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SCSI(4)                  BSD Kernel Interfaces Manual                  SCSI(4)

     scsi -- SCSI system

     cd* at scsibus?
     ch* at scsibus?
     safte* at scsibus?
     sd* at scsibus?
     ses* at scsibus?
     st* at scsibus?
     uk* at scsibus?

     # multipath support
     emc* at scsibus?
     hds* at scsibus?
     rdac* at scsibus?
     sym* at scsibus?

     The SCSI system provides a uniform and modular system for the implementa-
     tion of drivers to control various SCSI devices, and to utilize different
     SCSI host adapters through host adapter drivers.  When the system probes
     the SCSI buses, it attaches any devices it finds to the appropriate driv-
     ers.  If no driver seems appropriate, then it attaches the device to the
     uk (unknown) driver so that user level SCSI ioctls may still be performed
     against the device.

     The option SCSIDEBUG enables the debug ioctl.

     All devices and the SCSI buses support boot time allocation so that an
     upper number of devices and controllers does not need to be configured;
     sd* at scsibus? will suffice for any number of disk drivers.

     The devices are either wired so they appear as a particular device unit
     or counted so that they appear as the next available unused unit.

     To configure a driver in the kernel without wiring down the device use a
     config line similar to ch* at scsibus? to include the changer driver.

     To wire down a unit use a config line similar to ch1 at scsibus0 target 4
     lun 0 to assign changer 1 as the changer with SCSI ID 4, SCSI logical
     unit 0 on SCSI bus 0.  Individual scsibuses can be wired down to specific
     controllers with a config line similar to scsibus0 at ahc0 which assigns
     SCSI bus 0 to the first unit using the ahc driver.  For controllers sup-
     porting more than one bus, the particular bus can be specified as in
     scsibus3 at ahc1 bus 1 which assigns scsibus 1 to the second bus probed
     on the ahc1 device.

     When there is a mixture of wired down and counted devices then the count-
     ing begins with the first non-wired down unit for a particular type.
     That is, if a disk is wired down as sd1 at scsibus?, then the first non-
     wired disk shall come on line as sd2.

     There are a number of ioctls that work on any SCSI device.  They are
     defined in <sys/scsiio.h> and can be applied against any SCSI device that
     permits them.  For the tape, it must be applied against the control
     device.  See the manual page for each device type for more information
     about how generic SCSI ioctls may be applied to a specific device.

     SCIOCRESET      Reset a device.

     SCIOCDEBUG int *
                     Turn on debugging.  All SCSI operations originating from
                     this device's driver will be traced to the console, along
                     with other information.  Debugging is controlled by four
                     bits, described in the header file.  If no debugging is
                     configured into the kernel, debugging will have no
                     effect.  SCSI debugging is controlled by the configura-
                     tion option SCSIDEBUG.

     SCIOCCOMMAND scsireq_t *
                     Take a SCSI command and data from a user process and
                     apply them to the SCSI device.  Return all status infor-
                     mation and return data to the process.  The ioctl will
                     return a successful status even if the device rejected
                     the command.  As all status is returned to the user, it
                     is up to the user process to examine this information to
                     decide the success of the command.

     SCIOCIDENTIFY struct scsi_addr *
                     Ask the driver what its bus, target and lun are.  In
                     addition, the device type, ATAPI or SCSI, is returned.

     The system allows common device drivers to work through many different
     types of adapters.  The adapters take requests from the upper layers and
     do all I/O between the SCSI bus and the system.  The maximum size of a
     transfer is governed by the adapter.  Most adapters can transfer 64KB in
     a single operation, and many can transfer larger amounts.

     When the kernel is compiled with option SCSIDEBUG, the SCIOCDEBUG ioctl
     can be used to enable various amounts of tracing information on any spe-
     cific device.  Devices not being traced will not produce trace informa-
     tion.  The four bits that make up the debug level each control certain
     types of debugging information.

     Bit 0  shows all SCSI bus operations including SCSI commands, error
            information and the first 48 bytes of any data transferred.

     Bit 1  shows routines called.

     Bit 2  shows information about what branches are taken and often some of
            the return values of functions.

     Bit 3  shows more detailed information including DMA scatter-gather logs.

     cd(4), ch(4), emc(4), hds(4), intro(4), mpath(4), rdac(4), safte(4),
     sd(4), ses(4), st(4), sym(4), uk(4), scsi(8)

     This scsi system appeared in MACH 2.5 at TRW.

BSD                             March 28, 2017                             BSD