问inotify_add_watch的fd参数是什么？

EN

first,  use inotify_init() or inotify_init1() to initialize an inotify 
instance;
second, return a file descriptor (with a new inotify event queue) fd ;
third, use the returned fd in inotify_add_watch to monitor the file path 
you want to monitor.

  int fd = inotify_init();                
  int wd = inotify_add_watch(fd, argv[1], IN_ALL_EVENTS);                  
  
  for (;;) 

  {   
       fd_set fds;   
       FD_ZERO(&fds);                
       FD_SET(fd, &fds);   


       if (select(fd + 1, &fds, NULL, NULL, NULL) > 0)       

       {   
           int len, index = 0;   
           while (((len = read(fd, &buf, sizeof(buf))) < 0) && (errno == EINTR));      
           while (index < len) 

           {   
                  event = (struct inotify_event *)(buf + index);                      
                  _inotify_event_handler(event);                                             
                  index += sizeof(struct inotify_event) + event->len;             
           }   
       }   
  }   
  
  inotify_rm_watch(fd, wd);             
  
  return 0;