NAME

       pass — CAM application passthrough driver

SYNOPSIS

       device pass

DESCRIPTION

       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.

KERNEL CONFIGURATION

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

IOCTLS

       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 interface.

       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.

FILES

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

DIAGNOSTICS

       None.

SEE ALSO

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

HISTORY

       The CAM passthrough driver first appeared in FreeBSD 3.0.

AUTHORS

       Kenneth Merry <ken@FreeBSD.org>

BUGS

       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.

Debian                                          October 10, 1998                                         PASS(4)