uevent应用：内核发送uevent，用户空间接收uevent

1，内核发送uevent

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

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。

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 <= 0)return -EINVAL;kobject_uevent(&core_data->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 <= 0)return;if (n >= UEVENT_MSG_LEN) /* overflow -- discard */return;msg[n] = '\0';msg[n + 1] = '\0';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 \0 */while(*cp++);}ALOGE("william uevent received %s", msg);
}void *MT::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) {ALOGE("uevent_init: uevent_open_socket failed\n");return NULL;}fcntl(uevent_fd, F_SETFL, O_NONBLOCK);ev.events = EPOLLIN;ev.data.ptr = (void *)uevent_event;epoll_fd = epoll_create(64);if (epoll_fd == -1) {ALOGE("epoll_create failed; errno=%d", errno);goto error;}if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, uevent_fd, &ev) == -1) {ALOGE("epoll_ctl failed; errno=%d", errno);goto error;}while (!destroyThread) {struct epoll_event events[64];nevents = epoll_wait(epoll_fd, events, 64, -1);if (nevents == -1) {if (errno == EINTR) continue;ALOGE("usb epoll_wait failed; errno=%d", errno);break;}for (int n = 0; n < nevents; ++n) {if (events[n].data.ptr)(*(void (*)(uint32_t, int event_fd))events[n].data.ptr)(events[n].events, uevent_fd);}}ALOGI("exiting worker thread");
error:close(uevent_fd);if (epoll_fd >= 0)close(epoll_fd);return NULL;
}void sighandler(int sig) {if (sig == SIGUSR1) {destroyThread = true;ALOGI("destroy set");return;}signal(SIGUSR1, sighandler);
}

3，测试结果

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