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

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Date:	Thu, 11 Feb 2010 13:25:09 +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 Thu, 11 Feb 2010, Tejun Heo wrote:
> > And there's a weakness in the current server side mmap interface, for
> > example:
> > 
> >  1) user mmaps region 3-5 (in page index)
> >       server maps this region at 3-5
> > 
> >  2) user mmaps region 1-7
> >      server can't tell kernel that it wants to reuse region 3-5 but
> >      wants to create two other regions
> > 
> > What happens in that case?
> 
> If the server wants the two regions to be separate, it can map it to
> say 5-11 and returnt he offset of 5.  If it wants them to be shared,
> it will have to mmap 1-2 and 6-7 and return offset of 1.

What if region 6-7 is already occupied (e.g. because a separate region
was put there)?

Thanks,
Miklos
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