EVFILT_VNODE doesn't scale to large directory trees?

Robert Bonomi bonomi at mail.r-bonomi.com
Mon Oct 25 04:48:41 UTC 2010

> From owner-freebsd-questions at freebsd.org  Sun Oct 24 22:17:42 2010
> Date: Sun, 24 Oct 2010 18:05:34 -0700
> From: Kenton Varda <temporal at gmail.com>
> To: freebsd-questions at freebsd.org
> Subject: EVFILT_VNODE doesn't scale to large directory trees?
> Hi all,
> I am trying to write some code which monitors a possibly-large directory
> tree for changes.  Specifically, it's a build system, and I want it to
> automatically start rebuilding whenever I modify a source file.
> So far the approach I've taken is to use EVFILT_VNODE to watch every file
> and directory in the tree.  This seems to work OK so far, but it worries me
> that I have to open() every single file.  When I ran the same code on
> Darwin, it promptly hit the open file descriptor limit, and I'm worried that
> FreeBSD will do the same on larger code trees.
> Is there any better way to accomplish this?  Hate to say it, but Linux's
> inotify() seems more scalable here.  From what I can tell from the docs, it
> doesn't require opening the watched files and it will even watch all files
> in a directory with one call.

You're re-inventing the wheel. 

1) Set up a 'makefile' for the entire tree.

2) set up a daemon task that
     a) cd's to the root direcory of the build tree,
     b) executes a loop, consisting of
	 1) the 'make all' command,
	 2) a reasonably short 'sleep'

If 'efficiency' is a concern, then establish a procedure for checking-out/
checking-in files from the repository.  When a file is checked in, check
for (a) it being a new file, *OR* (b) having changes from the prior version.
If either condition is true, fire off 'make' to do the necessary re-build.

NOTE:  'cvs' has the above feature as a built-in option.  simply specify
'make' as a program to be run when you do a 'cvs commit' to store changes
back into the repository.

Did I say soemthing about re-inventing the wheel??   <grin>

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