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DESIGN.md

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Sample configuration:

em /usr/bin/foo
em /usr/bin/bar
em /usr/local/bin/baz
em /opt/a/b

The following 7 directory watches (IN_CREATE|IN_MOVED_TO) are necessary:

  • / -> check for /usr/ or /opt/
  • /usr/ -> check for /usr/bin/ or /usr/local/
  • /usr/bin/ -> check for /usr/bin/foo or /usr/bin/bar
  • /usr/local/ -> check for /usr/local/bin/
  • /usr/local/bin/ -> check for /usr/local/bin/baz
  • /opt/ -> check for /opt/a/
  • /opt/a/ -> check for /opt/a/b

The configuration file is translated into 3 lookup tables tracking watch -> directory, directory -> { watch, children } and executable -> exception on start-up and then again whenever it is updated. At that point, all of the exceptions are applied.

Filesystem event are mapped to paths via the lookup table. Recursion through the directory tree will be triggered, removing the old watches from the table and adding new ones. Upon reaching a leaf node (executable), the exception will be applied.

The kernel will automatically close inotify watches when files are deleted. A call to inotify_rm_watch is actually incorrect because the descriptor may be released and recycled by another file at any point. This does mean that it will hold onto irrelevant watches if a directory is moved, but they will be released when it is removed.