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-
-README for the SCSI media changer driver
-========================================
-
-This is a driver for SCSI Medium Changer devices, which are listed
-with "Type: Medium Changer" in /proc/scsi/scsi.
-
-This is for *real* Jukeboxes. It is *not* supported to work with
-common small CD-ROM changers, neither one-lun-per-slot SCSI changers
-nor IDE drives.
-
-Userland tools available from here:
- http://linux.bytesex.org/misc/changer.html
-
-
-General Information
--------------------
-
-First some words about how changers work: A changer has 2 (possibly
-more) SCSI ID's. One for the changer device which controls the robot,
-and one for the device which actually reads and writes the data. The
-later may be anything, a MOD, a CD-ROM, a tape or whatever. For the
-changer device this is a "don't care", he *only* shuffles around the
-media, nothing else.
-
-
-The SCSI changer model is complex, compared to - for example - IDE-CD
-changers. But it allows to handle nearly all possible cases. It knows
-4 different types of changer elements:
-
- media transport - this one shuffles around the media, i.e. the
- transport arm. Also known as "picker".
- storage - a slot which can hold a media.
- import/export - the same as above, but is accessible from outside,
- i.e. there the operator (you !) can use this to
- fill in and remove media from the changer.
- Sometimes named "mailslot".
- data transfer - this is the device which reads/writes, i.e. the
- CD-ROM / Tape / whatever drive.
-
-None of these is limited to one: A huge Jukebox could have slots for
-123 CD-ROM's, 5 CD-ROM readers (and therefore 6 SCSI ID's: the changer
-and each CD-ROM) and 2 transport arms. No problem to handle.
-
-
-How it is implemented
----------------------
-
-I implemented the driver as character device driver with a NetBSD-like
-ioctl interface. Just grabbed NetBSD's header file and one of the
-other linux SCSI device drivers as starting point. The interface
-should be source code compatible with NetBSD. So if there is any
-software (anybody knows ???) which supports a BSDish changer driver,
-it should work with this driver too.
-
-Over time a few more ioctls where added, volume tag support for example
-wasn't covered by the NetBSD ioctl API.
-
-
-Current State
--------------
-
-Support for more than one transport arm is not implemented yet (and
-nobody asked for it so far...).
-
-I test and use the driver myself with a 35 slot cdrom jukebox from
-Grundig. I got some reports telling it works ok with tape autoloaders
-(Exabyte, HP and DEC). Some People use this driver with amanda. It
-works fine with small (11 slots) and a huge (4 MOs, 88 slots)
-magneto-optical Jukebox. Probably with lots of other changers too, most
-(but not all :-) people mail me only if it does *not* work...
-
-I don't have any device lists, neither black-list nor white-list. Thus
-it is quite useless to ask me whenever a specific device is supported or
-not. In theory every changer device which supports the SCSI-2 media
-changer command set should work out-of-the-box with this driver. If it
-doesn't, it is a bug. Either within the driver or within the firmware
-of the changer device.
-
-
-Using it
---------
-
-This is a character device with major number is 86, so use
-"mknod /dev/sch0 c 86 0" to create the special file for the driver.
-
-If the module finds the changer, it prints some messages about the
-device [ try "dmesg" if you don't see anything ] and should show up in
-/proc/devices. If not.... some changers use ID ? / LUN 0 for the
-device and ID ? / LUN 1 for the robot mechanism. But Linux does *not*
-look for LUNs other than 0 as default, because there are too many
-broken devices. So you can try:
-
- 1) echo "scsi add-single-device 0 0 ID 1" > /proc/scsi/scsi
- (replace ID with the SCSI-ID of the device)
- 2) boot the kernel with "max_scsi_luns=1" on the command line
- (append="max_scsi_luns=1" in lilo.conf should do the trick)
-
-
-Trouble?
---------
-
-If you insmod the driver with "insmod debug=1", it will be verbose and
-prints a lot of stuff to the syslog. Compiling the kernel with
-CONFIG_SCSI_CONSTANTS=y improves the quality of the error messages a lot
-because the kernel will translate the error codes into human-readable
-strings then.
-
-You can display these messages with the dmesg command (or check the
-logfiles). If you email me some question because of a problem with the
-driver, please include these messages.
-
-
-Insmod options
---------------
-
-debug=0/1
- Enable debug messages (see above, default: 0).
-
-verbose=0/1
- Be verbose (default: 1).
-
-init=0/1
- Send INITIALIZE ELEMENT STATUS command to the changer
- at insmod time (default: 1).
-
-timeout_init=<seconds>
- timeout for the INITIALIZE ELEMENT STATUS command
- (default: 3600).
-
-timeout_move=<seconds>
- timeout for all other commands (default: 120).
-
-dt_id=<id1>,<id2>,...
-dt_lun=<lun1>,<lun2>,...
- These two allow to specify the SCSI ID and LUN for the data
- transfer elements. You likely don't need this as the jukebox
- should provide this information. But some devices don't ...
-
-vendor_firsts=
-vendor_counts=
-vendor_labels=
- These insmod options can be used to tell the driver that there
- are some vendor-specific element types. Grundig for example
- does this. Some jukeboxes have a printer to label fresh burned
- CDs, which is addressed as element 0xc000 (type 5). To tell the
- driver about this vendor-specific element, use this:
- $ insmod ch \
- vendor_firsts=0xc000 \
- vendor_counts=1 \
- vendor_labels=printer
- All three insmod options accept up to four comma-separated
- values, this way you can configure the element types 5-8.
- You likely need the SCSI specs for the device in question to
- find the correct values as they are not covered by the SCSI-2
- standard.
-
-
-Credits
--------
-
-I wrote this driver using the famous mailing-patches-around-the-world
-method. With (more or less) help from:
-
- Daniel Moehwald <moehwald@hdg.de>
- Dane Jasper <dane@sonic.net>
- R. Scott Bailey <sbailey@dsddi.eds.com>
- Jonathan Corbet <corbet@lwn.net>
-
-Special thanks go to
- Martin Kuehne <martin.kuehne@bnbt.de>
-for a old, second-hand (but full functional) cdrom jukebox which I use
-to develop/test driver and tools now.
-
-Have fun,
-
- Gerd
-
---
-Gerd Knorr <kraxel@bytesex.org>