Re: Handling erroneous READ CAPACITY response in sd.c

[Luben Tuikov <luben_tuikov@adaptec.com>]

Alan Stern wrote:
> Everything we've tried for detecting too-high-by-one READ CAPACITY
> responses has failed on one device or another.  I can't think of any way
> to detect the error at runtime, short of actually trying to read the last
> sector.  And that is not a good tactic because it will quite likely leave
> the device is some non-resettable hung-up state.  Even the heuristic that
> USB devices will always have an even number of sectors turns out to be
> wrong for the Apple iPod.
> 
> There doesn't seem to be anything left but blacklisting.  This could be
> done at the SCSI level or the usb-storage level.  It turns out there's
> actually an advantage to putting the entries in the usb-storage list:  In
> many cases a vendor will use a USB interface chip from another company,
> changing the vendor name stored in the INQUIRY data but leaving the USB
> vendor ID alone (so it reflects the chip designer, not the drive seller).  
> This means that a single USB blacklist could cover a range of devices that
> would require multiple SCSI blacklist entries.  I've actually seen
> something like this happen in a different context (the Panasonic DMC-LCx
> cameras with internal interfaces by Matsushita have different Product
> strings in their INQUIRY data but the same Product ID in their USB
> descriptors).
> 
> On the other hand, the adjustment of the READ CAPACITY value should still 
> be moved to sd.c from usb-storage.  This can be implemented easily enough 
> by adding a bitflag to the scsi_device structure; the flag could be set 
> either by a SCSI blist entry or by usb-storage in its slave_configure 
> routine.  The flag would tell sd_read_capacity to decrement the number of 
> sectors it receives from the device.

This sounds good.  Just to clarify: if we blacklist in usb-storage, then
I think there's no need to also blacklist in SCSI Core as well.  Let sd
use the flag to decrement the Returned LBA (effectively assign Returned
LBA to capacity rather than increment it and then assign it.)

	Luben