USB: storage: add last-sector hacks
This patch (as1189b) adds some hacks to usb-storage for dealing with
the growing problems involving bad capacity values and last-sector
accesses:
A new flag, US_FL_CAPACITY_OK, is created to indicate that
the device is known to report its capacity correctly. An
unusual_devs entry for Linux's own File-backed Storage Gadget
is added with this flag set, since g_file_storage always
reports the correct capacity and since the capacity need
not be even (it is determined by the size of the backing
file).
An entry in unusual_devs.h which has only the CAPACITY_OK
flag set shouldn't prejudice libusual, since the device will
work perfectly well with either usb-storage or ub. So a
new macro, COMPLIANT_DEV, is added to let libusual know
about these entries.
When a last-sector access succeeds and the total number of
sectors is odd (the unexpected case, in which guessing that
the number is even might cause trouble), a WARN is triggered.
The kerneloops.org project will collect these warnings,
allowing us to add CAPACITY_OK flags for the devices in
question before implementing the default-to-even heuristic.
If users want to prevent the stack dump produced by the WARN,
they can disable the hack by adding an unusual_devs entry
for their device with the CAPACITY_OK flag.
When a last-sector access fails three times in a row and
neither the FIX_CAPACITY nor the CAPACITY_OK flag is set,
we assume the last-sector bug is present. We replace the
existing status and sense data with values that will cause
the SCSI core to fail the access immediately rather than
retry indefinitely. This should fix the difficulties
people have been having with Nokia phones.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
7 files changed