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CH(4)			 BSD Kernel Interfaces Manual			 CH(4)

     ch — SCSI media-changer (juke box) driver

     device ch

     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.

     It is only necessary to explicitly configure one ch device; data struc‐
     tures are dynamically allocated as media changes are found on the SCSI

     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:

     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 <sys/chio.h>.

     CHIOMOVE	   (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 */
		   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 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 spec‐
		   ified 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 exchange opera‐
		   tion, 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 includes at least
		   the following elements:

			 u_int cp_type;	 /* element type */
			 u_int cp_unit;	 /* logical unit of element */
			 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 current picker.

     CHIOSPICKER   (int) Select the picker specified by the given logical

     CHIOGPARAMS   (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

			 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 dimen‐
		   sions of the jukebox before using the CHIGSTATUS 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 provided that it
		   has a label reader.	The ch driver's status is not affected
		   by this call.

     CHIOGSTATUS   (struct changer_element_status_request) Perform the READ
		   ELEMENT 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

		   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

			 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_VOLTAGS to indicate that volume tag (bar code) infor‐
		   mation 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 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;	 /* 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

		   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 exceptional 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 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

     Many of the features the ch driver 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 flip‐
     ping, import/export element handling, multiple picker operation and other

     /dev/ch[0-9]  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.

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

     The ch driver appeared in 386BSD 0.1.

     The ch driver was written by Jason R. Thorpe ⟨⟩ for And
     Communications,  It was added to the system by
     Stefan Grefen ⟨⟩ who apparently had such a
     device.  It was ported to CAM by Kenneth Merry ⟨⟩.	It was
     updated to support volume tags by Hans Huebner ⟨⟩.

BSD				 May 14, 1998				   BSD

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