iokit/IOKit/IOMemoryDescriptor.h

306     @param withDirection An I/O direction to be associated with the descriptor, which may affect the operation of the prepare and complete methods on some architectures.
317                                             task_t       withTask) APPLE_KEXT_DEPRECATED; /* use withAddressRange() and prepare() instead */
325     @param withDirection An I/O direction to be associated with the descriptor, which may affect the operation of the prepare and complete methods on some architectures.
347         kIOMemoryDirectionMask (options:direction)	This nibble indicates the I/O direction to be associated with the descriptor, which may affect the operation of the prepare and complete methods on some architectures.
363         kIOMemoryDirectionMask (options:direction)	This nibble indicates the I/O direction to be associated with the descriptor, which may affect the operation of the prepare and complete methods on some architectures.
388         kIOMemoryDirectionMask (options:direction)	This nibble indicates the I/O direction to be associated with the descriptor, which may affect the operation of the prepare and complete methods on some architectures.
519 /*! @function prepare
521     @discussion This involves paging in the memory, if necessary, and wiring it down for the duration of the transfer.  The complete() method completes the processing of the memory after the I/O transfer finishes.  Note that the prepare call is not thread safe and it is expected that the client will more easily be able to guarantee single threading a particular memory descriptor.
525     virtual IOReturn prepare(IODirection forDirection = kIODirectionNone) = 0;
529     @discussion This method should not be called unless a prepare was previously issued; the prepare() and complete() must occur in pairs, before and after an I/O transfer involving pageable memory.  In 10.3 or greater systems the direction argument to complete is not longer respected.  The direction is totally determined at prepare() time.
963     virtual IOReturn prepare(IODirection forDirection = kIODirectionNone);