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Device driver function 19h      IOCTL Query             b   c

    IOCTL Query determines whether a given generic IOCTL function
    (minor code) is supported by the driver.

    This function can be used both for block and character device
    drivers.

    ------------------------------------------------------------------

    DOS calls this function only if bit 7 is set in the dhAttributes
    field of the DeviceHeader structure for the driver.

    ------------------------------------------------------------------

    giUnit
    Specifies the device the request is for. This field is used for
    block device drivers only.


    giStatus
    Receives the status of the query. If the driver does not support
    the given generic IOCTL function, it must set the error and done
    bits (bits 15 and 8) and set the low-order byte to error value 03h
    (Unknown Function). Otherwise, it must set the done bit (bit 8).


    giCategory
    Specifies the device category of the generic IOCTL function to be
    checked.


    giMinorCode
    Specifies the minor code of the generic IOCTL function to be
    checked.


    giIOCTLData
    This field is not used by this function and must not be changed.