Date: Tue, 4 Apr 2000 06:12:50 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: "Justin T. Gibbs" <gibbs@FreeBSD.org>, cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/kern kern_mib.c vfs_bio.c src/sys/sys buf.h Message-ID: <Pine.BSF.4.21.0004040545020.977-100000@alphplex.bde.org> In-Reply-To: <14634.954691700@critter.freebsd.dk>
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On Sun, 2 Apr 2000, Poul-Henning Kamp wrote:
> In message <Pine.BSF.4.21.0004030144330.1715-100000@alphplex.bde.org>, Bruce Ev
> ans writes:
>
> >"struct bio" is unfortunately even more block-specific than "struct buf",
> >since it doesn't have anything like "off_t b_offset". b_offset is
> >currently used mainly in the acd driver to handle weird block sizes.
>
> Well, I have b_offset in my cross-hair, because I know sos will roast
> me if I don't handle that case also :-)
>
> As far as I know, b_offset is only really used for physio and the only
> two drivers who understand non DEV_BSIZE multiple requests are the
> scsi-tape and atapi-cd drivers.
The disk layer already handles special sector sizes without adding much
overhead to the usual case. I hope it can do something similar for
b_offset. E.g., only one of { b_blkno, b_offset } needs to be valid.
Theat one could be maintained by all layers and the other one ignored
by all layers.
> The question at the heart of this is really: do we want to suffer
> the overhead of converting from byte offsets to sector number all
> the time or do we want to optimize for the predominantly used
> concept of sectors ?
I don't want conversions just to match the interface.
Bruce
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