ch(4)

NAME

ch - SCSI media-changer (juke box) driver

SYNOPSIS

device ch
device ch1 target 4 unit 0

DESCRIPTION

The ch driver provides support for a SCSI media changer. It

allows many
slots of media to be multiplexed between a number of drives.

The changer
device may optionally be equipped with a bar code reader,

which reads
label information attached to the media.

A SCSI adapter must also be separately configured into the

system before
a SCSI changer can be configured.

As the SCSI adapter is probed during boot, the SCSI bus is

scanned for
devices. Any devices found which answer as 'Changer' type

devices will
be 'attached' to the ch driver. In FreeBSD releases prior

to 2.1, the
first found will be attached as ch0 and the next, ch1 etc.

Beginning in
2.1 it is possible to specify what ch unit a device should

come on line
as; refer to scsi(4) for details on kernel configuration.

KERNEL CONFIGURATION

In configuring, if an optional count is given in the speci

fication, that
number of SCSI media changers are configured; Most storage

for them is
allocated only when found so a large number of configured

devices is
cheap. (once the first has included the driver).

IOCTLS

User mode programs communicate with the changer driver

through a number
of ioctls which are described below. Changer element ad

dresses used in
the communication between the kernel and the changer device

are mapped to
zero-based logical addresses. Element types are specified

as follows:

CHET_MT Medium transport element (picker).

CHET_ST Storage element (slot).

CHET_IE Import/export element (portal).

CHET_DT Data transfer element (drive).

The following ioctl(2) calls apply to the changer. They are

defined in
the header file

CHIOMOVE (struct changer_move) Move a medium from one

element to

another (MOVE MEDIUM) using the current pick

er. The source
and destination elements are specified in a

changer_move
structure, which includes at least the follow

ing fields:

u_int cm_fromtype; /* element type to

move from */
u_int cm_fromunit; /* logical unit of

from element */
u_int cm_totype; /* element type to

move to */
u_int cm_tounit; /* logical unit of to

element */
u_int cm_flags; /* misc. flags */

If the CM_INVERT in the cm_flags field is set,

the medium
changer is instructed to flip the medium while

moving it.

CHIOEXCHANGE (struct changer_exchange) Move the medium lo

cated in the

source element to the first destination ele

ment, and move
the medium that had been in the first destina

tion element
to the second destination element. In case of

a simple
exchange, the source and second destination

elements should
be the same. The current picker is used to

perform the
operation. The addresses of the affected ele

ments is specified to the ioctl in a changer_exchange

structure which
includes at least the following fields:

u_int ce_srctype; /* element type

of source */
u_int ce_srcunit; /* logical unit

of source */
u_int ce_fdsttype; /* element type of

first destination */
u_int ce_fdstunit; /* logical unit of

first destination */
u_int ce_sdsttype; /* element type of

second destination */
u_int ce_sdstunit; /* logical unit of

second destination */
u_int ce_flags; /* misc. flags */

In ce_flags, CM_INVERT1 and/or CM_INVERT2 may

be set to
flip the first or second medium during the ex

change operation, respectively.

This operation is untested.

CHIOPOSITION (struct changer_position) Position the current

picker in

front of the specified element. The element

is specified
with a changer_position structure, which in

cludes at least
the following elements:

u_int cp_type; /* element type */
u_int cp_unit; /* logical unit of ele

ment */
u_int cp_flags; /* misc. flags */

The cp_flags field may be set to CP_INVERT to

invert the
picker during the operation.

CHIOGPICKER (int) Return the logical address of the cur

rent picker.

CHIOSPICKER (int) Select the picker specified by the given

logical

address.

CHIOGPARAMS (struct changer_params) Return the configura

tion parameters

for the media changer. This ioctl fills the

changer_params
structure passed by the user with at least the

following
fields:

u_int cp_npickers; /* number of pickers

*/
u_int cp_nslots; /* number of slots */
u_int cp_nportals; /* number of im

port/export portals */
u_int cp_ndrives; /* number of drives

*/

This call can be used by applications to query

the dimensions of the jukebox before using the CHIGSTA

TUS ioctl to
query the jukebox' status.

CHIOIELEM Perform the INITIALIZE ELEMENT STATUS call on

the media

changer device. This forces the media changer

to update
its internal status information with respect

to loaded
media. It also scans any barcode labels pro

vided that it
has a label reader. The ch driver's status is

not affected
by this call.

CHIOGSTATUS (struct changer_element_status_request) Per

form the READ

ELEMENT STATUS call on the media changer de

vice. This call
reads the element status information of the

media changer
and converts it to an array of

changer_element_status
structures.

With each call to CHIOGSTATUS, the status of

one or more
elements of one type may be queried.

The application passes a

changer_element_status_request structure to the ch driver which contains the

following
fields:

u_int cesr_ele

ment_type;
u_int cesr_ele

ment_base;
u_int cesr_ele

ment_count;
u_int cesr_flags;
struct changer_element_status *cesr_ele

ment_status;

This structure is read by the driver to deter

mine the type,
logical base address and number of elements

for which
information is to be returned in the array of
changer_element_status structures pointed to

by the
cesr_element_status field. The application

must allocate
enough memory for cesr_element_count status

structures (see
below). The cesr_flags can optionally be set

to
CESR_VOLTAGS to indicate that volume tag (bar

code) information is to be read from the jukebox and re

turned.

The cesr_element_base and cesr_element_count

fields must be
valid with respect to the physical configura

tion of the
changer. If they are not, the CHIOGSTATUS

ioctl returns
the EINVAL error code.

The information about the elements is returned

in an array
of changer_element_status structures. This

structure
include at least the following fields:

u_int ces_addr; /* ele

ment address in media changer */
u_char ces_flags; /* see

CESTATUS definitions below */
u_char ces_sensecode; /* addi

tional sense code for element */
u_char ces_sensequal; /* addi

tional sense code qualifier */
u_char ces_invert; /* in

vert bit */
u_char ces_svalid; /*

source address (ces_source) valid */
u_short ces_source; /*

source address of medium */
changer_voltag_t ces_pvoltag; /* pri

mary volume tag */
changer_voltag_t ces_avoltag; /* al

ternate volume tag */
u_char ces_idvalid; /*

ces_scsi_id is valid */
u_char ces_scsi_id; /* SCSI

id of element (if ces_idvalid is nonzero) */
u_char ces_lunvalid; /*

ces_scsi_lun is valid */
u_char ces_scsi_lun; /* SCSI

lun of element (if ces_lunvalid is nonzero) */

The ces_addr field contains the address of the

element in
the coordinate system of the media changer.

It is not used
by the driver, and should be used for diagnos

tic purposes
only.

The following flags are defined for the

ces_flags field:

CESTATUS_FULL A medium is present.

CESTATUS_IMPEXP The medium has been deposited

by the oper

ator (and not by a picker).

CESTATUS_EXCEPT The element is in an excep

tional state

(e.g. invalid barcode label,

barcode not
yet scanned).

CESTATUS_ACCESS The element is accessible by

the picker.

CESTATUS_EXENAB The element supports medium

export.

CESTATUS_INENAB The element supports medium

import.

Note that not all flags are valid for all ele

ment types.

NOTES

This version of the ch driver has been tested with a DEC

TZ875 (5 slot,
one DLT drive) and a Breece Hill Q47 (60 slot, four DLT

drives, barcode
reader).

Many of the features the ch driver supports are not thor

oughly tested due
to the fact that the devices available for testing do not

support the
necessary commands. This is true for alternate volume tags,

media flipping, import/export element handling, multiple picker opera

tion and other
things.

FILES

/dev/ch[0-9] device entries

DIAGNOSTICS

If the media changer does not support features requested by

the ch
driver, it will produce both console error messages and

failure return
codes to the ioctls described here.

SEE ALSO

chio(1), cd(4), da(4), sa(4)

HISTORY

The ch driver appeared in 386BSD 0.1.

AUTHORS

The ch driver was written by Jason R. Thorpe <thor

pej@and.com> for And
Communications, http://www.and.com/. It was added to the

system by
Stefan Grefen <grefen@goofy.zdv.uni-mainz.de> who apparently

had such a
device. It was ported to CAM by Kenneth Merry <ken@FreeB

SD.org>. It was
updated to support volume tags by Hans Huebner <hans@art

com.de>.

BSD May 14, 1998

BSD