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From: Alexey Dobriyan <adobriyan@gmail.com>
To: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 1/2] Introduce tty_unregister_ldisc()
Date: Wed, 1 Jun 2005 19:22:52 +0400
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Cc: Paul Fulghum <paulkf@microgate.com>, Andrew Morton <akpm@osdl.org>,
       linux-kernel@vger.kernel.org
References: <200505312356.00853.adobriyan@gmail.com> <1117578491.4627.14.camel@at2.pipehead.org> <20050601054251.GA12275@infradead.org>
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On Wednesday 01 June 2005 09:42, Christoph Hellwig wrote:
> On Tue, May 31, 2005 at 05:28:11PM -0500, Paul Fulghum wrote:
> > An unmodified ldisc driver (externally maintained) will continue to call
> > tty_register_ldisc with NULL, but the new behavior will be to set the
> > ldisc pointer to NULL but have LDISC_FLAG_DEFINED set.
> > 
> > If you feel it is absolutely necessary to add this new function
> > for cosmetic reasons, then leave the old behavior in place
> > and make tty_unregister_ldisc a wrapper to tty_register_ldisc
> > that uses a NULL pointer.
> 
> Nah, we don't want to allow staying out of tree folks out of sync.  Adding
> a BUG_ON for ldisk beeing NULL is much more reasoable.

Why add BUG_ON?

	tty_register_ldisc(N_FOO, NULL);
			...
	tty_ldiscs[disc] = *new_ldisc;	<= NULL