What are watch descriptors? (Linux subsystem inotify)

Question

I am currently using the inotify () system to monitor the activity of certain directories in the file system in my C code.

Now the procedure for using one of the following things is as follows. You take an integer (say event_notifier), turn it into an inotify descriptor using inotify_init (), for example

event_notifier=inotify_init();

Now suppose I want to keep track of events in several directories. Then I will add a clock to this event_notifier in these directories

wd1 = inotify_add_watch(event_notifier,"/../path..to..directory1/../",IN_ALL_EVENTS);
wd2 = inotify_add_watch(event_notifier,"/../path..to..directory2/../",IN_ALL_EVENTS);
wd3 = inotify_add_watch(event_notifier,"/../path..to..directory3/../",IN_ALL_EVENTS);
                            . . . . 
wdn = inotify_add_watch(event_notifier,"/../path..to..directoryn/../",IN_ALL_EVENTS);

Now I can add hours to several directories. Each of these calls returns a "clock descriptor" (wd1, wd2, wd3 .. wdn above). Whenever an event occurs in any of the directories, the inotify system sends the event to the inotify event_notifier descriptor description file along with the clock descriptor (wd1, wd2 ... wdn) corresponding to this particular "observable directory"

When an event arrives, I can read the event_notifier for the struct inotify_event array . This inotify_event structure has the following fields:

struct inotify_event  
{
  int wd; //Watch descriptor   
   ...  
  uint32_t len; //Size of 'name' field  
  char name[];  //null terminated name  
}

To read events, you simply do

read(event_notifier, buffer, sizeof(buffer))
struct inotify_event* event;
event=(struct inotify_event*)buffer; //Assuming only one event will occur

I am interested to know from which directory the notification came from. But when I stat () the clock descriptor it gives nothing

struct stat fileinfo;
fstat(event->wd, &fileinfo);
printf("\n Size of file is %l",fileinfo_st.size);

Even readlink () on / proc / self / fd / event-> fd did not return a single file name.

char filename[25]; 
readlink("/proc/self/fd/event-wd",filename,sizeof(filename));
printf("\n The filename is %s",filename);

I have two questions:

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2) , ?

Answer 1

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cat  /proc/sys/fs/inotify/max_user_watches

- , , :

sudo sysctl -w fs.inotify.max_user_watches=XXXXXX

---

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Answer 2

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wd1 = inotify_add_watch(
   event_notifier,
   "/../path..to..directory1/../",
   IN_ALL_EVENTS
   );