From owner-freebsd-arch@FreeBSD.ORG  Wed Jul 21 11:37:51 2004
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To: Doug Rabson <dfr@nlsystems.com>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Wed, 21 Jul 2004 12:20:54 BST."
             <1090408854.7114.8.camel@builder02.qubesoft.com> 
Date: Wed, 21 Jul 2004 13:37:50 +0200
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cc: arch@freebsd.org
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Subject: Re: kldunload DIAGNOSTIC idea... 
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In message <1090408854.7114.8.camel@builder02.qubesoft.com>, Doug Rabson writes
:

>> There are three parts to it, a refcount on cdevsw which tells us if
>> any thread is inside the driver using that route, a refcount on the
>> individual cdev and a linkage between the two.
>
>The device_busy() counter is still simplest (as long as there is a
>device_t at all). The implementation of devclass_delete_driver() will
>automatically veto the unload (when its called from
>driver_module_handler()).

The problem is that I cannot find the device_t without dereferencing
the struct cdev (either for si_driver[12] or the dev_t) and by then
it is too late.  There is no way we can avoid refcounting on the cdev.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.