table of contents
|CH(4)||Device Drivers Manual||CH(4)|
ch — SCSI
media-changer (juke box) driver
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
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,
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
It is only necessary to explicitly configure one
ch device; data structures are dynamically allocated
as media changes are found on the SCSI bus.
User mode programs communicate with the changer driver through a number of ioctls which are described below. Changer element addresses used in the communication between the kernel and the changer device are mapped to zero-based logical addresses. Element types are specified as follows:
- Medium transport element (picker).
- Storage element (slot).
- Import/export element (portal).
- Data transfer element (drive).
The following ioctl(2) calls apply to the
changer. They are defined in the header file
- (struct changer_move) Move a medium from one element
to another (MOVE
MEDIUM) using the current picker. The source and destination
elements are specified in a changer_move structure, which includes at
least the following 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 */
CM_INVERTin the cm_flags field is set, the medium changer is instructed to flip the medium while moving it.
- (struct changer_exchange) Move the medium located in
the source element to the first destination element, and move the medium
that had been in the first destination 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 elements 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 */
CM_INVERT2may be set to flip the first or second medium during the exchange operation, respectively.
- (struct changer_position) Position the current
picker in front of the specified element. The element is specified with a
changer_position structure, which includes at least the following
u_int cp_type; /* element type */ u_int cp_unit; /* logical unit of element */ u_int cp_flags; /* misc. flags */
CP_INVERTto invert the picker during the operation.
- (int) Return the logical address of the current picker.
- (int) Select the picker specified by the given logical address.
- (struct changer_params) Return the configuration
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 import/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
CHIGSTATUSioctl to query the jukebox status.
- Perform the
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 provided that it has a
label reader. The
chdriver's status is not affected by this call.
- (struct changer_element_status_request) Perform the
STATUS call on the media changer device. 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
chdriver which contains the following fields:
u_int cesr_element_type; u_int cesr_element_base; u_int cesr_element_count; u_int cesr_flags; struct changer_element_status *cesr_element_status;
This structure is read by the driver to determine 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_VOLTAGSto indicate that volume tag (bar code) information is to be read from the jukebox and returned.
The cesr_element_base and cesr_element_count fields must be valid with respect to the physical configuration of the changer. If they are not, the
CHIOGSTATUSioctl returns the
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; /* element address in media changer */ u_char ces_flags; /* see CESTATUS definitions below */ u_char ces_sensecode; /* additional sense code for element */ u_char ces_sensequal; /* additional sense code qualifier */ u_char ces_invert; /* invert bit */ u_char ces_svalid; /* source address (ces_source) valid */ u_short ces_source; /* source address of medium */ changer_voltag_t ces_pvoltag; /* primary volume tag */ changer_voltag_t ces_avoltag; /* alternate 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 diagnostic purposes only.
The following flags are defined for the ces_flags field:
- A medium is present.
- The medium has been deposited by the operator (and not by a picker).
- The element is in an exceptional state (e.g. invalid barcode label, barcode not yet scanned).
- The element is accessible by the picker.
- The element supports medium export.
- The element supports medium import.
Note that not all flags are valid for all element types.
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
supports are not thoroughly 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 operation and other things.
- device entries
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.
ch driver appeared in
ch driver was written by
Jason R. Thorpe
And Communications, http://www.and.com/. It was
added to the system by Stefan Grefen
who apparently had such a device. It was ported to CAM by
was updated to support volume tags by Hans Huebner
|May 14, 1998||Debian|