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

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Message-ID: <4B759635.1080908@kernel.org>
Date:	Sat, 13 Feb 2010 02:56:05 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Miklos Szeredi <miklos@...redi.hu>
CC:	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

Hello,

On 02/12/2010 10:53 PM, Miklos Szeredi wrote:
> That dev_offset value is used as an offset into the server side mmap
> address space.  And yes, vma->vm_pgoff and dev_offset should be SHMLBA
> multiples apart.

Alright.

> But don't call that _adjustment_.  That's totally confusing, these are
> *two* *different* *offsets*.

At this point, we're completely in the realm of the babel tower.
Unless we define all the terms explicitly, I don't think using or not
using a single word would make much difference.  Working with FUSE
gets a bit confusing regarding which term means what but with
multiple process address spaces and the dmmap address space and all
the offsets, it's getting pretty ridiculous.

> There's an alignment requirement but that's all.  If they are the
> same that is pure coincidence.
>
> And dev_offset (which points into the dmmap address space) is only
> required if the filesystem/CUSE driver needs server side mmap.

Hmmm... w/o the dev_offset how would the server designate which area
to use for the client?

Thanks.

-- 
tejun
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