2

所以，我有一个应用程序，我想在 linux 上收到关于 hotplug 事件的通知。自然，我查看了 libudev 及其API。我还找到了有关如何将 select() 与 libudev 一起使用的有用教程。按照教程并浏览 API，我想出了这个示例程序，它等待热插拔事件，然后输出有关刚刚添加或删除的设备的一些基本信息。

#include <poll.h>
#include <libudev.h>
#include <stdexcept>
#include <iostream>

udev* hotplug;
udev_monitor* hotplug_monitor;

void init()
{
  // create the udev object
  hotplug = udev_new();
  if(!this->hotplug)
  {
    throw std::runtime_error("cannot create udev object");
  }

  // create the udev monitor
  hotplug_monitor = udev_monitor_new_from_netlink(hotplug, "udev");

  // start receiving hotplug events
  udev_monitor_enable_receiving(hotplug_monitor);
}

void deinit()
{
  // destroy the udev monitor
  udev_monitor_unref(hotplug_monitor);

  // destroy the udev object
  udev_unref(hotplug);
}

void run()
{
  // create the poll item
  pollfd items[1];
  items[0].fd = udev_monitor_get_fd(hotplug_monitor);
  items[0].events = POLLIN;
  items[0].revents = 0;

  // while there are hotplug events to process
  while(poll(items, 1, 50) > 0)
  {
    // XXX
    std::cout << "hotplug[ " << items[0].revents << " ]" << std::endl;

    // receive the relevant device
    udev_device* dev = udev_monitor_receive_device(hotplug_monitor);
    if(!dev)
    {
      // error receiving device, skip it
      continue;
    }

    // XXX
    std::cout << "hotplug[" << udev_device_get_action(dev) << "] ";
    std::cout << udev_device_get_devnode(dev) << ",";
    std::cout << udev_device_get_subsystem(dev) << ",";
    std::cout << udev_device_get_devtype(dev) << std::endl;

    // destroy the relevant device
    udev_device_unref(dev);

    // XXX
    std::cout << "done" << std::endl;

    // clear the revents
    items[0].revents = 0;
  }
}

int main(int args, char* argv[])
{
  init();

  while(true)
  {
    run();
  }

  deinit();
}

好吧，它不起作用。这是我插入 USB 鼠标时得到的输出。

hotplug[ 1 ]
hotplug[add] /dev/bus/usb/008/002,usb,usb_device
done
hotplug[ 1 ]
hotplug[add]

此时程序冻结，我必须用 Ctrl-C 停止它。我究竟做错了什么？

4

1 回答 1

4

The program doesn't actually stop; it continues running, but std::cout gets messed up when you try to print a NULL string (not all events have all properties). A fix is to make the three prints (devnode, subsystem, devtype) conditional.

于 2012-04-23T21:27:42.437 回答