Re: [PATCH resend 1/4] scsi/sr: add no_read_disc_info scsi_device flag

[James Bottomley <James.Bottomley-l3A5Bk7waGM@public.gmane.org>]

On Fri, 2010-07-23 at 10:52 +0200, Hans de Goede wrote:
> Some USB devices emulate a usb-mass-storage attached (scsi) cdrom device,
> usually this fake cdrom contains the windows software for the device.
> While working on supporting Appotech ax3003 based photoframes, which do
> this I discovered that they will go of into lala land when ever they
> see a READ_DISC_INFO scsi command.
> 
> Thus this patch adds a scsi_device flag (which can then be set by the
> usb-storage driver through an unsual-devs entry), to indicate this, and
> makes the sr driver honor this flag.
> 
> I know this sucks, but as discussed on linux-scsi list there is no other
> way to make this device work properly.
> 
> Looking at usb traces made under windows, windows never sends a
> READ_DISC_INFO during normal interactions with a usb cdrom device. So as
> this cdrom emulation thingie becomes more common we might see more of
> this problem.

So, I suppose we can do this.  I dislike threading device bugs like this
up and down the stack.  The usb stor_control_thread already does some
command filtering; if it just rejected this command and READ
CAPACITY(16) on the flags, I think it would be far less code and the
SCSI subsystem would just do the right thing.

I'd actually like to hear from USB what they'd prefer to do.

James


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