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Date: Wed, 27 Apr 2011 23:14:36 +0200
From: Bartosz Fabianowski <freebsd@chillt.de>
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Cc: Kostik Belousov <kostikbel@gmail.com>, freebsd-hackers@freebsd.org,
	Hans Petter Selasky <hselasky@c2i.net>
Subject: Re: Is there some implicit locking of device methods?
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> If you have some sort of state that needs to get created on first
> open and then removed on last close [...] I would still depend on the
> cdevpriv destructor and use a reference count between open() and the
> destructor to know when to cleanup shared state.

Yes, this is what I am doing. I am maintaining a list of all file 
descriptors open on the device. Once the length of that list reaches 
zero, I do global clean-up in the cdevpriv destructor.