linux-kernel - Re: [fuse-devel] [PATCH] FUSE/CUSE: implement direct mmap support

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Message-Id: <E1NfE50-0001EK-Ao@pomaz-ex.szeredi.hu>
Date:	Wed, 10 Feb 2010 16:02:14 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Tejun Heo <tj@...nel.org>
CC:	miklos@...redi.hu, mszeredi@...e.cz, linux-kernel@...r.kernel.org,
	fuse-devel@...ts.sourceforge.net, polynomial-c@...too.org,
	akpm@...ux-foundation.org
Subject: Re: [fuse-devel] [PATCH] FUSE/CUSE: implement direct mmap support

On Wed, 10 Feb 2010, Tejun Heo wrote:
> > When does that happen?  Can it happen that two mappings of the same
> > file descriptor will have different backing pages?
> 
> Yeah, sure.  FUSE server is free to give them separate regions.  The
> only restriction is the SHMLBA alignment which is pretty easy to
> adhere to.

What I really meant was: does it ever happen that mapping a *single
open file* of a chardev twice will result in two different maps?
Or will the maps be only different if it was a different open of the
device?

If there's a pattern there, we might make the sharing/non-sharing
automated, and greatly simplify the interface.

Thanks,
Miklos
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