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PASS(4)               DragonFly Kernel Interfaces Manual               PASS(4)


NAME

     pass -- CAM application passthrough driver


SYNOPSIS

     device pass
     device pass2 at scbus0 target 3 unit 0


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 "stan-
     dard" 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 var-
                     ious 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 ques-
                     tion.  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're 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 subsys-
                 tem.


DIAGNOSTICS

     None.


SEE ALSO

     cam(3), 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.

DragonFly 3.5                  October 10, 1998                  DragonFly 3.5

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