Linux设备模型(四) - uevent应用：内核发送uevent，用户空间接收uevent

1，内核发送uevent

内���发送uevent的API由lib/kobject_event.c文件实现，include/linux/kobject.h是头文件。

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enum kobject_action {        KOBJ_ADD,        KOBJ_REMOVE,        KOBJ_CHANGE,        KOBJ_MOVE,        KOBJ_ONLINE,        KOBJ_OFFLINE,        KOBJ_MAX};/* kobject_uevent不能用在中断上下文 */int kobject_uevent(struct kobject *kobj, enum kobject_action action);int kobject_uevent_env(struct kobject *kobj, enum kobject_action action, char *envp[]);

在driver中可以调用kobject_uevent或者kobject_uevent_env来向用户空间发送uevent

kobject_uevent默认会发送”ACTION=xxx”，”DEVPATH=xxx”，”SUBSYSTEM=xxx”这三个uevent环境变量。

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kobject_uevent_env可以发送一些如”xxx=xxx”的自定义的uevent环境变量。

static ssize_t esd_info_store(struct device *dev,                    struct device_attribute *attr,                    const char *buf, size_t count){    if (!buf || count pdev->dev.kobj, KOBJ_CHANGE);    return count;}static int test_uevent(struct device *dev,                struct kobj_uevent_env *env){        int ret = 0;        ret = add_uevent_var(env,"COMMENT=%s", "test uevent message");        if(ret)            return ret;    return 0;}const struct device_type my_dev_type ={        .name ="william_ts",        .uevent= test_uevent,};static int xxx_probe(struct platform_device *pdev){    pdev->dev.type = &my_dev_type;}

2，用户空间解析uevent

#define UEVENT_MSG_LEN 2048static void uevent_event(uint32_t /*epevents*/, int event_fd){    char msg[UEVENT_MSG_LEN + 2];    int n;    char *cp;    n = uevent_kernel_multicast_recv(event_fd, msg, UEVENT_MSG_LEN);    if (n = UEVENT_MSG_LEN) /* overflow -- discard */        return;    msg[n] = '
3，测试结果
';    msg[n + 1] = '';    cp = msg;    ALOGE("william get the uevent size n = %d, msg = %s", n, msg);    while(*cp) {        ALOGE("william receive the msg = %s", cp);        /* advance to after the next  */        while(*cp++)            ;    }    ALOGE("william uevent received %s", msg);}void *MotTouch::uevent_thread_loop(void){    int epoll_fd, uevent_fd;    struct epoll_event ev;    int nevents = 0;    ALOGE("creating uevent thread");    uevent_fd = uevent_open_socket(64 * 1024, true);    if (uevent_fd = 0)        close(epoll_fd);    return NULL;}void sighandler(int sig) {  if (sig == SIGUSR1) {    destroyThread = true;    ALOGI("destroy set");    return;  }  signal(SIGUSR1, sighandler);}

上报的event会通知到所有的用户进程，这里能够收到系统中所有的uevent消息，这里只打印了我们自己添加测试的event

william get the uevent size n = 234, msg = change@/devices/platform/william_ts.0

william receive the msg = change@/devices/platform/william_ts.0

william receive the msg = ACTION=change

william receive the msg = DEVPATH=/devices/platform/william_ts.0

william receive the msg = SUBSYSTEM=platform

william receive the msg = DEVTYPE=william_ts

william receive the msg = DRIVER=william_ts

william receive the msg = MODALIAS=platform:william_ts

william receive the msg = MAC=05:04:03:02:01:00

william receive the msg = COMMENT=test uevent message

william receive the msg = SEQNUM=13492

william uevent received change@/devices/platform/william_ts.0