[ILUG] usb autodetection

[Gavin McCullagh]

On Sun, 01 Feb 2004, Darragh Bailey wrote:

> Got a problem with the way devices are plugged into usb ports and assigned
> devices. As I've a couple of devices, printer, pen-drive & memory-card reader I'd
> like to have /etc/fstab entries for them so that if anyone else in my family
> needs to use the computer (I've persuaded them to use linux over windows) that
> they can access these devices without any problems.
> 
> At the moment the devices /dev/sd[a-c] are assigned based on what order the usb
> devices are plugged in and activeded. 

I may be wrong here but as I understand it one change in the 2.6 kernel
quite directly addresses this.  

http://www.infoworld.com/infoworld/article/04/01/30/05FElinux_1.html

"Using udev, the system is able to follow devices as they move around on
connected busses, with the device identifier remaining static. For
instance, the first-seen SCSI device will remain as device sda, using the
serial number of the device as an identifier regardless of the order in
which it’s found during a later boot."

However, unless you're feeling rather brave I'd wait until Fedora are
packaging 2.6.  They're not yet right?

> so is there any way that I can control which /dev/sd[a-c] entry is assigned to
> which device. 

You could write yourself a little script which does it for you.  They're
likely all formatted vfat.  If you can identify something on each device
which characterises it as opposed to the others your script can pick the
mount point on that basis.  One possibility is the serial number.  I have a
pen-drive inserted now.  Looking in /proc:

gavin at robin gavin> cat /proc/scsi/usb-storage-0/1 
   Host scsi1: usb-storage
       Vendor: TwinMOS-PDM 
      Product: USB 2.0 Mobile Disk    
Serial Number: B090614503861
     Protocol: Transparent SCSI
    Transport: Bulk
         GUID: 126f1325000b090614503861
     Attached: No

so, your script might read the above file and have mount points associated 
with known serial numbers (and guests).  When they insert the device,
either the system or the user runs your simple script and it mounts all
devices it finds according to the mapping.  If it finds a new disk, it
should allocate a new mount-point automatically.

I'm afraid I'm going to leave the script as an exercise rather than
embarrass myself ;)

Gavin