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     pass — CAM application passthrough driver


     device pass


     The pass driver provides a way for userland applications to issue CAM
     CCBs to the kernel.

     Since the pass driver allows direct access to the CAM subsystem, system
     administrators should exercise caution when granting access to this
     driver.  If used improperly, this driver can allow userland applications
     to crash a machine or cause data loss.

     The pass driver attaches to every SCSI device found in the system.  Since
     it attaches to every device, it provides a generic means of accessing
     SCSI devices, and allows the user to access devices which have no
     "standard" peripheral driver associated with them.


     It is only necessary to configure one pass device in the kernel; pass
     devices are automatically allocated as SCSI devices are found.


     CAMIOCOMMAND     This ioctl takes most kinds of CAM CCBs and passes them
                      through to the CAM transport layer for action.  Note
                      that some CCB types are not allowed through the
                      passthrough device, and must be sent through the xpt(4)
                      device instead.  Some examples of xpt-only CCBs are
                      XPT_SCAN_BUS, XPT_DEV_MATCH, XPT_RESET_BUS,
                      XPT_SCAN_LUN, XPT_ENG_INQ, and XPT_ENG_EXEC.  These CCB
                      types have various attributes that make it illogical or
                      impossible to service them through the passthrough

     CAMGETPASSTHRU   This ioctl takes an XPT_GDEVLIST CCB, and returns the
                      passthrough device corresponding to the device in
                      question.  Although this ioctl is available through the
                      pass driver, it is of limited use, since the caller must
                      already know that the device in question is a
                      passthrough device if they are issuing this ioctl.  It
                      is probably more useful to issue this ioctl through the
                      xpt(4) device.


     /dev/passn  Character device nodes for the pass driver.  There should be
                 one of these for each device accessed through the CAM




     cam(3), cam(4), cam_cdbparse(3), xpt(4), camcontrol(8)


     The CAM passthrough driver first appeared in FreeBSD 3.0.


     Kenneth Merry ⟨


     It might be nice to have a way to asynchronously send CCBs through the
     passthrough driver.  This would probably require some sort of read/write
     interface or an asynchronous ioctl interface.