linux-kernel - Re: [PATCH] Export shmem_file_setup and shmem

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Date:	Sun, 10 Aug 2008 21:30:24 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Keith Packard <keithp@...thp.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Christoph Hellwig <hch@...radead.org>,
	Eric Anholt <eric@...olt.net>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Export shmem_file_setup and shmem_getpage for DRM-GEM

On Mon, Aug 04, 2008 at 06:09:24PM +0100, Hugh Dickins wrote:
> Whether such usage conforms to VFS API I'm not so sure: as I understand
> it, it's really for internal use by a filesystem - if it's going to be
> used beyond that, we ought to add a check that the filesystem it's used
> upon really has a ->readpage method (and I'd rather we add such a check
> than you do it at your end, in case we change the implementation later
> to use something other than a ->readpage method - Nick, you'll be
> nauseated to hear I was looking to see if ->fault with a pseudo-vma
> could do it).  But if the layering police are happy with this, I am.

Using read_mapping_page is fine on any pagecache backed file.  What is
much more difficult is actually writing into pagecache on a sub-page
level where we don't have proper APIs for anything but the filesystem
itself.

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