scsi(7)                                                             scsi(7)


   NAME
         scsi - common SCSI interface

   DESCRIPTION
         scsi refers to a common interface used by various hardware device
         drivers.  Specific details of each driver are presented elsewhere in
         this section; features common to them all are described here.

         The drivers that use scsi facilities are:

         hd    Hard Disk interface

         tp    Streaming Tape Cartridge interface

         There are 7 available SCSI targets and each target can support up to
         8 SCSI logical units.  The scsi driver restricts the total number of
         logical units that can be handled at once to some maximum, currently
         20.

         The minor device is encoded as tttdddmpppp; meanings of which are as
         follows:

         ttt selects the SCSI target.

         dddd selects the Logical Unit.

         m is the magic bit.

         pppp is the partition number.

         The last two entries are defined by the specific device driver.

         Scsi will only support access to one logical unit per SCSI target;
         thus bits 5-7 of the minor device number should always be zero.  This
         allows the use of SCSI hardware that does not decode the logical unit
         number.

         The scsi driver provides a generic ioctl interface so that the user
         can issue any SCSI command to a SCSI device.  The user process fills
         in the scsiioc structure specified below, found in
         /usr/include/sys/scsi.h.

         struct scsiioc {
               unsigned char     sjcb[10];
               unsigned char     sjcmdlength;
               unsigned char     sjdatadir;
               unsigned char     sjsdata[MAXSENSE];
               unsigned char     sjstatus;
               unsigned char     *sjdata;
               int         sjdatalength;
         };


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   scsi(7)                                                             scsi(7)


         The fields have the following meanings:

         sjcb[10]
               The command to be sent to the SCSI device, i.e those bytes
               transfer during the command phase.

         sjcmdlength
               Number of bytes in sj_cb above.

         sjdatadir
               Direction of data flow, 1 means the SCSI device will supply
               data to the user process during the data phase, a zero
               indicates that the kernel will copyout data from the user
               process and supply it to the SCSI device during the data phase.

         sjsdata[MAXSENSE]
               If the SCSI command failed, this array will contain the sense
               data returned from the SCSI device.

         sjstatus
               The sense byte, the data in the sj_sdata array is only valid if
               this byte is set to CHECKCOND. Any non-zero value indicates
               that the SCSI device rejected the command, or encounter some
               error during the processing of the command.

         sjdata
               The address where data will be copied to/from during the data
               phase.

         sjdatalength
               The number of data bytes to be supplied, or the size of the
               sj_data array.

         Currently only the hd interface supports the generic ioctl.

   SEE ALSO
         hd(7), tp(7).
















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