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I've never used C before. this script adds a listener onto a directory and notifies the user by echoing to the terminal and then exiting whenever a file event happens. I want to modify the script to NOT exit but instead continuing monitoring the folder. I think the key might be this line:

length = read( fd, buffer, BUF_LEN );

but I don't really understand what is going on here. The description of the read() function is probably helpful for those who know C really well:

Using inotify is simple: Create a file descriptor, attach one or more watches (a watch is a path and set of events), and use the read() method to receive event information from the descriptor. Rather than burn scarce cycles, read() blocks until events occur.

but I don't fall into that category.

lollercoaster
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1 Answers1

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The program exists simply because nothing stops it from getting to exit( 0 ); once it has caught an event. You could wrap everything from fd = inotify_init(); to ( void ) close( fd ); in a loop and it will start over as long as you want it to.

The problem isn't in length = read( fd, buffer, BUF_LEN );. That part just waits for an event to happen and it doesn't call for the program to exit. It's really that the main is designed to be executed in one run-through and exit.

dee-see
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  • right. so what confused me about that was `while ( i < length )` is the loop condition where `length` is the variable mentioned in the `read()` call. why is a "length" used for the output of `read()`? – lollercoaster Jul 14 '11 at 18:30
  • `read()` reads directly into `buffer` and returns the number of bytes read, which is stored in `length`. I'm not entirely sure what the `while ( i < length )` condition is, but with each loop `i` is incremented by the length of an event so I assume the program can catch simultaneous events and the loop reads them all? I'm no C guru either so that's just my guess. – dee-see Jul 14 '11 at 19:16
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    That's correct. inotify can queue multiple events and then a `read()` will return them. The `while (i < length)` loop checks the result of one such `inotify` invocation. To do what the OP wants, he needs another (infinite) loop right before `length = read( fd, buffer, BUF_LEN );` and continuing till the end of the `while ( i < length )` loop (and a `break` for `length < 0` case). – Alok Singhal Jul 14 '11 at 20:42