getting from bio to buf in dastrategy()
Poul-Henning Kamp
phk at phk.freebsd.dk
Mon Aug 11 22:28:28 PDT 2003
In message <3F384C66.6060205 at 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 at 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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