如何查看devices已经发送的uevent事件

在/sys/devices/ 下面的每一个device都有一个uevent attr，这个是rw的，通过cat uevent 可以知道这个device 已经向上层发送的event时间，向这个写的话，则可以向上层发送uenvent事件
linux-81uf:/sys/devices/pci0004:88 # ls -al
total 0
drwxr-xr-x  5 root root    0 Jun 19 02:33 .
drwxr-xr-x 18 root root    0 Jun 19 02:33 ..
drwxr-xr-x  4 root root    0 Jun 19 02:33 0004:88:00.0
lrwxrwxrwx  1 root root    0 Jun 20 04:47 firmware_node -> ../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:01
drwxr-xr-x  3 root root    0 Jun 19 02:33 pci_bus
drwxr-xr-x  2 root root    0 Jun 20 04:47 power
-rw-r--r--  1 root root 4096 Jun 19 02:33 uevent

linux-81uf:/sys/class/infiniband/hns_0 # ls
device  node_desc  node_type  power      sys_image_guid
fw_ver  node_guid  ports      subsystem  uevent
linux-81uf:/sys/class/infiniband/hns_0 # cat uevent
NAME=hns_0

与其对应的代码在drivers/base/core.c 中
对应的read函数
static ssize_t uevent_show(struct device *dev, struct device_attribute *attr,
               char *buf)
{
    struct kobject *top_kobj;
    struct kset *kset;
    struct kobj_uevent_env *env = NULL;
    int i;
    size_t count = 0;
    int retval;

    /* search the kset, the device belongs to */
    top_kobj = &dev->kobj;
    while (!top_kobj->kset && top_kobj->parent)
        top_kobj = top_kobj->parent;
    if (!top_kobj->kset)
        goto out;

    kset = top_kobj->kset;
    if (!kset->uevent_ops || !kset->uevent_ops->uevent)
        goto out;

    /* respect filter */
    if (kset->uevent_ops && kset->uevent_ops->filter)
        if (!kset->uevent_ops->filter(kset, &dev->kobj))
            goto out;

    env = kzalloc(sizeof(struct kobj_uevent_env), GFP_KERNEL);
    if (!env)
        return -ENOMEM;

    /* let the kset specific function add its keys */
    retval = kset->uevent_ops->uevent(kset, &dev->kobj, env);
    if (retval)
        goto out;

    /* copy keys to file */
    for (i = 0; i < env->envp_idx; i++)
        count += sprintf(&buf[count], "%s\n", env->envp[i]);
out:
    kfree(env);
    return count;
}
对应的写函数
static ssize_t uevent_store(struct device *dev, struct device_attribute *attr,
                const char *buf, size_t count)
{
    enum kobject_action action;

    if (kobject_action_type(buf, count, &action) == 0)
        kobject_uevent(&dev->kobj, action);
    else
        dev_err(dev, "uevent: unknown action-string\n");
    return count;
}
static DEVICE_ATTR_RW(uevent);

对应的event事件如下
static const char *kobject_actions[] = {
    [KOBJ_ADD] =        "add",
    [KOBJ_REMOVE] =        "remove",
    [KOBJ_CHANGE] =        "change",
    [KOBJ_MOVE] =        "move",
    [KOBJ_ONLINE] =        "online",
    [KOBJ_OFFLINE] =    "offline",
};