input事件处理流程 input driver -> input core ->event handler -> userspace 给应用程序。
一 事件分发跟踪
核心层留给驱动层的上报接口是input_report_abs(),最终会调用input_event()。
[cpp]
- 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);
- input_handle_event(dev, type, code, value);
- spin_unlock_irqrestore(&dev->event_lock, flags);
- }
- }
-
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); -
input_handle_event(dev, type, code, value); -
spin_unlock_irqrestore(&dev->event_lock, flags); -
} -
}
先判断type是否支持,接着进入处理核心。
[cpp]
- static void input_handle_event(struct input_dev *dev,
- unsigned int type, unsigned int code, int value)
- {
- int disposition;
- disposition = input_get_disposition(dev, type, code, value);
- if ((disposition & INPUT_PASS_TO_DEVICE) && dev->event)
- dev->event(dev, type, code, value);
- if (!dev->vals)
- return;
- if (disposition & INPUT_PASS_TO_HANDLERS) {
- struct input_value *v;
- if (disposition & INPUT_SLOT) {
- v = &dev->vals[dev->num_vals++];
- v->type = EV_ABS;
- v->code = ABS_MT_SLOT;
- v->value = dev->mt->slot;
- }
- v = &dev->vals[dev->num_vals++];
- v->type = type;
- v->code = code;
- v->value = value;
- }
- if (disposition & INPUT_FLUSH) {
- if (dev->num_vals >= 2)
- input_pass_values(dev, dev->vals, dev->num_vals);
- dev->num_vals = 0;
- } else if (dev->num_vals >= dev->max_vals - 2) {
- dev->vals[dev->num_vals++] = input_value_sync;
- input_pass_values(dev, dev->vals, dev->num_vals);
- dev->num_vals = 0;
- }
- }
-
static void input_handle_event(struct input_dev *dev, -
unsigned int type, unsigned int code, int value) -
{ -
int disposition; -
-
disposition = input_get_disposition(dev, type, code, value); -
-
if ((disposition & INPUT_PASS_TO_DEVICE) && dev->event) -
dev->event(dev, type, code, value); -
-
if (!dev->vals) -
return; -
-
if (disposition & INPUT_PASS_TO_HANDLERS) { -
struct input_value *v; -
-
if (disposition & INPUT_SLOT) { -
v = &dev->vals[dev->num_vals++]; -
v->type = EV_ABS; -
v->code = ABS_MT_SLOT; -
v->value = dev->mt->slot; -
} -
-
v = &dev->vals[dev->num_vals++]; -
v->type = type; -
v->code = code; -
v->value = value; -
} -
-
if (disposition & INPUT_FLUSH) { -
if (dev->num_vals >= 2) -
input_pass_values(dev, dev->vals, dev->num_vals); -
dev->num_vals = 0; -
} else if (dev->num_vals >= dev->max_vals - 2) { -
dev->vals[dev->num_vals++] = input_value_sync; -
input_pass_values(dev, dev->vals, dev->num_vals); -
dev->num_vals = 0; -
} -
-
}
input_get_disposition()获得事件处理者身份。INPUT_PASS_TO_HANDLERS表示交给input hardler处理,INPUT_PASS_TO_DEVICE表示交给input device处理,INPUT_FLUSH表示需要handler立即处理。如果事件正常一般返回的是INPUT_PASS_TO_HANDLERS,只有code为SYN_REPORT时返回INPUT_PASS_TO_HANDLERS | INPUT_FLUSH。需要说明的是下面一段:
[cpp]
- case EV_ABS:
- if (is_event_supported(code, dev->absbit, ABS_MAX))
- disposition = input_handle_abs_event(dev, code, &value);
-
case EV_ABS: -
if (is_event_supported(code, dev->absbit, ABS_MAX)) -
disposition = input_handle_abs_event(dev, code, &value);
- static int input_handle_abs_event(struct input_dev *dev,
- unsigned int code, int *pval)
- {
- struct input_mt *mt = dev->mt;
- bool is_mt_event;
- int *pold;
- if (code == ABS_MT_SLOT) {
- /*
- * "Stage" the event; we'll flush it later, when we
- * get actual touch data.
- */
- if (mt && *pval >= 0 && *pval < mt->num_slots)
- mt->slot = *pval;
- return INPUT_IGNORE_EVENT;
- }
- is_mt_event = input_is_mt_value(code);
- if (!is_mt_event) {
- pold = &dev->absinfo[code].value;
- } else if (mt) {
- pold = &mt->slots[mt->slot].abs[code - ABS_MT_FIRST];
- } else {
- /*
- * Bypass filtering for multi-touch events when
- * not employing slots.
- */
- pold = NULL;
- }
- if (pold) {
- *pval = input_defuzz_abs_event(*pval, *pold,
- dev->absinfo[code].fuzz);
- if (*pold == *pval)
- return INPUT_IGNORE_EVENT;
- *pold = *pval;
- }
- /* Flush pending "slot" event */
- if (is_mt_event && mt && mt->slot != input_abs_get_val(dev, ABS_MT_SLOT)) {
- input_abs_set_val(dev, ABS_MT_SLOT, mt->slot);
- return INPUT_PASS_TO_HANDLERS | INPUT_SLOT;
- }
- return INPUT_PASS_TO_HANDLERS;
- }
-
static int input_handle_abs_event(struct input_dev *dev, -
unsigned int code, int *pval) -
{ -
struct input_mt *mt = dev->mt; -
bool is_mt_event; -
int *pold; -
-
if (code == ABS_MT_SLOT) { -
/* -
* "Stage" the event; we'll flush it later, when we -
* get actual touch data. -
*/ -
if (mt && *pval >= 0 && *pval < mt->num_slots) -
mt->slot = *pval; -
-
return INPUT_IGNORE_EVENT; -
} -
-
is_mt_event = input_is_mt_value(code); -
-
if (!is_mt_event) { -
pold = &dev->absinfo[code].value; -
} else if (mt) { -
pold = &mt->slots[mt->slot].abs[code - ABS_MT_FIRST]; -
} else { -
/* -
* Bypass filtering for multi-touch events when -
* not employing slots. -
*/ -
pold = NULL; -
} -
-
if (pold) { -
*pval = input_defuzz_abs_event(*pval, *pold, -
dev->absinfo[code].fuzz); -
if (*pold == *pval) -
return INPUT_IGNORE_EVENT; -
-
*pold = *pval; -
} -
-
/* Flush pending "slot" event */ -
if (is_mt_event && mt && mt->slot != input_abs_get_val(dev, ABS_MT_SLOT)) { -
input_abs_set_val(dev, ABS_MT_SLOT, mt->slot); -
return INPUT_PASS_TO_HANDLERS | INPUT_SLOT; -
} -
-
return INPUT_PASS_TO_HANDLERS; -
}
首先说明的是过滤处理,如果code不是ABS_MT_FIRST到ABS_MT_LAST之间,那就是单点上报(比如ABS_X);否则符合多点上报;它们的事件值value存储的位置是不一样的,所以取pold指针的方式是不一样的。(这个pold是过滤之后存的*pold = *pval;)。input_defuzz_abs_event()会对比当前value和上一次的old value;如果一样就过滤掉;不产生事件,但是只针对type B进行处理;type B的framework层sync后是不会清除slot的,所以要确保上报数据的准确;type A的sync后会清除slot。
if (code == ABS_MT_SLOT)只记录当前传输的slot,就是id;mt->slot = *pval;为什么这样做?这是对多点上报type B的处理,type B report首先report的就是type=EV_ABS,code=ABS_MT_SLOT,还有触点id为参数;一般type B接下来会依次report ABS_MT_TRACKING_ID、ABS_MT_TOOL_TYPE、ABS_MT_POSITION_X、ABS_MT_POSITION_Y等。所以此时记录下这个触点id,等下次report ABS_MT_TRACKING_ID时会处理这个code,如果只单一处理code=ABS_MT_SLOT,对用户来说没有意义。report ABS_MT_TRACKING_ID时会一直走到最后return INPUT_PASS_TO_HANDLERS | INPUT_SLOT;input_handle_event()里会根据INPUT_SLOT标志填充input_value v = &dev->vals[dev->num_vals++];将later的ABS_MT_SLOT补上。再下一个report ABS_MT_TOOL_TYPE时,是否会再走到这里来来补填一个ABS_MT_SLOT呢?看input_handle_abs_event()中最后的判断条件上次mt->slot != input_abs_get_val(dev, ABS_MT_SLOT)的时候,就input_abs_set_val(dev, ABS_MT_SLOT, mt->slot);,既然上一次已经set了新值,那此时条件就不成立了,所以只return INPUT_PASS_TO_HANDLERS,而不会再次填充一个code为ABS_MT_SLOT的input_value。
回到input_handle_event(),填充&dev->vals[dev->num_vals++]中的一个input_value结构。code为SYN_REPORT时返回INPUT_PASS_TO_HANDLERS | INPUT_FLUSH,所以会调用input_pass_values(dev, dev->vals, dev->num_vals)。如果指定了dev->grab指定了handle,就使用指定的;否则,遍历dev->h_list;找到dev上handle是open的,这个open什么时候设置?显然是应用层open的时候。dev->h_list的handle是在input device注册或者input handler注册的时候,匹配成功connect时,创建并初始化的,handle会把这两个结构联系到一起,继续执行input_to_handler()。
[cpp]
- static unsigned int input_to_handler(struct input_handle *handle,
- struct input_value *vals, unsigned int count)
- {
- struct input_handler *handler = handle->handler;
- struct input_value *end = vals;
- struct input_value *v;
- for (v = vals; v != vals + count; v++) {
- if (handler->filter &&
- handler->filter(handle, v->type, v->code, v->value))
- continue;
- if (end != v)
- *end = *v;
- end++;
- }
- count = end - vals;
- if (!count)
- return 0;
- if (handler->events)
- handler->events(handle, vals, count);
- else if (handler->event)
- for (v = vals; v != end; v++)
- handler->event(handle, v->type, v->code, v->value);
- return count;
- }
-
static unsigned int input_to_handler(struct input_handle *handle, -
struct input_value *vals, unsigned int count) -
{ -
struct input_handler *handler = handle->handler; -
struct input_value *end = vals; -
struct input_value *v; -
-
for (v = vals; v != vals + count; v++) { -
if (handler->filter && -
handler->filter(handle, v->type, v->code, v->value)) -
continue; -
if (end != v) -
*end = *v; -
end++; -
} -
-
count = end - vals; -
if (!count) -
return 0; -
-
if (handler->events) -
handler->events(handle, vals, count); -
else if (handler->event) -
for (v = vals; v != end; v++) -
handler->event(handle, v->type, v->code, v->value); -
-
return count; -
}
首先过滤,相同事件都合并,然后交给handler->events或者handler->event处理;前者是成批处理,后者是单一事件处理。
[cpp]
- static void evdev_events(struct input_handle *handle,
- const struct input_value *vals, unsigned int count)
- {
- struct evdev *evdev = handle->private;
- struct evdev_client *client;
- ktime_t time_mono, time_real;
- time_mono = ktime_get();
- time_real = ktime_sub(time_mono, ktime_get_monotonic_offset());
- rcu_read_lock();
- client = rcu_dereference(evdev->grab);
- if (client)
- evdev_pass_values(client, vals, count, time_mono, time_real);
- else
- list_for_each_entry_rcu(client, &evdev->client_list, node)
- evdev_pass_values(client, vals, count,
- time_mono, time_real);
- rcu_read_unlock();
- }
-
static void evdev_events(struct input_handle *handle, -
const struct input_value *vals, unsigned int count) -
{ -
struct evdev *evdev = handle->private; -
struct evdev_client *client; -
ktime_t time_mono, time_real; -
-
time_mono = ktime_get(); -
time_real = ktime_sub(time_mono, ktime_get_monotonic_offset()); -
-
rcu_read_lock(); -
-
client = rcu_dereference(evdev->grab); -
-
if (client) -
evdev_pass_values(client, vals, count, time_mono, time_real); -
else -
list_for_each_entry_rcu(client, &evdev->client_list, node) -
evdev_pass_values(client, vals, count, -
time_mono, time_real); -
-
rcu_read_unlock(); -
}
如果指定了client就用指定的,这个client是指evdev_client,否则遍历evdev->client_list,放到client_list的client中。client_list中的client是什么时候挂上的?(evdev_open()->evdev_attach_client()->list_add_tail_rcu(&client->node, &evdev->client_list))接下来evdev_pass_values会把事情交给client处理。
[cpp] view plain copy
- static void evdev_pass_values(struct evdev_client *client,
- const struct input_value *vals, unsigned int count,
- ktime_t mono, ktime_t real)
- {
- struct evdev *evdev = client->evdev;
- const struct input_value *v;
- struct input_event event;
- bool wakeup = false;
- event.time = ktime_to_timeval(client->clkid == CLOCK_MONOTONIC ?
- mono : real);
- /* Interrupts are disabled, just acquire the lock. */
- spin_lock(&client->buffer_lock);
- for (v = vals; v != vals + count; v++) {
- event.type = v->type;
- event.code = v->code;
- event.value = v->value;
- __pass_event(client, &event);
- if (v->type == EV_SYN && v->code == SYN_REPORT)
- wakeup = true;
- }
- spin_unlock(&client->buffer_lock);
- if (wakeup)
- wake_up_interruptible(&evdev->wait);
- }
-
static void evdev_pass_values(struct evdev_client *client, -
const struct input_value *vals, unsigned int count, -
ktime_t mono, ktime_t real) -
{ -
struct evdev *evdev = client->evdev; -
const struct input_value *v; -
struct input_event event; -
bool wakeup = false; -
-
event.time = ktime_to_timeval(client->clkid == CLOCK_MONOTONIC ? -
mono : real); -
-
/* Interrupts are disabled, just acquire the lock. */ -
spin_lock(&client->buffer_lock); -
-
for (v = vals; v != vals + count; v++) { -
event.type = v->type; -
event.code = v->code; -
event.value = v->value; -
__pass_event(client, &event); -
if (v->type == EV_SYN && v->code == SYN_REPORT) -
wakeup = true; -
} -
-
spin_unlock(&client->buffer_lock); -
-
if (wakeup) -
wake_up_interruptible(&evdev->wait); -
}
此时input_value需要转换为input_event;目的是为了添加时间信息。每个input_event都会__pass_event;收到SYNC后会设置wakeup标志,唤醒evdev->wait。这个wait也是connect时候初始化的,init_waitqueue_head(&evdev->wait);唤醒它干什么呢?因为用户如果读不到数据根据open标志O_NONBLOCK会发生阻塞;就是需要client中有数据时来唤醒。
[cpp]
- static void __pass_event(struct evdev_client *client,
- const struct input_event *event)
- {
- client->buffer[client->head++] = *event;
- client->head &= client->bufsize - 1;
- if (unlikely(client->head == client->tail)) {
- /*
- * This effectively "drops" all unconsumed events, leaving
- * EV_SYN/SYN_DROPPED plus the newest event in the queue.
- */
- client->tail = (client->head - 2) & (client->bufsize - 1);
- client->buffer[client->tail].time = event->time;
- client->buffer[client->tail].type = EV_SYN;
- client->buffer[client->tail].code = SYN_DROPPED;
- client->buffer[client->tail].value = 0;
- client->packet_head = client->tail;
- if (client->use_wake_lock)
- wake_unlock(&client->wake_lock);
- }
- if (event->type == EV_SYN && event->code == SYN_REPORT) {
- client->packet_head = client->head;
- if (client->use_wake_lock)
- wake_lock(&client->wake_lock);
- kill_fasync(&client->fasync, SIGIO, POLL_IN);
- }
- }
-
static void __pass_event(struct evdev_client *client, -
const struct input_event *event) -
{ -
client->buffer[client->head++] = *event; -
client->head &= client->bufsize - 1; -
-
if (unlikely(client->head == client->tail)) { -
/* -
* This effectively "drops" all unconsumed events, leaving -
* EV_SYN/SYN_DROPPED plus the newest event in the queue. -
*/ -
client->tail = (client->head - 2) & (client->bufsize - 1); -
-
client->buffer[client->tail].time = event->time; -
client->buffer[client->tail].type = EV_SYN; -
client->buffer[client->tail].code = SYN_DROPPED; -
client->buffer[client->tail].value = 0; -
-
client->packet_head = client->tail; -
if (client->use_wake_lock) -
wake_unlock(&client->wake_lock); -
} -
-
if (event->type == EV_SYN && event->code == SYN_REPORT) { -
client->packet_head = client->head; -
if (client->use_wake_lock) -
wake_lock(&client->wake_lock); -
kill_fasync(&client->fasync, SIGIO, POLL_IN); -
} -
}
client中一些字段的含义:
packet_head:一个数据包头;
head:动态索引,每加入一个event到buffer中,head++;
tail:也是动态索引,每取出一个buffer中的event,tail++;
buffer:event存储器,是一个环形区域。
__pass_event会把数据放到client->buffer中。
个人猜想:client->bufsize是一个2的次幂值,client->head &= client->bufsize - 1是为防止溢出,client->head == client->tail时,说明用户读的太快了,读的也是无效的。如果收到SYNC说明一个包结束了,更新一个包头packet_head,再上个锁wake_lock(&client->wake_lock);,这把锁在用户读取的时候会打开;向内核发送SIGIO,POLL_IN表示可读。
事件的传递过程:首先在驱动层调用inport_report_abs,然后调用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。
二 用户空间获取跟踪
[cpp]
- 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,
- .llseek = no_llseek,
- };
-
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, -
.llseek = no_llseek, -
};
evdev_connect()的时候,cdev_init(&evdev->cdev, &evdev_fops);初始化了eventx字符设备的操作函数集。
[cpp]
- static int evdev_open(struct inode *inode, struct file *file)
- {
- struct evdev *evdev = container_of(inode->i_cdev, struct evdev, cdev);
- unsigned int bufsize = evdev_compute_buffer_size(evdev->handle.dev);
- struct evdev_client *client;
- int error;
- client = kzalloc(sizeof(struct evdev_client) +
- bufsize * sizeof(struct input_event),
- GFP_KERNEL);
- if (!client)
- return -ENOMEM;
- client->bufsize = bufsize;
- spin_lock_init(&client->buffer_lock);
- snprintf(client->name, sizeof(client->name), "%s-%d",
- dev_name(&evdev->dev), task_tgid_vnr(current));
- client->evdev = evdev;
- evdev_attach_client(evdev, client);
- error = evdev_open_device(evdev);
- if (error)
- goto err_free_client;
- file->private_data = client;
- nonseekable_open(inode, file);
- return 0;
- err_free_client:
- evdev_detach_client(evdev, client);
- kfree(client);
- return error;
- }
-
static int evdev_open(struct inode *inode, struct file *file) -
{ -
struct evdev *evdev = container_of(inode->i_cdev, struct evdev, cdev); -
unsigned int bufsize = evdev_compute_buffer_size(evdev->handle.dev); -
struct evdev_client *client; -
int error; -
-
client = kzalloc(sizeof(struct evdev_client) + -
bufsize * sizeof(struct input_event), -
GFP_KERNEL); -
if (!client) -
return -ENOMEM; -
-
client->bufsize = bufsize; -
spin_lock_init(&client->buffer_lock); -
snprintf(client->name, sizeof(client->name), "%s-%d", -
dev_name(&evdev->dev), task_tgid_vnr(current)); -
client->evdev = evdev; -
evdev_attach_client(evdev, client); -
-
error = evdev_open_device(evdev); -
if (error) -
goto err_free_client; -
-
file->private_data = client; -
nonseekable_open(inode, file); -
-
return 0; -
-
err_free_client: -
evdev_detach_client(evdev, client); -
kfree(client); -
return error; -
}
evdev结构是怎么找到的?已知该结构中的cdev指针,找到这个结构;说明初始化evdev的时候,evdev->cdev就对应这个eventx;这也是connect做的事情。bufsize就是max(dev->hint_events_per_packet * EVDEV_BUF_PACKETS, EVDEV_MIN_BUFFER_SIZE);之后转化成2的次幂。终于看到client登场了。evdev_attach_client()->list_add_tail_rcu(&client->node, &evdev->client_list);把自己挂到了evdev->client_list上。这样,pass event的时候才能找到对应的client。
[cpp]
- static int evdev_open_device(struct evdev *evdev)
- {
- int retval;
- retval = mutex_lock_interruptible(&evdev->mutex);
- if (retval)
- return retval;
- if (!evdev->exist)
- retval = -ENODEV;
- else if (!evdev->open++) {
- retval = input_open_device(&evdev->handle);
- if (retval)
- evdev->open--;
- }
- mutex_unlock(&evdev->mutex);
- return retval;
- }
-
static int evdev_open_device(struct evdev *evdev) -
{ -
int retval; -
-
retval = mutex_lock_interruptible(&evdev->mutex); -
if (retval) -
return retval; -
-
if (!evdev->exist) -
retval = -ENODEV; -
else if (!evdev->open++) { -
retval = input_open_device(&evdev->handle); -
if (retval) -
evdev->open--; -
} -
-
mutex_unlock(&evdev->mutex); -
return retval; -
}
显然evdev->exist = true;也是connect时候做的事情。如果open成功会更新evdev->open计数。
[cpp]
- 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;
- }
-
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; -
}
回到了核心层,主要是更新handle->open和dev->users计数,成功open返回0,一层一层的返回0,返回到evdev_open()中file->private_data = client;猜测是为了read的时候找到这个client。
[cpp]
- 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;
- struct input_event event;
- size_t read = 0;
- int error;
- if (count != 0 && count < input_event_size())
- return -EINVAL;
- for (;;) {
- if (!evdev->exist)
- return -ENODEV;
- if (client->packet_head == client->tail &&
- (file->f_flags & O_NONBLOCK))
- return -EAGAIN;
- /*
- * count == 0 is special - no IO is done but we check
- * for error conditions (see above).
- */
- if (count == 0)
- break;
- while (read + input_event_size() <= count &&
- evdev_fetch_next_event(client, &event)) {
- if (input_event_to_user(buffer + read, &event))
- return -EFAULT;
- read += input_event_size();
- }
- if (read)
- break;
- if (!(file->f_flags & O_NONBLOCK)) {
- error = wait_event_interruptible(evdev->wait,
- client->packet_head != client->tail ||
- !evdev->exist);
- if (error)
- return error;
- }
- }
- return read;
- }
-
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; -
struct input_event event; -
size_t read = 0; -
int error; -
-
if (count != 0 && count < input_event_size()) -
return -EINVAL; -
-
for (;;) { -
if (!evdev->exist) -
return -ENODEV; -
-
if (client->packet_head == client->tail && -
(file->f_flags & O_NONBLOCK)) -
return -EAGAIN; -
-
/* -
* count == 0 is special - no IO is done but we check -
* for error conditions (see above). -
*/ -
if (count == 0) -
break; -
-
while (read + input_event_size() <= count && -
evdev_fetch_next_event(client, &event)) { -
-
if (input_event_to_user(buffer + read, &event)) -
return -EFAULT; -
-
read += input_event_size(); -
} -
-
if (read) -
break; -
-
if (!(file->f_flags & O_NONBLOCK)) { -
error = wait_event_interruptible(evdev->wait, -
client->packet_head != client->tail || -
!evdev->exist); -
if (error) -
return error; -
} -
} -
-
return read; -
}
果然第一件事就是找到evdev_client;就是evdev_open的时候记录的。*evdev = client->evdev也是evdev_open的时候记录的。input_event_size()是一个event的最小size,是input_event_compat或input_event结构的size,小于这个size的read操作无需理会。用了一个for循环,如果没有读到数据open的时候file->f_flags & O_NONBLOCK以非阻塞方式open会调用wait_event_interruptible()会阻塞到这里,等到client中有数据会唤醒它,前面已经说过了。如果evdev_open成功,evdev->exist会设置就继续走。一直走到了一个while循环,evdev_fetch_next_event()是从client中取出event。
[cpp]
- static int evdev_fetch_next_event(struct evdev_client *client,
- struct input_event *event)
- {
- int have_event;
- spin_lock_irq(&client->buffer_lock);
- have_event = client->packet_head != client->tail;
- if (have_event) {
- *event = client->buffer[client->tail++];
- client->tail &= client->bufsize - 1;
- if (client->use_wake_lock &&
- client->packet_head == client->tail)
- wake_unlock(&client->wake_lock);
- }
- spin_unlock_irq(&client->buffer_lock);
- return have_event;
- }
-
static int evdev_fetch_next_event(struct evdev_client *client, -
struct input_event *event) -
{ -
int have_event; -
-
spin_lock_irq(&client->buffer_lock); -
-
have_event = client->packet_head != client->tail; -
if (have_event) { -
*event = client->buffer[client->tail++]; -
client->tail &= client->bufsize - 1; -
if (client->use_wake_lock && -
client->packet_head == client->tail) -
wake_unlock(&client->wake_lock); -
} -
-
spin_unlock_irq(&client->buffer_lock); -
-
return have_event; -
}
如果packet_head和tail不等,说明循环buffer里有数据,直接取出来,别忘了更新动态索引client->tail++。如果首尾相接了,说明数据读完了。wake_unlock(&client->wake_lock);;因为_pass_event中添加_event的时候上了一把锁wake_lock(&client->wake_lock);。
接着evdev_read,已经取到event,就可以送到用户空间了。input_event_to_user()也是通过copy_to_user()实现的,这个函数很眼熟啊。一直read到读够了count个数据或者读完了一个包,client->packet_head == client->tail就表示这个包读完了。如果两个进程打开同一个文件,每个进程在open时都会生成一个evdev_client,evdev_client被挂在evdev的client_list上,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。