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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.