Subject: Re: Are there drivers for Jaz USB drives? (YES!!)
From: Charles Lepple (firstname.lastname@example.org)
Date: Mon Apr 30 2001 - 15:57:38 MDT
--On Monday, April 30, 2001 4:49 PM +0200 "William K. Gibson"
> on 4/30/01 10:24 PM, Paul J. Lucas at email@example.com wrote:
>> Find out what the proper device major/minor numbers are; then,
>> in /etc/modules.conf, you can add a line of the form:
> Excuse my ignorance, but I have no idea what device major/minor numbers
> are. Would it be the same vendor/prod numbers given to me by the error
> message I reported earlier?
Here's a whirlwind tour of Unix devices. Skip to the last paragraph if you
just want to get the drive working at bootup :-)
There are two major types, block and character devices. Block devices are
typically hard drives, and character devices correspond to terminals
(console and pseudo-terminals -- /dev/tty[1-6] if you log in on the
console, /dev/pts/* if you telnet/ssh in), regular serial ports (*not
necessarily* USB devices), etc.
Major and minor numbers are the way the kernel identifies the devices
internally. You could rename your devices to be something like
/dev/scsi/id0 if you really wanted, but the kernel only cares about the
major/minor numbers. It's similar to the way that the kernel uses pathnames
to point to inodes (which is why you can open a file in one program, and
delete it while it is still open), but that's another story.
Given a device name (typically /dev/* but /dev is merely a convention) it
is easy to identify the type and major/minor numbers.
% ls -l /dev/sda /dev/sda1 /dev/sda2
brw-rw---- 1 root disk 8, 0 Aug 24 2000 /dev/sda
brw-rw---- 1 root disk 8, 1 Aug 24 2000 /dev/sda1
brw-rw---- 1 root disk 8, 2 Aug 24 2000 /dev/sda2
The 'b' in 'brw-rw----' indicates a block device ('c' for character
The '8' is the major number. This is the code for the first 15 SCSI devices
recognized by the kernel (cf /usr/src/linux/Documentation/devices.txt).
The next column over is the device minor number. As you may recognize from
the names, minor 0 is the whole disk, and subsequent numbers are partitions.
Now comes the fun part.
I don't have any external USB drives (let alone a Jaz) so this should be
taken with a grain of salt. But you mentioned that your drive worked when
you used /dev/sda2, so I would guess (YMMV; check 'ls -l /dev/sda2' to
confirm) that it is a block device, major 8, minor 2.
This would suggest using 'block-major-8-2 usb_storage' in the
/etc/modules.conf file. Having not tried this, though, I'd also suggest a
fallback of 'block-major-8 usb_storage' in case the module code doesn't
request driver modules based on the minor number. The caveat here is that
other SCSI devices may want different drivers. I'd give the first one a
-- Charles Lepple <firstname.lastname@example.org> http://ghz.cc/charles/
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