185 lines
6.3 KiB
ReStructuredText
185 lines
6.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=========================
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SCSI media changer driver
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=========================
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This is a driver for SCSI Medium Changer devices, which are listed
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with "Type: Medium Changer" in /proc/scsi/scsi.
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This is for *real* Jukeboxes. It is *not* supported to work with
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common small CD-ROM changers, neither one-lun-per-slot SCSI changers
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nor IDE drives.
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Userland tools available from here:
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http://linux.bytesex.org/misc/changer.html
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General Information
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-------------------
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First some words about how changers work: A changer has 2 (possibly
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more) SCSI ID's. One for the changer device which controls the robot,
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and one for the device which actually reads and writes the data. The
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later may be anything, a MOD, a CD-ROM, a tape or whatever. For the
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changer device this is a "don't care", he *only* shuffles around the
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media, nothing else.
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The SCSI changer model is complex, compared to - for example - IDE-CD
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changers. But it allows to handle nearly all possible cases. It knows
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4 different types of changer elements:
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=============== ==================================================
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media transport this one shuffles around the media, i.e. the
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transport arm. Also known as "picker".
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storage a slot which can hold a media.
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import/export the same as above, but is accessible from outside,
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i.e. there the operator (you !) can use this to
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fill in and remove media from the changer.
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Sometimes named "mailslot".
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data transfer this is the device which reads/writes, i.e. the
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CD-ROM / Tape / whatever drive.
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=============== ==================================================
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None of these is limited to one: A huge Jukebox could have slots for
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123 CD-ROM's, 5 CD-ROM readers (and therefore 6 SCSI ID's: the changer
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and each CD-ROM) and 2 transport arms. No problem to handle.
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How it is implemented
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---------------------
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I implemented the driver as character device driver with a NetBSD-like
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ioctl interface. Just grabbed NetBSD's header file and one of the
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other linux SCSI device drivers as starting point. The interface
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should be source code compatible with NetBSD. So if there is any
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software (anybody knows ???) which supports a BSDish changer driver,
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it should work with this driver too.
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Over time a few more ioctls where added, volume tag support for example
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wasn't covered by the NetBSD ioctl API.
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Current State
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-------------
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Support for more than one transport arm is not implemented yet (and
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nobody asked for it so far...).
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I test and use the driver myself with a 35 slot cdrom jukebox from
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Grundig. I got some reports telling it works ok with tape autoloaders
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(Exabyte, HP and DEC). Some People use this driver with amanda. It
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works fine with small (11 slots) and a huge (4 MOs, 88 slots)
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magneto-optical Jukebox. Probably with lots of other changers too, most
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(but not all :-) people mail me only if it does *not* work...
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I don't have any device lists, neither black-list nor white-list. Thus
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it is quite useless to ask me whenever a specific device is supported or
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not. In theory every changer device which supports the SCSI-2 media
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changer command set should work out-of-the-box with this driver. If it
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doesn't, it is a bug. Either within the driver or within the firmware
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of the changer device.
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Using it
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--------
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This is a character device with major number is 86, so use
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"mknod /dev/sch0 c 86 0" to create the special file for the driver.
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If the module finds the changer, it prints some messages about the
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device [ try "dmesg" if you don't see anything ] and should show up in
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/proc/devices. If not.... some changers use ID ? / LUN 0 for the
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device and ID ? / LUN 1 for the robot mechanism. But Linux does *not*
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look for LUNs other than 0 as default, because there are too many
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broken devices. So you can try:
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1) echo "scsi add-single-device 0 0 ID 1" > /proc/scsi/scsi
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(replace ID with the SCSI-ID of the device)
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2) boot the kernel with "max_scsi_luns=1" on the command line
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(append="max_scsi_luns=1" in lilo.conf should do the trick)
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Trouble?
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--------
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If you insmod the driver with "insmod debug=1", it will be verbose and
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prints a lot of stuff to the syslog. Compiling the kernel with
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CONFIG_SCSI_CONSTANTS=y improves the quality of the error messages a lot
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because the kernel will translate the error codes into human-readable
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strings then.
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You can display these messages with the dmesg command (or check the
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logfiles). If you email me some question because of a problem with the
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driver, please include these messages.
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Insmod options
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--------------
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debug=0/1
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Enable debug messages (see above, default: 0).
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verbose=0/1
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Be verbose (default: 1).
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init=0/1
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Send INITIALIZE ELEMENT STATUS command to the changer
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at insmod time (default: 1).
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timeout_init=<seconds>
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timeout for the INITIALIZE ELEMENT STATUS command
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(default: 3600).
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timeout_move=<seconds>
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timeout for all other commands (default: 120).
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dt_id=<id1>,<id2>,... / dt_lun=<lun1>,<lun2>,...
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These two allow to specify the SCSI ID and LUN for the data
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transfer elements. You likely don't need this as the jukebox
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should provide this information. But some devices don't ...
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vendor_firsts=, vendor_counts=, vendor_labels=
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These insmod options can be used to tell the driver that there
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are some vendor-specific element types. Grundig for example
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does this. Some jukeboxes have a printer to label fresh burned
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CDs, which is addressed as element 0xc000 (type 5). To tell the
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driver about this vendor-specific element, use this::
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$ insmod ch \
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vendor_firsts=0xc000 \
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vendor_counts=1 \
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vendor_labels=printer
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All three insmod options accept up to four comma-separated
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values, this way you can configure the element types 5-8.
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You likely need the SCSI specs for the device in question to
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find the correct values as they are not covered by the SCSI-2
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standard.
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Credits
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-------
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I wrote this driver using the famous mailing-patches-around-the-world
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method. With (more or less) help from:
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- Daniel Moehwald <moehwald@hdg.de>
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- Dane Jasper <dane@sonic.net>
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- R. Scott Bailey <sbailey@dsddi.eds.com>
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- Jonathan Corbet <corbet@lwn.net>
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Special thanks go to
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- Martin Kuehne <martin.kuehne@bnbt.de>
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for a old, second-hand (but full functional) cdrom jukebox which I use
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to develop/test driver and tools now.
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Have fun,
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Gerd
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Gerd Knorr <kraxel@bytesex.org>
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