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Date: Wed, 10 Mar 2004 23:38:28 -0800
From: Alfred Perlstein <alfred@freebsd.org>
To: Colin Percival <colin.percival@wadham.ox.ac.uk>
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cc: Poul-Henning Kamp <phk@phk.freebsd.dk>
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Subject: Re: cvs commit: src/sys/sys mdioctl.h src/sys/dev/md md.c
	src/sbin/mdconfig mdconfig.8 mdconfig.c
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* Colin Percival <colin.percival@wadham.ox.ac.uk> [040310 22:31] wrote:
> At 06:13 11/03/2004, Poul-Henning Kamp wrote:
> >That is a matter of taste more than anything else.  A vnode backed md(4)
> >device is technically a layering violation, so either the syncer or
> >the md(4) code itself (or both) needs to be aware of the special case.
> 
> <kernelnewbie>
>   Is it really necessary for vnode-backed memory disks to be
> accessed through the filesystem?  Why can't md(4) hijack the
> disk blocks which constitute the file (telling the filesystem
> not to touch them, of course) and translate I/O operations
> directly into I/O on the underlying device?
> </kernelnewbie>

That would be harder and make it only work on filesystems that
support VOP_BMAP, unless it fell back to VOP_WRITE when BMAP
returned ENOTSUP.

(VOP_BMAP returns the disk locations for a range of a vnode)

Give it a try. :)

-- 
- Alfred Perlstein
- Research Engineering Development Inc.
- email: bright@mu.org cell: 408-480-4684