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Date: Mon, 13 Jun 2005 21:02:07 +0100
From: Christoph Hellwig <hch@infradead.org>
To: Julian Elischer <julian@elischer.org>
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Cc: Daniel Eischen <deischen@freebsd.org>, freebsd-hackers@freebsd.org,
	Scott Long <scottl@samsco.org>, Apache Xie <apachexm@hotmail.com>
Subject: Re: contigmalloc() and mmap()
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On Mon, Jun 13, 2005 at 08:59:17PM +0100, Christoph Hellwig wrote:
> disk drivers use a completely different set of entry points in Linux,
> and don't have access to per-fd data even in the case they're opened
> from userland.  Character drivers to which this applies OTOH always
> get a valid struct file, it's guranteed as part of the driver API.

That beeing said I'd suggest to not pass down the whole file struct
if you want to add this feature for freebsd but just some well-defined
API to store data in them.  Giving driver writers less rope to shoot
themselves improves averange driver quality significantly.  We'll probably
move towards such an API in Linux aswell one day, but it's a lot of work
once drivers have started to do all kinds of nasty things.