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2b14290078
The last_sector_bug flag was added to work around a bug in certain usb cardreaders, where they would crash if a multiple sector read included the last sector. The original implementation avoids this by e.g. splitting an 8 sector read which includes the last sector into a 7 sector read, and a single sector read for the last sector. The flag is enabled for all USB devices. This revealed a second bug in other usb cardreaders, which crash when they get a multiple sector read which stops 1 sector short of the last sector. Affected hardware includes the Kingston "MobileLite" external USB cardreader and the internal USB cardreader on the Asus EeePC. Extend the last_sector_bug workaround to ensure that any access which touches the last 8 hardware sectors of the device is a single sector long. Requests are shrunk as necessary to meet this constraint. This gives us a safety margin against potential unknown or future bugs affecting multi-sector access to the end of the device. The two known bugs only affect the last 2 sectors. However, they suggest that these devices are prone to fencepost errors and that multi-sector access to the end of the device is not well tested. Popular OS's use multi-sector accesses, but they rarely read the last few sectors. Linux (with udev & vol_id) automatically reads sectors from the end of the device on insertion. It is assumed that single sector accesses are more thoroughly tested during development. Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk> Tested-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com> |
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