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

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Message-Id: <E1NfYmD-0003Aj-N9@pomaz-ex.szeredi.hu>
Date:	Thu, 11 Feb 2010 14:08:13 +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:
> Hello,
> 
> On 02/11/2010 09:46 PM, Miklos Szeredi wrote:
> > The problem with that is you simply can't determine in advance where
> > the region will grow.  Okay, you can leave space according to the size
> > of the file, but the size of the file can grow too.
> > 
> > *This* is the complexity that I want to get rid of.
> 
> Alright, then let's talk about that, not SHMLBA which doesn't really
> have much to do with this.  So, you're basically saying that you want
> multiple address spaces.  In that case, the only logical abstraction
> for that are files.  ie. We need to be passing file descriptors to the
> server and asking the server which descriptor it would want to use,
> which was the previous implementation, which you objected mentioning
> that this type of direct mmap would probably be useful only for device
> mmap implementations.

No, I don't want to pass file descriptors (early fuse did use that for
readdir and it was a mistake).

Global address space for server side maps are OK.  What I mind is that
in the *absence* of server side maps the filesystem still has to deal
with the global address space (with all its quirks).  This is totally
unnecessary.

Thanks,
Miklos
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