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

Dag-Erling Smørgrav des at
Wed Feb 28 08:58:18 UTC 2007

Warner Losh <imp at> writes:
>   Log:
>   Some USB mass storage devices return the number of sectors in response
>   to a READ_CAPACITY request rather than the maximum sector (off by one
>   problem).  This causes a huge cascade of errors as the geom tasting
>   code tries to read the last sector (which isn't really there in the
>   face of this error).  automated tools that manipulate disk labels and
>   such also have issues.
>   Create a new quirk READ_CAPACITY_OFFBY1 and add a quirk for the
>   SanDISK ImageMate that I have that suffers from this problem (the
>   SDDR-31).  It intercepts the READ_CAPACITY response and adjusts it
>   from number of sectors to max sector for devices with this quirk.
>   Reading the Linux source suggests that there are a host of
>   other devices with this issue, including iPods and some popular
>   cameras.  I've not added quirks for them, since I don't have the
>   devices in front of me to test.

How about the following dirty hack: if the appropriate kernel option /
device hint / sysctl knob is frobbed, when a READ_CAPACITY request
completes, try to read the last sector, and if that doesn't work,
adjust the result and print a warning to the console?

Dag-Erling Smørgrav - des at

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