trusty (4) pass.4freebsd.gz

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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.