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Date: Tue, 17 Sep 2002 13:36:29 -0700
From: Andrew Morton <akpm@digeo.com>
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To: Alexander Viro <viro@math.psu.edu>
CC: Anton Altaparmakov <aia21@cantab.net>, ptb@it.uc3m.es,
       linux kernel <linux-kernel@vger.kernel.org>
Subject: Re: route inode->block_device in 2.5?
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Alexander Viro wrote:
> 
> ...
> There might be such thing as underlying block device of a <foofs> inode.

What he said.  Generally when the generic layers want to know
what the backing block_device is they defer this all the way down
to the point where they have called the filesystem's ->get_block
callback, and they pluck the block_dev pointer out of bh_result->b_bdev.

That's the only point at which it can be sanely resolved.

It may be different for different blocks of the file (striping;
swap_get_block() did this for the short period when it nearly
existed).
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