev_handler ->fops ->evdev_read,下面看到evdev_read函数,它位于事件层,这个函数根据读取方式的不同采取不同的方式,如果是阻塞方式打开的话最终会当前进程放入等待队列,一直等到有数据才将进程唤醒。
static ssize_t evdev_read(struct file *file, char __user *buffer, size_t count, loff_t *ppos) { struct evdev_client *client = file->private_data; struct evdev *evdev = client->evdev; int retval; if (count < evdev_event_size()) return -EINVAL; if (client->head == client->tail && evdev->exist && (file->f_flags & O_NONBLOCK))//如果采用非阻塞方式读取,并且每天数据直接返回 return -EAGAIN; retval = wait_event_interruptible(evdev->wait, client->head != client->tail || !evdev->exist);//阻塞方式读取,先将当前进程休眠,等待有数据后被唤醒 if (retval) return retval; if (!evdev->exist) return -ENODEV; while (client->head != client->tail && retval + evdev_event_size() <= count) {//头!=尾表示有数据 struct input_event *event = (struct input_event *) client->buffer + client->tail; if (evdev_event_to_user(buffer + retval, event))//将得到的数据考回给用户层 return -EFAULT; client->tail = (client->tail + 1) & (EVDEV_BUFFER_SIZE - 1); retval += evdev_event_size(); } return retval; }
接下来的问题就是谁将进程唤醒,我们直接看到设备驱动层,即drivers\input\tablet\kbtab.c,在这个文件中有一个kbtab_irq函数,它是一个中断处理函数,它位于设备驱动层,负责将中断过来的按键数据上报调用的是input_report_key函数,input_report_key函数最终调用的是input_event函数,他们全部都属于核心层。接着看一下input_event的核心代码
list_for_each_entry(handle, &dev->h_list, d_node)//根据dev设备驱动层的h_list找出handle结构体 if (handle->open) handle->handler->event(handle, type, code, value);//调用事件层的handle->handler->event进行处理
再回过头看事件层的event,即evdev_event函数,可以看到在这个函数里将按键的相关的值取出后,最终进程的唤醒函数在这里调用wake_up_interruptible。
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; if (evdev->grab) { client = evdev->grab; do_gettimeofday(&client->buffer[client->head].time); client->buffer[client->head].type = type; client->buffer[client->head].code = code; client->buffer[client->head].value = value; client->head = (client->head + 1) & (EVDEV_BUFFER_SIZE - 1); kill_fasync(&client->fasync, SIGIO, POLL_IN); } else list_for_each_entry(client, &evdev->client_list, node) { do_gettimeofday(&client->buffer[client->head].time);//时间 8字节 client->buffer[client->head].type = type; //按键类型 2字节 client->buffer[client->head].code = code; //按键码 2字节 client->buffer[client->head].value = value; //按键值,按下或松开 4字节 client->head = (client->head + 1) & (EVDEV_BUFFER_SIZE - 1); kill_fasync(&client->fasync, SIGIO, POLL_IN);//异步通知 } wake_up_interruptible(&evdev->wait);//唤醒进程 }
总结一下整个输入子系统的调用过程:
app_open->input_open_file->evdev_open
应用层 核心层 事件层
app_read->evdev_read->kbtab_irq->input_report_key->input_event->evdev_event->evdev_read
应用层 事件层 设备层 核心层 核心层 事件层 事件层
如果要自己添加一个输入子系统的设备,只需要添加设备层的文件即可。
1、在里面添加设备层input_dev结构并初始化
2、编写中断处理程序