Date: Tue, 12 Aug 2003 07:28:20 +0200 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Eno Thereska <eno@andrew.cmu.edu> Cc: freebsd hackers <freebsd-hackers@FreeBSD.ORG> Subject: Re: getting from bio to buf in dastrategy() Message-ID: <28859.1060666100@critter.freebsd.dk> In-Reply-To: Your message of "Mon, 11 Aug 2003 22:09:42 EDT." <3F384C66.6060205@andrew.cmu.edu>
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In message <3F384C66.6060205@andrew.cmu.edu>, Eno Thereska writes: > >>in /sys/cam/scsi/scsi_da.c the dastrategy() > >>function takes as an argument "struct bio* bp" > >>Now I need to get to the "struct *buf" that bp > >>belongs to. > > >You can't do that, there may not be any struct buf. > >How can a bio exist on it's own, unrelated to any buf? >Would that be a special case or does that happen all the >time? A concrete example would help. struct buf represents a block in the cache/VM system. struct bio represents a disk I/O request. For historical reasons, a buf contains a bio, but that is by no means the only way to create a bio. Throughout geom bio's are created a destroyed which have no relation to any specific buf, for instance to read the key sectors in gbde. -- 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.
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