Linux的uevent事件機制

uevent事件機制

Linux設計了一種uevent的機制。當有新的設備加入的時候，將設備的信息發送消息到用戶態。而用戶態有一個udev的進程監聽這個信息。當收到信息后做一定的解析，根據解析到的結果和用戶程序的配置做一些處理，也包括加載驅動程序。

內核部分，Uevent是Kobject的一部分，用于在Kobject狀態發生改變時，例如增加、移除等，通知用戶空間程序,主要涉及kobject.h和kobject_uevent.c兩個文件，如下：

include/linux/kobject.h
lib/kobject_uevent.c

• 內核上報事件,調用kobject_uevent_env函數進行上報事件

• int kobject_uevent_env(struct kobjectkobj, enum kobject_action action,charenvp_ext[])

  static const char *kobject_actions[] ={
  [KOBJ_ADD] = “add”,
  [KOBJ_REMOVE] = “remove”,
  [KOBJ_CHANGE] = “change”,
  [KOBJ_MOVE] = “move”,
  [KOBJ_ONLINE] = “online”,
  [KOBJ_OFFLINE] = “offline”,
  };

比如下面的一個HDMI插拔的uevent字符串

 {SUBSYSTEM=extcon, SEQNUM=2706, ACTION=change, DEVTYPE=hdmi_audio, STATE=HDMI=1, DEVPATH=/devices/virtual/amhdmitx/amhdmitx0/hdmi_audio, NAME=hdmitx_extcon_audio}

android層面去讀取uevent事件

frameworks/base/core/jni/android_os_UEventObserver.cpp
uevent_init()  //open socket for UEventObserver
uevent_next_event(buffer, sizeof(buffer) //讀取uevent事件for (;;) {int length = uevent_next_event(buffer, sizeof(buffer) - 1);if (length <= 0) {return NULL;}buffer[length] = '\0';ALOGV("Received uevent message: %s", buffer);if (isMatch(buffer, length)) {// Assume the message is ASCII.jchar message[length];for (int i = 0; i < length; i++) {message[i] = buffer[i];}return env->NewString(message, length);}
}frameworks/base/core/java/android/os/UEventObserver.java
創建一個UEventThread線程不停的讀取消息while (true) {String message = nativeWaitForNextEvent();if (message != null) {if (DEBUG) {Log.d(TAG, message);}sendEvent(message);}}

amlogic平臺調試的例子

• 這里主要是添加了gpio按鍵的uevent事件上報給android,下面是一個上報的簡單例子，主要是傳輸字符串，這里可以任意指定

  char data[64];
  char *envp[] = { data, NULL };
  snprintf(data, sizeof(data), “code=%d,state=up”, key->code);
  kobject_uevent_env(&kp->config_dev->kobj, KOBJ_CHANGE, envp);

• app里面的修改

    mObserver.startObserving("DEVPATH=/devices/virtual/gpio_keyboard/gpio_keyboard");mObserver.startObserving("DEVPATH=/devices/adc_keypad.13/input/input1");private UEventObserver mObserver = new UEventObserver() {@Overridepublic void onUEvent(UEventObserver.UEvent event) {Log.i("onUEvent","event:"+event +"  code = "+event.get("code"));}};
  

• 注意點startObserving這個里面傳入的是設備的驅動路徑，必須填寫正確，onUEvent接收到的就是回調的時間信息

    09-11 00:08:59.942  7450  7474 I onUEvent: event:{DEVNAME=gpio_keyboard, SUBSYSTEM=gpio_keyboard, SEQNUM=4095, MAJOR=222, ACTION=change, DEVPATH=/devices/virtual/gpio_keyboard/gpio_keyboard, MINOR=0, code=473,state=down}  code = 473,state=down09-11 00:09:00.151  7450  7474 I onUEvent: event:{DEVNAME=gpio_keyboard, SUBSYSTEM=gpio_keyboard, SEQNUM=4096, MAJOR=222, ACTION=change, DEVPATH=/devices/virtual/gpio_keyboard/gpio_keyboard, MINOR=0, code=473,state=up}  code = 473,state=up09-11 00:08:55.147  7450  7474 I onUEvent: event:{PROP=0, SUBSYSTEM=input, PRODUCT=10/1/1/100, SEQNUM=4091, EV=100003, ACTION=change, DEVPATH=/devices/adc_keypad.13/input/input1, PHYS="adc_keypad/input0", KEY=3c000000 0 0 0 0 0 40000 0, NAME="adc_keypad", MODALIAS=input:b0010v0001p0001e0100-e0,1,14,k1DA,1DB,1DC,1DD,ramlsfw, code=477,state=down}  code = 477,state=down09-11 00:08:55.291  7450  7474 I onUEvent: event:{PROP=0, SUBSYSTEM=input, PRODUCT=10/1/1/100, SEQNUM=4092, EV=100003, ACTION=change, DEVPATH=/devices/adc_keypad.13/input/input1, PHYS="adc_keypad/input0", KEY=3c000000 0 0 0 0 0 40000 0, NAME="adc_keypad", MODALIAS=input:b0010v0001p0001e0100-e0,1,14,k1DA,1DB,1DC,1DD,ramlsfw, code=477,state=up}  code = 477,state=up
  

驅動舉例說明：

+++ b/drivers/gtinput/gtinput.c
@@ -344,11 +344,37 @@ static ssize_t gtinputdev_det_power_store(struct device *gtinput_class_dev,return size;}
+/* add by caizd for AC power detecte */
+static ssize_t gtinputdev_power_det_show(struct device *gtinput_class_dev,
+                               struct device_attribute *attr, char *buf)
+{
+       return sprintf(buf, "%s\n", "gtinput_power_det_show: sysfs test read");
+}
+
+static ssize_t gtinputdev_power_det_store(struct device *gtinput_class_dev,
+                               struct device_attribute *attr,
+                               const char *buf, size_t size)
+{
+       unsigned int usdata;
+       char kdata[64];
+       char *envp[] = {kdata, NULL};
+       int ret;
+
+       ret = sscanf(buf, "%d", &usdata);
+
+       snprintf(kdata, sizeof(kdata), "AC_power_det=%d", usdata);
+       kobject_uevent_env(&gtinput_class_dev->kobj, KOBJ_CHANGE, envp);
+//     printk("\n #####-czd-: AC_power_det=%d #####\n", usdata);
+
+       return size;
+}
+/* add end */static DEVICE_ATTR(gtinputdev_det_power, 0664, gtinputdev_det_power_show, gtinputdev_det_power_store);
+static DEVICE_ATTR(gtinputdev_power_det, 0664, gtinputdev_power_det_show, gtinputdev_power_det_store); /* add by caizd for AC power detecte */static const struct file_operations gtinput_fops = {.owner = THIS_MODULE,
@@ -403,6 +429,7 @@ static int gtinput_init(void)device_create_file(gtinput_class_dev, &dev_attr_gtinputdev_bat);device_create_file(gtinput_class_dev, &dev_attr_gtinputdev_bat_dc);device_create_file(gtinput_class_dev, &dev_attr_gtinputdev_det_power);
+       device_create_file(gtinput_class_dev, &dev_attr_gtinputdev_power_det); /* add by caizd for AC power detecte */