SCSI scanner device ownership and permissions

[D. Hugh Redelmeier]

| From: Paul Howarth <paul at city-fan.org>

| It tells me how to write a udev rule that will create an appropriate
| link for your scanner at boot time :-)

Ah.  udev(8) explains this.  I know you know, but I am stating this
for others who read this thread.

| Create a file /etc/udev/rules.d/10-custom.rules containing the following
| line:
| 
| BUS="scsi", SYSFS{vendor}="UMAX*", SYSFS{model}="Astra*", SYMLINK="scanner%n"

[This should be in one line.]

| You should get an appropriate symlink created next time the sg module is
| loaded (e.g. at reboot). The name of the symlink is such that the
| existing "console" rules will change ownership of the device to the
| currently-logged-in user.

This works well.  Thanks!

Is there a reason that this line should not be included as a standard
part of /etc/udev/rules.d/50-udev.rules (which is in turn a part of
the udev rpm)?

The scanner isn't recognized when I turn on the scanner sometime after
booting.  As far as I can make out from reading proc(5)'s
/proc/scsi/scsi entry, I need to prod the scsi system to rescan the
bus.  In my case, it did so when I (as root) issued:

	echo 'scsi add-single-device 0 0 5 0' >/proc/scsi/scsi
	                                   ^ LUN
	                                 ^ SCSI ID
	                               ^ host adapter channel
	                             ^ host adapter

Even though this seems to be a very specific request, it seemed to
cause all sorts of activity in the SCSI subsystem.  Here's the
relevant part of dmesg:

    usb 1-2.2: reset high speed USB device using ehci_hcd and address 6
    (scsi0:A:5:0): refuses WIDE negotiation.  Using 8bit transfers
    (scsi0:A:5:0): refuses synchronous negotiation. Using asynchronous transfers
      Vendor: UMAX      Model: Astra 1200S       Rev: V2.9
      Type:   Scanner                            ANSI SCSI revision: 02
     target0:0:5: Beginning Domain Validation
     target0:0:5: Ending Domain Validation
    Attached scsi generic sg0 at scsi1, channel 0, id 0, lun 0,  type 0
    Attached scsi generic sg1 at scsi1, channel 0, id 0, lun 1,  type 0
    Attached scsi generic sg2 at scsi1, channel 0, id 0, lun 2,  type 0
    Attached scsi generic sg3 at scsi1, channel 0, id 0, lun 3,  type 0
    Attached scsi generic sg4 at scsi0, channel 0, id 5, lun 0,  type 6

It seem especially funny that USB (scsi1) would get re-examined.  That is a
different host adapter.

Is there a way that the SCSI scanner could be automatically recognized
when it is turned on?