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From: Hans Petter Selasky <hselasky@c2i.net>
To: Ed Schouten <ed@80386.nl>
Date: Thu, 9 Aug 2012 07:37:21 +0200
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Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-current@freebsd.org
Subject: Re: ttydev_cdevsw has no d_purge
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On Wednesday 08 August 2012 22:46:28 Ed Schouten wrote:
> Hi Hans,
> 
> 2012/8/8 Hans Petter Selasky <hselasky@c2i.net>:
> > Are you sure that the new softc won't be used in any callbacks when
> > tty_rel_gone() is called, except for tsw_free() ?
> 
> Yes. Otherwise you would have already seen a kernel panic. See
> /sys/sys/ttydevsw.h; it has assertions on the locking.
> 
> > It is like a drain state, where a unit is collected for free, and then
> > committed to free state when the tsw_free() is called. In the [unlocked]
> > time in between the unit cannot be re-used.
> 
> How is this different from calling alloc/free directly? Why would it
> need to go through this `drain' state?

Because multiple TTYS can share the same ucom unit, and then stuff gets more 
complicated. I would then need refcounting and such to figure out when to 
actually free everything. This is simply not needed.

I'll make a patch soonish to extend tty.h with a #define tty_set_softc() if 
you don't mind.

--HPS