cvs commit: src/sys/dev/usb umass.c

Poul-Henning Kamp phk at
Wed Feb 28 10:47:05 UTC 2007

In message <20070228.033055.-135505832.imp at>, "M. Warner Losh" writes

>Others have observed that the number of sectors on a disk should be
>even.  Therefore if maxsectors returned is even, it implies an odd
>number of sectors and should be adjusted.

Hmm, although generally true for present day disks, I don't think
it is universal enough that I would want to rely solely on it.

>number of sectors and should be adjusted.  That might be an even
>easier path to follow...  I'm never sure when one can schedule
>additional I/O inside of cam...

Neither am I.

Thinking about it, geom_disk might be a better place for it anyway.

That way we could postpone announcment of the disk to GEOM tasting
until we know it can actually answer a request.   Spin-up and other
long delays will not affect the system nearly as hard as they can

Early on I thought about a mandatory "read first & last sector"
check for all providers created in geom, but dropped it due to the
excessive shake, rattle and roll of big diskfarms and complex
layouts.  But it might be a good idea to add it in a reduced form
applied to all providers which come in at rank==1 (that way we
would not do it for partitions, slices, mirrors etc).

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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