[patch] turning devctl into a "multiple openable" device

[Baptiste Daroussin]

On Wed, Nov 30, 2011 at 05:20:17PM +0100, Olivier Houchard wrote:
> On Wed, Nov 30, 2011 at 06:04:50PM +0200, Kostik Belousov wrote:
> > > > I wonder why the waiting_threads stuff is needed at all. The cv could
> > > > be woken up unconditionally everytime. What is the reason for the cv_wait
> > > > call in cdevpriv data destructor ? You cannot have a thread doing e.g.
> > > > read on the file descriptor while destructor is run.
> > > > 
> > > 
> > > What will prevent you from having a thread stuck in read(), while an another 
> > > one close() the fd ?
> > > 
> > Nothing, but file reference count goes to zero only after the thread
> > stuck in read is unstuck. Cdevpriv destructor is run only when file
> > reference count becomes zero, i.e. there can be no any accessing threads,
> > and new accesses are impossible since file descriptors also own references
> > on the file.
> 
> Right, I was a bit confused, this part can be removed.
> 
> Regards,
> 
> Olivier

Here is a new version of the patch mostly reworked by Olivier,
It doesn't duplicate anymore the devq, and fix all that have been
spotted here previously.

http://people.freebsd.org/~bapt/devctl_multi_open.diff

bonus, it removes the needless giant lock

regards,
Bapt
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