RE: [linux-usb-devel] Kernel unable to read partition table on US B Memory Key

["Roberts-Thomson, James" <James.Roberts-Thomson@NBNZ.CO.NZ>]

Alan,

Thanks very much for the input.

> > I'm trying to diagnose an issue with a USB "Memory Key" 
> (128Mb Flash 
> > drive) on my workstation (i386 Linux 2.6.12 kernel, using udev 058).
> > 
> > When connecting the key, the kernel fails to read the 
> partition table, 
> > and therefore the block device /dev/sda1 isn't created, so I can't 
> > mount the volume.  Calling "fdisk" manually, however, makes 
> it all work.
> 
> You don't even have to call fdisk.  Probably "touch /dev/sda" 
> would be enough.

Yes, indeed that does make it work.

> The device is not supposed to send the "Unit Attention, Not 
> ready to ready change" message more than once.  It's 
> violating the SCSI protocol by doing so.  (In fact it's not 
> supposed to send that message at all; it's supposed to send 
> "Power on or reset".)

Oh well, so much for the "Linux Compatible" markings on the box... :-)

> Replacing 
> the device won't help, because the device is behaving as 
> designed and the design is broken.

Yes, I'd imagine so, but I just wanted to make sure that it wasn't a bad
chip etc - generally speaking QA isn't what it used to be for most products
on the market these days.....

> What might help would be a direct comparison of the commands 
> being sent by Linux and by Windows.  If you turn on USB Mass 
> Storage verbose debugging
> (CONFIG_USB_STORAGE_DEBUG) in the kernel configuration then 
> the system debugging log will contain the commands sent by 
> usb-storage.  You can use a USB sniffer program like USB 
> Snoop (available from Sourceforge) to record the commands 
> sent by Windows.  Perhaps looking over the two logs will 
> reveal what magic command the device is waiting for.

OK, I'll try and do that today, and if I get anything meaningful, I'll send
it to the list(s).

One more additional note is that the key came with some s/w that allows you
to partition the key into "private" and "public" areas, where the private
area is accessed by a password.  Naturally, this s/w (Ustorage) is Windows
only; but looking at how it works under Windows it would appear that the key
has some firmware inside that is controlling access etc - could it be that
this firmware hasn't finished initialising by the time Linux tries to read
block 0, which is why the messages occur?

If this is the case, then a subtle delay somewhere in the initialisation
chain may help.  I'm not a Kernel Guru by any stretch, but I imagine the
sequence is something like this:

<key insert>
<usb subsystem identifies device>
<usb-storage driver takes device control> (existing specifiable delay in
here, via "delay_use")
<usb-storage drivers creates /dev/sdX> (via some form of udev interaction, I
guess...)
<sd_mod informed that new SCSI disk exists>
*
<sd_mod tries to read partition table etc>
<sd_mod creates /dev/sdXn entries> (also via udev)
...etc....

Perhaps the ability to create an additional "settle" delay at the "*" above
may help - presumably, I'd need to hack the sd_mod driver, so I'll have a
look there, too.

Thanks,

James Roberts-Thomson
----------
f u cn rd ths, u cn gt a gd jb n cmptr prgrmmng.

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