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To: Rik van Riel <riel@conectiva.com.br>
Cc: Andrew Morton <akpm@digeo.com>, David Howells <dhowells@redhat.com>,
       Trond Myklebust <trond.myklebust@fys.uio.no>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] do_generic_file_read / readahead adjustments 
In-Reply-To: Message from Rik van Riel <riel@conectiva.com.br> 
   of "Wed, 16 Oct 2002 14:36:14 -0200." <Pine.LNX.4.44L.0210161435470.1648-100000@duckman.distro.conectiva> 
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Date: Wed, 16 Oct 2002 18:55:45 +0100
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From: David Howells <dhowells@cambridge.redhat.com>
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> On Wed, 16 Oct 2002, Andrew Morton wrote:
> > David Howells wrote:
> > >
> > > The attached patch does the following three things:
> >
> > Seems sensible.  Is there something out there which actually uses this?
> 
> I think David has a few things up his sleeve.  The patch looks
> sensible.

I'm writing a general cache for filesystems such as AFS, NFSv4, and
Lustre. Block devices are made available to the "cache manager" by means of a
filesystem that can be mounted. I'm storing meta data in an inode in the
cache, but to scan this at the moment I need to gain a "struct file" to use
with do_generic_file_read().

This involves either creating a dummy dentry and struct file (which will cause
Al Viro to come looking for me with a shotgun), or to use an extra auxilliary
filesystem mounted with do_kern_mount(), neither of which are particularly
appealing.

This patch is the alternative: make a function (do_generic_mapping_read())
that I can pass an inode or an address_space to, and make
do_generic_file_read() call that. This allows me to make use of readahead
semantics without having to reinvent them for myself.

David
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