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Date: Mon, 13 Jun 2005 19:14:35 +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,
	Apache Xie <apachexm@hotmail.com>
Subject: Re: contigmalloc() and mmap()
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On Mon, Jun 13, 2005 at 10:50:26AM -0700, Julian Elischer wrote:
> 
> Several times in the past we've seen people complainign that Linux 
> allows a device driver to know
> who called it and somehow it seems to store somewhere some information 
> about who
> openned the device.. thos somehow allows linux to store an arbitrary 
> structure
> for each openning process.  I thin from the sond of it that he wants to 
> do something
> similar. From the sond of it he wants to have a different buffer be used 
> depending on
> who is calling. This would partly work but would not work when processes 
> fork etc.
> 
> I think Linux must do some extra housekeeping in this case.

What Linux does is pretty simple.  The driver has access to the file
structure, and this structure has a field for driver private data.
It can store private data in open and free it again in the release
callback.