On Mon, 2 Aug 2010, Hans de Goede wrote: > Hi, > > On 07/28/2010 03:19 PM, James Bottomley wrote: > > 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. > > > > I was sort of hoping that Alan Stern would reply to this, but maybe he is > on vacation? No, I'm here. I've been waiting to hear from Matt Dharm. He's the usb-storage maintainer, so it's his call. > The reason I've done this patchset this way, is that I've added several > other usb mass storage specific quirks in the past and each time the USB > guys said that they don't want to do any (extra) command filtering and > asked me to split the patch in a scsi / sd flag adding patch and a > patch for the usb mass storage driver to use that flag. In general it's hard to know how command filtering at the usb-storage level will interact with the higher SCSI layers. In this case we have James's assurance that it will be okay. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
