This is xnu-8019. See this file in:
/*
 * Copyright (c) 1998-2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */

#include <IOKit/IOLib.h>
#include <IOKit/IOInterleavedMemoryDescriptor.h>

#define super IOMemoryDescriptor
OSDefineMetaClassAndStructors(IOInterleavedMemoryDescriptor, IOMemoryDescriptor)

IOInterleavedMemoryDescriptor * IOInterleavedMemoryDescriptor::withCapacity(
	IOByteCount           capacity,
	IODirection           direction )
{
	//
	// Create a new IOInterleavedMemoryDescriptor.  The "buffer" will be made up
	// of several memory descriptors, that are to be chained end-to-end to make up
	// a single memory descriptor.
	//

	IOInterleavedMemoryDescriptor * me = new IOInterleavedMemoryDescriptor;

	if (me && !me->initWithCapacity(
		    /* capacity  */ capacity,
		    /* direction */ direction )) {
		me->release();
		me = NULL;
	}

	return me;
}

bool
IOInterleavedMemoryDescriptor::initWithCapacity(
	IOByteCount           capacity,
	IODirection           direction )
{
	//
	// Initialize an IOInterleavedMemoryDescriptor. The "buffer" will be made up
	// of several memory descriptors, that are to be chained end-to-end to make up
	// a single memory descriptor.
	//

	assert(capacity);

	// Ask our superclass' opinion.
	if (super::init() == false) {
		return false;
	}

	// Initialize our minimal state.

	_flags                  = direction;
#ifndef __LP64__
	_direction              = (IODirection) (_flags & kIOMemoryDirectionMask);
#endif /* !__LP64__ */
	_length                 = 0;
	_mappings               = NULL;
	_tag                    = 0;
	_descriptorCount        = 0;
	_descriptors            = IONew(IOMemoryDescriptor *, capacity);
	_descriptorOffsets      = IONewData(IOByteCount, capacity);
	_descriptorLengths      = IONewData(IOByteCount, capacity);

	if ((_descriptors == NULL) || (_descriptorOffsets == NULL) || (_descriptorLengths == NULL)) {
		return false;
	}

	_descriptorCapacity     = capacity;

	return true;
}

void
IOInterleavedMemoryDescriptor::clearMemoryDescriptors( IODirection direction )
{
	UInt32 index;

	for (index = 0; index < _descriptorCount; index++) {
		if (_descriptorPrepared) {
			_descriptors[index]->complete(getDirection());
		}

		_descriptors[index]->release();
		_descriptors[index] = NULL;

		_descriptorOffsets[index] = 0;
		_descriptorLengths[index] = 0;
	}

	if (direction != kIODirectionNone) {
		_flags = (_flags & ~kIOMemoryDirectionMask) | direction;
#ifndef __LP64__
		_direction = (IODirection) (_flags & kIOMemoryDirectionMask);
#endif /* !__LP64__ */
	}

	_descriptorCount = 0;
	_length = 0;
	_mappings = NULL;
	_tag = 0;
};

bool
IOInterleavedMemoryDescriptor::setMemoryDescriptor(
	IOMemoryDescriptor * descriptor,
	IOByteCount offset,
	IOByteCount length )
{
	if (_descriptorPrepared || (_descriptorCount == _descriptorCapacity)) {
		return false;
	}

	if ((offset + length) > descriptor->getLength()) {
		return false;
	}

//    if ( descriptor->getDirection() != getDirection() )
//        return false;

	descriptor->retain();
	_descriptors[_descriptorCount] = descriptor;
	_descriptorOffsets[_descriptorCount] = offset;
	_descriptorLengths[_descriptorCount] = length;

	_descriptorCount++;

	_length += length;

	return true;
}

void
IOInterleavedMemoryDescriptor::free()
{
	//
	// Free all of this object's outstanding resources.
	//

	if (_descriptors) {
		for (unsigned index = 0; index < _descriptorCount; index++) {
			_descriptors[index]->release();
		}

		if (_descriptors != NULL) {
			IODelete(_descriptors, IOMemoryDescriptor *, _descriptorCapacity);
		}

		if (_descriptorOffsets != NULL) {
			IODeleteData(_descriptorOffsets, IOByteCount, _descriptorCapacity);
		}

		if (_descriptorLengths != NULL) {
			IODeleteData(_descriptorLengths, IOByteCount, _descriptorCapacity);
		}
	}

	super::free();
}

IOReturn
IOInterleavedMemoryDescriptor::prepare(IODirection forDirection)
{
	//
	// Prepare the memory for an I/O transfer.
	//
	// This involves paging in the memory and wiring it down for the duration
	// of the transfer.  The complete() method finishes the processing of the
	// memory after the I/O transfer finishes.
	//

	unsigned index;
	IOReturn status = kIOReturnSuccess;
	IOReturn statusUndo;

	if (forDirection == kIODirectionNone) {
		forDirection = getDirection();
	}

	for (index = 0; index < _descriptorCount; index++) {
		status = _descriptors[index]->prepare(forDirection);
		if (status != kIOReturnSuccess) {
			break;
		}
	}

	if (status != kIOReturnSuccess) {
		for (unsigned indexUndo = 0; indexUndo < index; indexUndo++) {
			statusUndo = _descriptors[index]->complete(forDirection);
			assert(statusUndo == kIOReturnSuccess);
		}
	}

	if (status == kIOReturnSuccess) {
		_descriptorPrepared = true;
	}

	return status;
}

IOReturn
IOInterleavedMemoryDescriptor::complete(IODirection forDirection)
{
	//
	// Complete processing of the memory after an I/O transfer finishes.
	//
	// This method shouldn't be called unless a prepare() was previously issued;
	// the prepare() and complete() must occur in pairs, before and after an I/O
	// transfer.
	//

	IOReturn status;
	IOReturn statusFinal = kIOReturnSuccess;

	if (forDirection == kIODirectionNone) {
		forDirection = getDirection();
	}

	for (unsigned index = 0; index < _descriptorCount; index++) {
		status = _descriptors[index]->complete(forDirection);
		if (status != kIOReturnSuccess) {
			statusFinal = status;
		}
		assert(status == kIOReturnSuccess);
	}

	_descriptorPrepared = false;

	return statusFinal;
}

addr64_t
IOInterleavedMemoryDescriptor::getPhysicalSegment(
	IOByteCount   offset,
	IOByteCount * length,
	IOOptionBits  options )
{
	//
	// This method returns the physical address of the byte at the given offset
	// into the memory,  and optionally the length of the physically contiguous
	// segment from that offset.
	//

	addr64_t pa;

	assert(offset <= _length);

	for (unsigned index = 0; index < _descriptorCount; index++) {
		if (offset < _descriptorLengths[index]) {
			pa = _descriptors[index]->getPhysicalSegment(_descriptorOffsets[index] + offset, length, options);
			if ((_descriptorLengths[index] - offset) < *length) {
				*length = _descriptorLengths[index] - offset;
			}
			return pa;
		}
		offset -= _descriptorLengths[index];
	}

	if (length) {
		*length = 0;
	}

	return 0;
}