PASS(4)                                                    BSD Kernel Interfaces Manual                                                    PASS(4)

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 access-
     ing 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.

BSD                                                              October 10, 1998                                                              BSD