Man

Command Section
PASS(4)                FreeBSD 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 and ATA device found in the
     system.  Since it attaches to every device, it provides a generic means
     of accessing SCSI and ATA 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 and ATA devices are found.

IOCTLS
     CAMIOCOMMAND union ccb *
            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.

            If the user would like the kernel to do error recovery, the
            CAM_PASS_ERR_RECOVER flag must be set on the CCB, and the
            retry_count field set to the number of retries.

     CAMGETPASSTHRU union ccb *
            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.

     CAMIOQUEUE union ccb *
            Queue a CCB to the pass driver to be executed asynchronously.  The
            caller may use select(2), poll(2) or kevent(2) to receive
            notification when the CCB has completed.

            This ioctl takes most CAM CCBs, but some CCB types are not allowed
            through the pass 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.

            Although the CAMIOQUEUE ioctl is not defined to take an argument,
            it does require a pointer to a union ccb.  It is not defined to
            take an argument to avoid an extra malloc and copy inside the
            generic ioctl(2) handler.

            The completed CCB will be returned via the CAMIOGET ioctl.  An
            error will only be returned from the CAMIOQUEUE ioctl if there is
            an error allocating memory for the request or copying memory from
            userland.  All other errors will be reported as standard CAM CCB
            status errors.  Since the CCB is not copied back to the user
            process from the pass driver in the CAMIOQUEUE ioctl, the user's
            passed-in CCB will not be modfied.  This is the case even with
            immediate CCBs.  Instead, the completed CCB must be retrieved via
            the CAMIOGET ioctl and the status examined.

            Multiple CCBs may be queued via the CAMIOQUEUE ioctl at any given
            time, and they may complete in a different order than the order
            that they were submitted.  The caller must take steps to identify
            CCBs that are queued and completed.  The periph_priv structure
            inside struct ccb_hdr is available for userland use with the
            CAMIOQUEUE and CAMIOGET ioctls, and will be preserved across
            calls.  Also, the periph_links linked list pointers inside struct
            ccb_hdr are available for userland use with the CAMIOQUEUE and
            CAMIOGET ioctls and will be preserved across calls.

            If the user would like the kernel to do error recovery, the
            CAM_PASS_ERR_RECOVER flag must be set on the CCB, and the
            retry_count field set to the number of retries.

     CAMIOGET union ccb *
            Retrieve completed CAM CCBs queued via the CAMIOQUEUE ioctl.  An
            error will only be returned from the CAMIOGET ioctl if the pass
            driver fails to copy data to the user process or if there are no
            completed CCBs available to retrieve.  If no CCBs are available to
            retrieve, errno will be set to ENOENT.

            All other errors will be reported as standard CAM CCB status
            errors.

            Although the CAMIOGET ioctl is not defined to take an argument, it
            does require a pointer to a union ccb.  It is not defined to take
            an argument to avoid an extra malloc and copy inside the generic
            ioctl(2) handler.

            The pass driver will report via select(2), poll(2) or kevent(2)
            when a CCB has completed.  One CCB may be retrieved per CAMIOGET
            call.  CCBs may be returned in an order different than the order
            they were submitted.  So the caller should use the periph_priv
            area inside the CCB header to store pointers to identifying
            information.

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
     kqueue(2), poll(2), select(2), cam(3), cam_cdbparse(3), cam(4), cd(4),
     ctl(4), da(4), sa(4), xpt(4), camcontrol(8), camdd(8)

HISTORY
     The CAM passthrough driver first appeared in FreeBSD 3.0.

AUTHORS
     Kenneth Merry <[email protected]>

FreeBSD 11.1-RELEASE-p4           May 3, 2017          FreeBSD 11.1-RELEASE-p4
Command Section