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To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Mon, 06 Oct 2003 17:46:51 EDT."
             <200310062146.h96Lkpx0093486@khavrinen.lcs.mit.edu> 
Date: Mon, 06 Oct 2003 23:55:17 +0200
Message-ID: <26369.1065477317@critter.freebsd.dk>
cc: arch@FreeBSD.org
Subject: Re: Alignment of disk-I/O from userland. 
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In message <200310062146.h96Lkpx0093486@khavrinen.lcs.mit.edu>, Garrett Wollman
 writes:

>I think that gives us plenary authority to require appropriate
>alignment of data buffers used to access disk devices directly.

Well, apart from us wedging or botching the request rather than
return a consistent error we're standards compliant then.

It has been mentioned on #thatchannel that busdma should take care
of this by copying the request as necessary.  Faced with the prospect
of a request several megabytes in size, I don't like the prospect
of malloc/bcopy too much.

All in all, I would advocate that we decide that disks in FreeBSD
are allowed to return ENXIO if they get insufficiently aligned
requests.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.