file_systems/bfs/BlockAllocator.cpp

/*
 * Copyright 2001-2009, Axel Dörfler, axeld@pinc-software.de.
 * This file may be used under the terms of the MIT License.
 */

//! block bitmap handling and allocation policies


#include "BlockAllocator.h"

#include "bfs_control.h"
#include "BPlusTree.h"
#include "Debug.h"
#include "Inode.h"
#include "Volume.h"


// Things the BlockAllocator should do:

// - find a range of blocks of a certain size nearby a specific position
// - allocating an unsharp range of blocks for pre-allocation
// - free blocks
// - know how to deal with each allocation, special handling for directories,
//   files, symlinks, etc. (type sensitive allocation policies)

// What makes the code complicated is the fact that we are not just reading
// in the whole bitmap and operate on that in memory - e.g. a 13 GB partition
// with a block size of 2048 bytes already has a 800kB bitmap, and the size
// of partitions will grow even more - so that's not an option.
// Instead we are reading in every block when it's used - since an allocation
// group can span several blocks in the block bitmap, the AllocationBlock
// class is there to make handling those easier.

// The current implementation is only slightly optimized and could probably
// be improved a lot. Furthermore, the allocation policies used here should
// have some real world tests.

#if BFS_TRACING && !defined(BFS_SHELL)
namespace BFSBlockTracing {

class Allocate : public AbstractTraceEntry {
public:
	Allocate(block_run run)
		:
		fRun(run)
	{
		Initialized();
	}

	virtual void AddDump(TraceOutput& out)
	{
		out.Print("bfs:alloc %lu.%u.%u", fRun.AllocationGroup(),
			fRun.Start(), fRun.Length());
	}

	const block_run& Run() const { return fRun; }

private:
	block_run	fRun;
};

class Free : public AbstractTraceEntry {
public:
	Free(block_run run)
		:
		fRun(run)
	{
		Initialized();
	}

	virtual void AddDump(TraceOutput& out)
	{
		out.Print("bfs:free %lu.%u.%u", fRun.AllocationGroup(),
			fRun.Start(), fRun.Length());
	}

	const block_run& Run() const { return fRun; }

private:
	block_run	fRun;
};


static uint32
checksum(const uint8* data, size_t size)
{
	const uint32* data4 = (const uint32*)data;
	uint32 sum = 0;
	while (size >= 4) {
		sum += *data4;
		data4++;
		size -= 4;
	}
	return sum;
}


class Block : public AbstractTraceEntry {
public:
	Block(const char* label, off_t blockNumber, const uint8* data,
			size_t size, uint32 start = 0, uint32 length = 0)
		:
		fBlock(blockNumber),
		fData(data),
		fStart(start),
		fLength(length),
		fLabel(label)
	{
		fSum = checksum(data, size);
		Initialized();
	}

	virtual void AddDump(TraceOutput& out)
	{
		out.Print("bfs:%s: block %Ld (%p), sum %lu, s/l %lu/%lu", fLabel,
			fBlock, fData, fSum, fStart, fLength);
	}

private:
	off_t		fBlock;
	const uint8	*fData;
	uint32		fStart;
	uint32		fLength;
	uint32		fSum;
	const char*	fLabel;
};


class BlockChange : public AbstractTraceEntry {
public:
	BlockChange(const char* label, int32 block, uint32 oldData, uint32 newData)
		:
		fBlock(block),
		fOldData(oldData),
		fNewData(newData),
		fLabel(label)
	{
		Initialized();
	}

	virtual void AddDump(TraceOutput& out)
	{
		out.Print("bfs:%s: block %ld, %08lx -> %08lx", fLabel,
			fBlock, fOldData, fNewData);
	}

private:
	int32		fBlock;
	uint32		fOldData;
	uint32		fNewData;
	const char*	fLabel;
};

}	// namespace BFSBlockTracing

#	define T(x) new(std::nothrow) BFSBlockTracing::x;
#else
#	define T(x) ;
#endif

#ifdef DEBUG_ALLOCATION_GROUPS
#	define CHECK_ALLOCATION_GROUP(group) _CheckGroup(group)
#else
#	define CHECK_ALLOCATION_GROUP(group) ;
#endif


struct check_cookie {
	check_cookie() {}

	block_run			current;
	Inode*				parent;
	mode_t				parent_mode;
	Stack<block_run>	stack;
	TreeIterator*		iterator;
};


class AllocationBlock : public CachedBlock {
public:
	AllocationBlock(Volume* volume);

	inline void Allocate(uint16 start, uint16 numBlocks);
	inline void Free(uint16 start, uint16 numBlocks);
	inline bool IsUsed(uint16 block);

	status_t SetTo(AllocationGroup& group, uint16 block);
	status_t SetToWritable(Transaction& transaction, AllocationGroup& group,
		uint16 block);

	uint32 NumBlockBits() const { return fNumBits; }
	uint32& Block(int32 index) { return ((uint32*)fBlock)[index]; }
	uint8* Block() const { return (uint8*)fBlock; }

private:
	uint32	fNumBits;
#ifdef DEBUG
	bool	fWritable;
#endif
};


class AllocationGroup {
public:
	AllocationGroup();

	void AddFreeRange(int32 start, int32 blocks);
	bool IsFull() const { return fFreeBits == 0; }

	status_t Allocate(Transaction& transaction, uint16 start, int32 length);
	status_t Free(Transaction& transaction, uint16 start, int32 length);

	uint32 NumBits() const { return fNumBits; }
	uint32 NumBlocks() const { return fNumBlocks; }
	int32 Start() const { return fStart; }

private:
	friend class BlockAllocator;

	uint32	fNumBits;
	uint32	fNumBlocks;
	int32	fStart;
	int32	fFirstFree;
	int32	fFreeBits;

	int32	fLargestStart;
	int32	fLargestLength;
	bool	fLargestValid;
};


AllocationBlock::AllocationBlock(Volume* volume)
	: CachedBlock(volume)
{
}


status_t
AllocationBlock::SetTo(AllocationGroup& group, uint16 block)
{
	// 8 blocks per byte
	fNumBits = fVolume->BlockSize() << 3;
	// the last group may have less bits than the others
	if ((block + 1) * fNumBits > group.NumBits())
		fNumBits = group.NumBits() % fNumBits;

#ifdef DEBUG
	fWritable = false;
#endif
	return CachedBlock::SetTo(group.Start() + block) != NULL ? B_OK : B_ERROR;
}


status_t
AllocationBlock::SetToWritable(Transaction& transaction, AllocationGroup& group,
	uint16 block)
{
	// 8 blocks per byte
	fNumBits = fVolume->BlockSize() << 3;
	// the last group may have less bits in the last block
	if ((block + 1) * fNumBits > group.NumBits())
		fNumBits = group.NumBits() % fNumBits;

#ifdef DEBUG
	fWritable = true;
#endif
	return CachedBlock::SetToWritable(transaction, group.Start() + block)
		!= NULL ? B_OK : B_ERROR;
}


bool
AllocationBlock::IsUsed(uint16 block)
{
	if (block > fNumBits)
		return true;

	// the block bitmap is accessed in 32-bit blocks
	return Block(block >> 5) & HOST_ENDIAN_TO_BFS_INT32(1UL << (block % 32));
}


void
AllocationBlock::Allocate(uint16 start, uint16 numBlocks)
{
	ASSERT(start < fNumBits);
	ASSERT(uint32(start + numBlocks) <= fNumBits);
#ifdef DEBUG
	ASSERT(fWritable);
#endif

	T(Block("b-alloc-in", fBlockNumber, fBlock, fVolume->BlockSize(),
		start, numBlocks));

	int32 block = start >> 5;

	while (numBlocks > 0) {
		uint32 mask = 0;
		for (int32 i = start % 32; i < 32 && numBlocks; i++, numBlocks--)
			mask |= 1UL << i;

		T(BlockChange("b-alloc", block, Block(block),
			Block(block) | HOST_ENDIAN_TO_BFS_INT32(mask)));

#if KDEBUG
		// check for already set blocks
		if (HOST_ENDIAN_TO_BFS_INT32(mask) & ((uint32*)fBlock)[block]) {
			FATAL(("AllocationBlock::Allocate(): some blocks are already "
				"allocated, start = %u, numBlocks = %u\n", start, numBlocks));
			panic("blocks already set!");
		}
#endif

		Block(block++) |= HOST_ENDIAN_TO_BFS_INT32(mask);
		start = 0;
	}
	T(Block("b-alloc-out", fBlockNumber, fBlock, fVolume->BlockSize(),
		start, numBlocks));
}


void
AllocationBlock::Free(uint16 start, uint16 numBlocks)
{
	ASSERT(start < fNumBits);
	ASSERT(uint32(start + numBlocks) <= fNumBits);
#ifdef DEBUG
	ASSERT(fWritable);
#endif

	int32 block = start >> 5;

	while (numBlocks > 0) {
		uint32 mask = 0;
		for (int32 i = start % 32; i < 32 && numBlocks; i++, numBlocks--)
			mask |= 1UL << (i % 32);

		T(BlockChange("b-free", block, Block(block),
			Block(block) & HOST_ENDIAN_TO_BFS_INT32(~mask)));

		Block(block++) &= HOST_ENDIAN_TO_BFS_INT32(~mask);
		start = 0;
	}
}


//	#pragma mark -


/*!	The allocation groups are created and initialized in
	BlockAllocator::Initialize() and BlockAllocator::InitializeAndClearBitmap()
	respectively.
*/
AllocationGroup::AllocationGroup()
	:
	fFirstFree(-1),
	fFreeBits(0),
	fLargestValid(false)
{
}


void
AllocationGroup::AddFreeRange(int32 start, int32 blocks)
{
	//D(if (blocks > 512)
	//	PRINT(("range of %ld blocks starting at %ld\n",blocks,start)));

	if (fFirstFree == -1)
		fFirstFree = start;

	if (!fLargestValid || fLargestLength < blocks) {
		fLargestStart = start;
		fLargestLength = blocks;
		fLargestValid = true;
	}

	fFreeBits += blocks;
}


/*!	Allocates the specified run in the allocation group.
	Doesn't check if the run is valid or already allocated partially, nor
	does it maintain the free ranges hints or the volume's used blocks count.
	It only does the low-level work of allocating some bits in the block bitmap.
	Assumes that the block bitmap lock is hold.
*/
status_t
AllocationGroup::Allocate(Transaction& transaction, uint16 start, int32 length)
{
	ASSERT(start + length <= (int32)fNumBits);

	// Update the allocation group info
	// TODO: this info will be incorrect if something goes wrong later
	// Note, the fFirstFree block doesn't have to be really free
	if (start == fFirstFree)
		fFirstFree = start + length;
	fFreeBits -= length;

	if (fLargestValid) {
		bool cut = false;
		if (fLargestStart == start) {
			// cut from start
			fLargestStart += length;
			fLargestLength -= length;
			cut = true;
		} else if (start > fLargestStart
			&& start < fLargestStart + fLargestLength) {
			// cut from end
			fLargestLength = start - fLargestStart;
			cut = true;
		}
		if (cut && (fLargestLength < fLargestStart
				|| fLargestLength
						< (int32)fNumBits - (fLargestStart + fLargestLength))) {
			// might not be the largest block anymore
			fLargestValid = false;
		}
	}

	Volume* volume = transaction.GetVolume();

	// calculate block in the block bitmap and position within
	uint32 bitsPerBlock = volume->BlockSize() << 3;
	uint32 block = start / bitsPerBlock;
	start = start % bitsPerBlock;

	AllocationBlock cached(volume);

	while (length > 0) {
		if (cached.SetToWritable(transaction, *this, block) < B_OK) {
			fLargestValid = false;
			RETURN_ERROR(B_IO_ERROR);
		}

		uint32 numBlocks = length;
		if (start + numBlocks > cached.NumBlockBits())
			numBlocks = cached.NumBlockBits() - start;

		cached.Allocate(start, numBlocks);

		length -= numBlocks;
		start = 0;
		block++;
	}

	return B_OK;
}


/*!	Frees the specified run in the allocation group.
	Doesn't check if the run is valid or was not completely allocated, nor
	does it maintain the free ranges hints or the volume's used blocks count.
	It only does the low-level work of freeing some bits in the block bitmap.
	Assumes that the block bitmap lock is hold.
*/
status_t
AllocationGroup::Free(Transaction& transaction, uint16 start, int32 length)
{
	ASSERT(start + length <= (int32)fNumBits);

	// Update the allocation group info
	// TODO: this info will be incorrect if something goes wrong later
	if (fFirstFree > start)
		fFirstFree = start;
	fFreeBits += length;

	// The range to be freed cannot be part of the valid largest range
	ASSERT(!fLargestValid || start + length <= fLargestStart
		|| start > fLargestStart);

	if (fLargestValid
		&& (start + length == fLargestStart
			|| fLargestStart + fLargestLength == start
			|| (start < fLargestStart && fLargestStart > fLargestLength)
			|| (start > fLargestStart
				&& (int32)fNumBits - (fLargestStart + fLargestLength)
						> fLargestLength))) {
		fLargestValid = false;
	}

	Volume* volume = transaction.GetVolume();

	// calculate block in the block bitmap and position within
	uint32 bitsPerBlock = volume->BlockSize() << 3;
	uint32 block = start / bitsPerBlock;
	start = start % bitsPerBlock;

	AllocationBlock cached(volume);

	while (length > 0) {
		if (cached.SetToWritable(transaction, *this, block) < B_OK)
			RETURN_ERROR(B_IO_ERROR);

		T(Block("free-1", block, cached.Block(), volume->BlockSize()));
		uint16 freeLength = length;
		if (uint32(start + length) > cached.NumBlockBits())
			freeLength = cached.NumBlockBits() - start;

		cached.Free(start, freeLength);

		length -= freeLength;
		start = 0;
		T(Block("free-2", block, cached.Block(), volume->BlockSize()));
		block++;
	}
	return B_OK;
}


//	#pragma mark -


BlockAllocator::BlockAllocator(Volume* volume)
	:
	fVolume(volume),
	fGroups(NULL),
	fCheckBitmap(NULL)
{
	mutex_init(&fLock, "bfs allocator");
}


BlockAllocator::~BlockAllocator()
{
	mutex_destroy(&fLock);
	delete[] fGroups;
}


status_t
BlockAllocator::Initialize(bool full)
{
	fNumGroups = fVolume->AllocationGroups();
	fBlocksPerGroup = fVolume->SuperBlock().BlocksPerAllocationGroup();
	fNumBlocks = (fVolume->NumBlocks() + fVolume->BlockSize() * 8 - 1)
		/ (fVolume->BlockSize() * 8);

	fGroups = new AllocationGroup[fNumGroups];
	if (fGroups == NULL)
		return B_NO_MEMORY;

	if (!full)
		return B_OK;

	mutex_lock(&fLock);
		// the lock will be released by the _Initialize() method

	thread_id id = spawn_kernel_thread((thread_func)BlockAllocator::_Initialize,
		"bfs block allocator", B_LOW_PRIORITY, this);
	if (id < B_OK)
		return _Initialize(this);

	mutex_transfer_lock(&fLock, id);

	return resume_thread(id);
}


status_t
BlockAllocator::InitializeAndClearBitmap(Transaction& transaction)
{
	status_t status = Initialize(false);
	if (status != B_OK)
		return status;

	uint32 numBits = 8 * fBlocksPerGroup * fVolume->BlockSize();
	uint32 blockShift = fVolume->BlockShift();

	uint32* buffer = (uint32*)malloc(numBits >> 3);
	if (buffer == NULL)
		RETURN_ERROR(B_NO_MEMORY);

	memset(buffer, 0, numBits >> 3);

	off_t offset = 1;
		// the bitmap starts directly after the super block

	// initialize the AllocationGroup objects and clear the on-disk bitmap

	for (int32 i = 0; i < fNumGroups; i++) {
		if (write_pos(fVolume->Device(), offset << blockShift, buffer,
				fBlocksPerGroup << blockShift) < B_OK)
			return B_ERROR;

		// the last allocation group may contain less blocks than the others
		if (i == fNumGroups - 1) {
			fGroups[i].fNumBits = fVolume->NumBlocks() - i * numBits;
			fGroups[i].fNumBlocks = 1 + ((fGroups[i].NumBits() - 1)
				>> (blockShift + 3));
		} else {
			fGroups[i].fNumBits = numBits;
			fGroups[i].fNumBlocks = fBlocksPerGroup;
		}
		fGroups[i].fStart = offset;
		fGroups[i].fFirstFree = fGroups[i].fLargestStart = 0;
		fGroups[i].fFreeBits = fGroups[i].fLargestLength = fGroups[i].fNumBits;
		fGroups[i].fLargestValid = true;

		offset += fBlocksPerGroup;
	}
	free(buffer);

	// reserve the boot block, the log area, and the block bitmap itself
	uint32 reservedBlocks = fVolume->Log().Start() + fVolume->Log().Length();

	if (fGroups[0].Allocate(transaction, 0, reservedBlocks) < B_OK) {
		FATAL(("could not allocate reserved space for block bitmap/log!\n"));
		return B_ERROR;
	}
	fVolume->SuperBlock().used_blocks
		= HOST_ENDIAN_TO_BFS_INT64(reservedBlocks);

	return B_OK;
}


status_t
BlockAllocator::_Initialize(BlockAllocator* allocator)
{
	// The lock must already be held at this point

	Volume* volume = allocator->fVolume;
	uint32 blocks = allocator->fBlocksPerGroup;
	uint32 blockShift = volume->BlockShift();
	off_t freeBlocks = 0;

	uint32* buffer = (uint32*)malloc(blocks << blockShift);
	if (buffer == NULL) {
		mutex_unlock(&allocator->fLock);
		RETURN_ERROR(B_NO_MEMORY);
	}

	AllocationGroup* groups = allocator->fGroups;
	off_t offset = 1;
	uint32 bitsPerGroup = 8 * (blocks << blockShift);
	int32 numGroups = allocator->fNumGroups;

	for (int32 i = 0; i < numGroups; i++) {
		if (read_pos(volume->Device(), offset << blockShift, buffer,
				blocks << blockShift) < B_OK)
			break;

		// the last allocation group may contain less blocks than the others
		if (i == numGroups - 1) {
			groups[i].fNumBits = volume->NumBlocks() - i * bitsPerGroup;
			groups[i].fNumBlocks = 1 + ((groups[i].NumBits() - 1)
				>> (blockShift + 3));
		} else {
			groups[i].fNumBits = bitsPerGroup;
			groups[i].fNumBlocks = blocks;
		}
		groups[i].fStart = offset;

		// finds all free ranges in this allocation group
		int32 start = -1, range = 0;
		int32 numBits = groups[i].fNumBits, bit = 0;
		int32 count = (numBits + 31) / 32;

		for (int32 k = 0; k < count; k++) {
			for (int32 j = 0; j < 32 && bit < numBits; j++, bit++) {
				if (buffer[k] & (1UL << j)) {
					// block is in use
					if (range > 0) {
						groups[i].AddFreeRange(start, range);
						range = 0;
					}
				} else if (range++ == 0) {
					// block is free, start new free range
					start = bit;
				}
			}
		}
		if (range)
			groups[i].AddFreeRange(start, range);

		freeBlocks += groups[i].fFreeBits;

		offset += blocks;
	}
	free(buffer);

	// check if block bitmap and log area are reserved
	uint32 reservedBlocks = volume->Log().Start() + volume->Log().Length();

	if (allocator->CheckBlocks(0, reservedBlocks) != B_OK) {
		if (volume->IsReadOnly()) {
			FATAL(("Space for block bitmap or log area is not reserved "
				"(volume is mounted read-only)!\n"));
		} else {
			Transaction transaction(volume, 0);
			if (groups[0].Allocate(transaction, 0, reservedBlocks) != B_OK) {
				FATAL(("Could not allocate reserved space for block "
					"bitmap/log!\n"));
				volume->Panic();
			} else {
				transaction.Done();
				FATAL(("Space for block bitmap or log area was not "
					"reserved!\n"));
			}
		}
	}

	off_t usedBlocks = volume->NumBlocks() - freeBlocks;
	if (volume->UsedBlocks() != usedBlocks) {
		// If the disk in a dirty state at mount time, it's
		// normal that the values don't match
		INFORM(("volume reports %" B_PRIdOFF " used blocks, correct is %"
			B_PRIdOFF "\n", volume->UsedBlocks(), usedBlocks));
		volume->SuperBlock().used_blocks = HOST_ENDIAN_TO_BFS_INT64(usedBlocks);
	}

	mutex_unlock(&allocator->fLock);
	return B_OK;
}


void
BlockAllocator::Uninitialize()
{
	// We only have to make sure that the initializer thread isn't running
	// anymore.
	mutex_lock(&fLock);
}


/*!	Tries to allocate between \a minimum, and \a maximum blocks starting
	at group \a groupIndex with offset \a start. The resulting allocation
	is put into \a run.

	The number of allocated blocks is always a multiple of \a minimum which
	has to be a power of two value.
*/
status_t
BlockAllocator::AllocateBlocks(Transaction& transaction, int32 groupIndex,
	uint16 start, uint16 maximum, uint16 minimum, block_run& run)
{
	if (maximum == 0)
		return B_BAD_VALUE;

	FUNCTION_START(("group = %ld, start = %u, maximum = %u, minimum = %u\n",
		groupIndex, start, maximum, minimum));

	AllocationBlock cached(fVolume);
	MutexLocker lock(fLock);

	uint32 bitsPerFullBlock = fVolume->BlockSize() << 3;

	// Find the block_run that can fulfill the request best
	int32 bestGroup = -1;
	int32 bestStart = -1;
	int32 bestLength = -1;

	for (int32 i = 0; i < fNumGroups + 1; i++, groupIndex++, start = 0) {
		groupIndex = groupIndex % fNumGroups;
		AllocationGroup& group = fGroups[groupIndex];

		CHECK_ALLOCATION_GROUP(groupIndex);

		if (start >= group.NumBits() || group.IsFull())
			continue;

		// The wanted maximum is smaller than the largest free block in the
		// group or already smaller than the minimum

		if (start < group.fFirstFree)
			start = group.fFirstFree;

		if (group.fLargestValid) {
			if (group.fLargestLength < bestLength)
				continue;

			if (group.fLargestStart >= start) {
				if (group.fLargestLength >= bestLength) {
					bestGroup = groupIndex;
					bestStart = group.fLargestStart;
					bestLength = group.fLargestLength;

					if (bestLength >= maximum)
						break;
				}

				// We know everything about this group we have to, let's skip
				// to the next
				continue;
			}
		}

		// There may be more than one block per allocation group - and
		// we iterate through it to find a place for the allocation.
		// (one allocation can't exceed one allocation group)

		uint32 block = start / (fVolume->BlockSize() << 3);
		int32 currentStart = 0, currentLength = 0;
		int32 groupLargestStart = -1;
		int32 groupLargestLength = -1;
		int32 currentBit = start;
		bool canFindGroupLargest = start == 0;

		for (; block < group.NumBlocks(); block++) {
			if (cached.SetTo(group, block) < B_OK)
				RETURN_ERROR(B_ERROR);

			T(Block("alloc-in", group.Start() + block, cached.Block(),
				fVolume->BlockSize(), groupIndex, currentStart));

			// find a block large enough to hold the allocation
			for (uint32 bit = start % bitsPerFullBlock;
					bit < cached.NumBlockBits(); bit++) {
				if (!cached.IsUsed(bit)) {
					if (currentLength == 0) {
						// start new range
						currentStart = currentBit;
					}

					// have we found a range large enough to hold numBlocks?
					if (++currentLength >= maximum) {
						bestGroup = groupIndex;
						bestStart = currentStart;
						bestLength = currentLength;
						break;
					}
				} else {
					if (currentLength) {
						// end of a range
						if (currentLength > bestLength) {
							bestGroup = groupIndex;
							bestStart = currentStart;
							bestLength = currentLength;
						}
						if (currentLength > groupLargestLength) {
							groupLargestStart = currentStart;
							groupLargestLength = currentLength;
						}
						currentLength = 0;
					}
					if ((int32)group.NumBits() - currentBit
							<= groupLargestLength) {
						// We can't find a bigger block in this group anymore,
						// let's skip the rest.
						block = group.NumBlocks();
						break;
					}
				}
				currentBit++;
			}

			T(Block("alloc-out", block, cached.Block(),
				fVolume->BlockSize(), groupIndex, currentStart));

			if (bestLength >= maximum) {
				canFindGroupLargest = false;
				break;
			}

			// start from the beginning of the next block
			start = 0;
		}

		if (currentBit == (int32)group.NumBits()) {
			if (currentLength > bestLength) {
				bestGroup = groupIndex;
				bestStart = currentStart;
				bestLength = currentLength;
			}
			if (canFindGroupLargest && currentLength > groupLargestLength) {
				groupLargestStart = currentStart;
				groupLargestLength = currentLength;
			}
		}

		if (canFindGroupLargest && !group.fLargestValid
			&& groupLargestLength >= 0) {
			group.fLargestStart = groupLargestStart;
			group.fLargestLength = groupLargestLength;
			group.fLargestValid = true;
		}

		if (bestLength >= maximum)
			break;
	}

	// If we found a suitable range, mark the blocks as in use, and
	// write the updated block bitmap back to disk
	if (bestLength < minimum)
		return B_DEVICE_FULL;

	if (bestLength > maximum)
		bestLength = maximum;
	else if (minimum > 1) {
		// make sure bestLength is a multiple of minimum
		bestLength = round_down(bestLength, minimum);
	}

	if (fGroups[bestGroup].Allocate(transaction, bestStart, bestLength) != B_OK)
		RETURN_ERROR(B_IO_ERROR);

	CHECK_ALLOCATION_GROUP(bestGroup);

	run.allocation_group = HOST_ENDIAN_TO_BFS_INT32(bestGroup);
	run.start = HOST_ENDIAN_TO_BFS_INT16(bestStart);
	run.length = HOST_ENDIAN_TO_BFS_INT16(bestLength);

	fVolume->SuperBlock().used_blocks
		= HOST_ENDIAN_TO_BFS_INT64(fVolume->UsedBlocks() + bestLength);
		// We are not writing back the disk's super block - it's
		// either done by the journaling code, or when the disk
		// is unmounted.
		// If the value is not correct at mount time, it will be
		// fixed anyway.

	// We need to flush any remaining blocks in the new allocation to make sure
	// they won't interfere with the file cache.
	block_cache_discard(fVolume->BlockCache(), fVolume->ToBlock(run),
		run.Length());

	T(Allocate(run));
	return B_OK;
}


status_t
BlockAllocator::AllocateForInode(Transaction& transaction,
	const block_run* parent, mode_t type, block_run& run)
{
	// Apply some allocation policies here (AllocateBlocks() will break them
	// if necessary) - we will start with those described in Dominic Giampaolo's
	// "Practical File System Design", and see how good they work

	// Files are going in the same allocation group as its parent,
	// sub-directories will be inserted 8 allocation groups after
	// the one of the parent
	uint16 group = parent->AllocationGroup();
	if ((type & (S_DIRECTORY | S_INDEX_DIR | S_ATTR_DIR)) == S_DIRECTORY)
		group += 8;

	return AllocateBlocks(transaction, group, 0, 1, 1, run);
}


status_t
BlockAllocator::Allocate(Transaction& transaction, Inode* inode,
	off_t numBlocks, block_run& run, uint16 minimum)
{
	if (numBlocks <= 0)
		return B_ERROR;

	// one block_run can't hold more data than there is in one allocation group
	if (numBlocks > fGroups[0].NumBits())
		numBlocks = fGroups[0].NumBits();

	// since block_run.length is uint16, the largest number of blocks that
	// can be covered by a block_run is 65535
	// TODO: if we drop compatibility, couldn't we do this any better?
	// There are basically two possibilities:
	// a) since a length of zero doesn't have any sense, take that for 65536 -
	//    but that could cause many problems (bugs) in other areas
	// b) reduce the maximum amount of blocks per block_run, so that the
	//    remaining number of free blocks can be used in a useful manner
	//    (like 4 blocks) - but that would also reduce the maximum file size
	// c) have BlockRun::Length() return (length + 1).
	if (numBlocks > MAX_BLOCK_RUN_LENGTH)
		numBlocks = MAX_BLOCK_RUN_LENGTH;

	// Apply some allocation policies here (AllocateBlocks() will break them
	// if necessary)
	uint16 group = inode->BlockRun().AllocationGroup();
	uint16 start = 0;

	// Are there already allocated blocks? (then just try to allocate near the
	// last one)
	if (inode->Size() > 0) {
		const data_stream& data = inode->Node().data;
		// TODO: we currently don't care for when the data stream
		// is already grown into the indirect ranges
		if (data.max_double_indirect_range == 0
			&& data.max_indirect_range == 0) {
			// Since size > 0, there must be a valid block run in this stream
			int32 last = 0;
			for (; last < NUM_DIRECT_BLOCKS - 1; last++)
				if (data.direct[last + 1].IsZero())
					break;

			group = data.direct[last].AllocationGroup();
			start = data.direct[last].Start() + data.direct[last].Length();
		}
	} else if (inode->IsContainer() || inode->IsSymLink()) {
		// directory and symbolic link data will go in the same allocation
		// group as the inode is in but after the inode data
		start = inode->BlockRun().Start();
	} else {
		// file data will start in the next allocation group
		group = inode->BlockRun().AllocationGroup() + 1;
	}

	return AllocateBlocks(transaction, group, start, numBlocks, minimum, run);
}


status_t
BlockAllocator::Free(Transaction& transaction, block_run run)
{
	MutexLocker lock(fLock);

	int32 group = run.AllocationGroup();
	uint16 start = run.Start();
	uint16 length = run.Length();

	FUNCTION_START(("group = %ld, start = %u, length = %u\n", group, start,
		length));
	T(Free(run));

	// doesn't use Volume::IsValidBlockRun() here because it can check better
	// against the group size (the last group may have a different length)
	if (group < 0 || group >= fNumGroups
		|| start > fGroups[group].NumBits()
		|| uint32(start + length) > fGroups[group].NumBits()
		|| length == 0) {
		FATAL(("tried to free an invalid block_run (%d, %u, %u)\n", (int)group,
			start, length));
		DEBUGGER(("tried to free invalid block_run"));
		return B_BAD_VALUE;
	}
	// check if someone tries to free reserved areas at the beginning of the
	// drive
	if (group == 0
		&& start < uint32(fVolume->Log().Start() + fVolume->Log().Length())) {
		FATAL(("tried to free a reserved block_run (%d, %u, %u)\n", (int)group,
			start, length));
		DEBUGGER(("tried to free reserved block"));
		return B_BAD_VALUE;
	}
#ifdef DEBUG
	if (CheckBlockRun(run) != B_OK)
		return B_BAD_DATA;
#endif

	CHECK_ALLOCATION_GROUP(group);

	if (fGroups[group].Free(transaction, start, length) != B_OK)
		RETURN_ERROR(B_IO_ERROR);

	CHECK_ALLOCATION_GROUP(group);

#ifdef DEBUG
	if (CheckBlockRun(run, NULL, NULL, false) != B_OK) {
		DEBUGGER(("CheckBlockRun() reports allocated blocks (which were just "
			"freed)\n"));
	}
#endif

	fVolume->SuperBlock().used_blocks =
		HOST_ENDIAN_TO_BFS_INT64(fVolume->UsedBlocks() - run.Length());
	return B_OK;
}


size_t
BlockAllocator::BitmapSize() const
{
	return fVolume->BlockSize() * fNumBlocks;
}


#ifdef DEBUG_FRAGMENTER
void
BlockAllocator::Fragment()
{
	AllocationBlock cached(fVolume);
	MutexLocker lock(fLock);

	// only leave 4 block holes
	static const uint32 kMask = 0x0f0f0f0f;
	uint32 valuesPerBlock = fVolume->BlockSize() / 4;

	for (int32 i = 0; i < fNumGroups; i++) {
		AllocationGroup& group = fGroups[i];

		for (uint32 block = 0; block < group.NumBlocks(); block++) {
			Transaction transaction(fVolume, 0);

			if (cached.SetToWritable(transaction, group, block) != B_OK)
				return;

			for (int32 index = 0; index < valuesPerBlock; index++) {
				cached.Block(index) |= HOST_ENDIAN_TO_BFS_INT32(kMask);
			}

			transaction.Done();
		}
	}
}
#endif	// DEBUG_FRAGMENTER


#ifdef DEBUG_ALLOCATION_GROUPS
void
BlockAllocator::_CheckGroup(int32 groupIndex) const
{
	AllocationBlock cached(fVolume);
	ASSERT_LOCKED_MUTEX(&fLock);

	AllocationGroup& group = fGroups[groupIndex];

	int32 currentStart = 0, currentLength = 0;
	int32 firstFree = -1;
	int32 largestStart = -1;
	int32 largestLength = 0;
	int32 currentBit = 0;

	for (uint32 block = 0; block < group.NumBlocks(); block++) {
		if (cached.SetTo(group, block) < B_OK) {
			panic("setting group block %d failed\n", (int)block);
			return;
		}

		for (uint32 bit = 0; bit < cached.NumBlockBits(); bit++) {
			if (!cached.IsUsed(bit)) {
				if (firstFree < 0) {
					firstFree = currentBit;
					if (!group.fLargestValid) {
						if (firstFree >= 0 && firstFree < group.fFirstFree) {
							// mostly harmless but noteworthy
							dprintf("group %d first free too late: should be "
								"%d, is %d\n", (int)groupIndex, (int)firstFree,
								(int)group.fFirstFree);
						}
						return;
					}
				}

				if (currentLength == 0) {
					// start new range
					currentStart = currentBit;
				}
				currentLength++;
			} else if (currentLength) {
				// end of a range
				if (currentLength > largestLength) {
					largestStart = currentStart;
					largestLength = currentLength;
				}
				currentLength = 0;
			}
			currentBit++;
		}
	}

	if (currentLength > largestLength) {
		largestStart = currentStart;
		largestLength = currentLength;
	}

	if (firstFree >= 0 && firstFree < group.fFirstFree) {
		// mostly harmless but noteworthy
		dprintf("group %d first free too late: should be %d, is %d\n",
			(int)groupIndex, (int)firstFree, (int)group.fFirstFree);
	}
	if (group.fLargestValid
		&& (largestStart != group.fLargestStart
			|| largestLength != group.fLargestLength)) {
		panic("bfs %p: group %d largest differs: %d.%d, checked %d.%d.\n",
			fVolume, (int)groupIndex, (int)group.fLargestStart,
			(int)group.fLargestLength, (int)largestStart, (int)largestLength);
	}
}
#endif	// DEBUG_ALLOCATION_GROUPS


//	#pragma mark - Bitmap validity checking

// TODO: implement new FS checking API
// Functions to check the validity of the bitmap - they are used from
// the "checkfs" command (since this does even a bit more, maybe we should
// move this some place else?)


bool
BlockAllocator::_IsValidCheckControl(check_control* control)
{
	if (control == NULL
		|| control->magic != BFS_IOCTL_CHECK_MAGIC) {
		FATAL(("invalid check_control (%p)!\n", control));
		return false;
	}

	return true;
}


status_t
BlockAllocator::StartChecking(check_control* control)
{
	if (!_IsValidCheckControl(control))
		return B_BAD_VALUE;

	fVolume->GetJournal(0)->Lock(NULL, true);
		// Lock the volume's journal

	status_t status = mutex_lock(&fLock);
	if (status != B_OK) {
		fVolume->GetJournal(0)->Unlock(NULL, true);
		return status;
	}

	size_t size = BitmapSize();
	fCheckBitmap = (uint32*)malloc(size);
	if (fCheckBitmap == NULL) {
		mutex_unlock(&fLock);
		fVolume->GetJournal(0)->Unlock(NULL, true);
		return B_NO_MEMORY;
	}

	check_cookie* cookie = new check_cookie();
	if (cookie == NULL) {
		free(fCheckBitmap);
		fCheckBitmap = NULL;
		mutex_unlock(&fLock);
		fVolume->GetJournal(0)->Unlock(NULL, true);

		return B_NO_MEMORY;
	}

	// initialize bitmap
	memset(fCheckBitmap, 0, size);
	for (int32 block = fVolume->Log().Start() + fVolume->Log().Length();
			block-- > 0;) {
		_SetCheckBitmapAt(block);
	}

	cookie->stack.Push(fVolume->Root());
	cookie->stack.Push(fVolume->Indices());
	cookie->iterator = NULL;
	control->cookie = cookie;

	fCheckCookie = cookie;
		// to be able to restore nicely if "chkbfs" exited abnormally

	// Put removed vnodes to the stack -- they are not reachable by traversing
	// the file system anymore.
	InodeList::Iterator iterator = fVolume->RemovedInodes().GetIterator();
	while (Inode* inode = iterator.Next()) {
		cookie->stack.Push(inode->BlockRun());
	}

	// TODO: check reserved area in bitmap!

	return B_OK;
}


status_t
BlockAllocator::StopChecking(check_control* control)
{
	check_cookie* cookie;
	if (control == NULL)
		cookie = fCheckCookie;
	else
		cookie = (check_cookie*)control->cookie;

	if (cookie == NULL)
		return B_ERROR;

	if (cookie->iterator != NULL) {
		delete cookie->iterator;
		cookie->iterator = NULL;

		// the current directory inode is still locked in memory
		put_vnode(fVolume->FSVolume(), fVolume->ToVnode(cookie->current));
	}

	if (fVolume->IsReadOnly()) {
		// We can't fix errors on this volume
		control->flags &= ~BFS_FIX_BITMAP_ERRORS;
	}

	// if CheckNextNode() could completely work through, we can
	// fix any damages of the bitmap
	if (control != NULL && control->status == B_ENTRY_NOT_FOUND) {
		// calculate the number of used blocks in the check bitmap
		size_t size = BitmapSize();
		off_t usedBlocks = 0LL;

		// TODO: update the allocation groups used blocks info
		for (uint32 i = size >> 2; i-- > 0;) {
			uint32 compare = 1;
			// Count the number of bits set
			for (int16 j = 0; j < 32; j++, compare <<= 1) {
				if ((compare & fCheckBitmap[i]) != 0)
					usedBlocks++;
			}
		}

		control->stats.freed = fVolume->UsedBlocks() - usedBlocks
			+ control->stats.missing;
		if (control->stats.freed < 0)
			control->stats.freed = 0;

		// Should we fix errors? Were there any errors we can fix?
		if ((control->flags & BFS_FIX_BITMAP_ERRORS) != 0
			&& (control->stats.freed != 0 || control->stats.missing != 0)) {
			// If so, write the check bitmap back over the original one,
			// and use transactions here to play safe - we even use several
			// transactions, so that we don't blow the maximum log size
			// on large disks, since we don't need to make this atomic.
#if 0
			// prints the blocks that differ
			off_t block = 0;
			for (int32 i = 0; i < fNumGroups; i++) {
				AllocationBlock cached(fVolume);
				for (uint32 j = 0; j < fGroups[i].NumBlocks(); j++) {
					cached.SetTo(fGroups[i], j);
					for (uint32 k = 0; k < cached.NumBlockBits(); k++) {
						if (cached.IsUsed(k) != _CheckBitmapIsUsedAt(block)) {
							dprintf("differ block %lld (should be %d)\n", block,
								_CheckBitmapIsUsedAt(block));
						}
						block++;
					}
				}
			}
#endif

			fVolume->SuperBlock().used_blocks
				= HOST_ENDIAN_TO_BFS_INT64(usedBlocks);

			int32 blocksInBitmap = fNumGroups * fBlocksPerGroup;
			size_t blockSize = fVolume->BlockSize();

			for (int32 i = 0; i < blocksInBitmap; i += 512) {
				Transaction transaction(fVolume, 1 + i);

				int32 blocksToWrite = 512;
				if (blocksToWrite + i > blocksInBitmap)
					blocksToWrite = blocksInBitmap - i;

				status_t status = transaction.WriteBlocks(1 + i,
					(uint8*)fCheckBitmap + i * blockSize, blocksToWrite);
				if (status < B_OK) {
					FATAL(("error writing bitmap: %s\n", strerror(status)));
					break;
				}
				transaction.Done();
			}
		}
	} else
		FATAL(("BlockAllocator::CheckNextNode() didn't run through\n"));

	fVolume->SetCheckingThread(-1);

	free(fCheckBitmap);
	fCheckBitmap = NULL;
	fCheckCookie = NULL;
	delete cookie;
	mutex_unlock(&fLock);
	fVolume->GetJournal(0)->Unlock(NULL, true);

	return B_OK;
}


status_t
BlockAllocator::CheckNextNode(check_control* control)
{
	if (!_IsValidCheckControl(control))
		return B_BAD_VALUE;

	check_cookie* cookie = (check_cookie*)control->cookie;
	fVolume->SetCheckingThread(find_thread(NULL));

	while (true) {
		if (cookie->iterator == NULL) {
			if (!cookie->stack.Pop(&cookie->current)) {
				// no more runs on the stack, we are obviously finished!
				control->status = B_ENTRY_NOT_FOUND;
				return B_ENTRY_NOT_FOUND;
			}

			Vnode vnode(fVolume, cookie->current);
			Inode* inode;
			if (vnode.Get(&inode) != B_OK) {
				FATAL(("check: Could not open inode at %" B_PRIdOFF "\n",
					fVolume->ToBlock(cookie->current)));
				continue;
			}

			control->inode = inode->ID();
			control->mode = inode->Mode();

			if (!inode->IsContainer()) {
				// Check file
				control->errors = 0;
				control->status = CheckInode(inode, control);

				if (inode->GetName(control->name) < B_OK)
					strcpy(control->name, "(node has no name)");

				return B_OK;
			}

			// get iterator for the next directory

			BPlusTree* tree = inode->Tree();
			if (tree == NULL) {
				FATAL(("check: could not open b+tree from inode at %" B_PRIdOFF
					"\n", fVolume->ToBlock(cookie->current)));
				continue;
			}

			cookie->parent = inode;
			cookie->parent_mode = inode->Mode();

			cookie->iterator = new TreeIterator(tree);
			if (cookie->iterator == NULL)
				RETURN_ERROR(B_NO_MEMORY);

			// the inode must stay locked in memory until the iterator is freed
			vnode.Keep();

			// check the inode of the directory
			control->errors = 0;
			control->status = CheckInode(inode, control);

			if (inode->GetName(control->name) < B_OK)
				strcpy(control->name, "(dir has no name)");

			return B_OK;
		}

		char name[B_FILE_NAME_LENGTH];
		uint16 length;
		ino_t id;

		status_t status = cookie->iterator->GetNextEntry(name, &length,
			B_FILE_NAME_LENGTH, &id);
		if (status == B_ENTRY_NOT_FOUND) {
			// there are no more entries in this iterator, free it and go on
			delete cookie->iterator;
			cookie->iterator = NULL;

			// unlock the directory's inode from memory
			put_vnode(fVolume->FSVolume(), fVolume->ToVnode(cookie->current));

			continue;
		} else if (status == B_OK) {
			// ignore "." and ".." entries
			if (!strcmp(name, ".") || !strcmp(name, ".."))
				continue;

			// fill in the control data as soon as we have them
			strlcpy(control->name, name, B_FILE_NAME_LENGTH);
			control->inode = id;
			control->errors = 0;

			Vnode vnode(fVolume, id);
			Inode* inode;
			if (vnode.Get(&inode) != B_OK) {
				FATAL(("Could not open inode ID %" B_PRIdINO "!\n", id));
				control->errors |= BFS_COULD_NOT_OPEN;

				if ((control->flags & BFS_REMOVE_INVALID) != 0) {
					status = _RemoveInvalidNode(cookie->parent,
						cookie->iterator->Tree(), NULL, name);
				} else
					status = B_ERROR;

				control->status = status;
				return B_OK;
			}

			// check if the inode's name is the same as in the b+tree
			if (inode->IsRegularNode()) {
				RecursiveLocker locker(inode->SmallDataLock());
				NodeGetter node(fVolume, inode);

				const char* localName = inode->Name(node.Node());
				if (localName == NULL || strcmp(localName, name)) {
					control->errors |= BFS_NAMES_DONT_MATCH;
					FATAL(("Names differ: tree \"%s\", inode \"%s\"\n", name,
						localName));

					if ((control->flags & BFS_FIX_NAME_MISMATCHES) != 0) {
						// Rename the inode
						Transaction transaction(fVolume, inode->BlockNumber());

						status = inode->SetName(transaction, name);
						if (status == B_OK)
							status = inode->WriteBack(transaction);
						if (status == B_OK)
							status = transaction.Done();
						if (status != B_OK) {
							control->status = status;
							return B_OK;
						}
					}
				}
			}

			control->mode = inode->Mode();

			// Check for the correct mode of the node (if the mode of the
			// file don't fit to its parent, there is a serious problem)
			if (((cookie->parent_mode & S_ATTR_DIR) != 0
					&& !inode->IsAttribute())
				|| ((cookie->parent_mode & S_INDEX_DIR) != 0
					&& !inode->IsIndex())
				|| (is_directory(cookie->parent_mode)
					&& !inode->IsRegularNode())) {
				FATAL(("inode at %" B_PRIdOFF " is of wrong type: %o (parent "
					"%o at %" B_PRIdOFF ")!\n", inode->BlockNumber(),
					inode->Mode(), cookie->parent_mode,
					cookie->parent->BlockNumber()));

				// if we are allowed to fix errors, we should remove the file
				if ((control->flags & BFS_REMOVE_WRONG_TYPES) != 0
					&& (control->flags & BFS_FIX_BITMAP_ERRORS) != 0) {
					status = _RemoveInvalidNode(cookie->parent, NULL, inode,
						name);
				} else
					status = B_ERROR;

				control->errors |= BFS_WRONG_TYPE;
				control->status = status;
				return B_OK;
			}

			// push the directory on the stack so that it will be scanned later
			if (inode->IsContainer() && !inode->IsIndex())
				cookie->stack.Push(inode->BlockRun());
			else {
				// check it now
				control->status = CheckInode(inode, control);

				return B_OK;
			}
		}
	}
	// is never reached
}


status_t
BlockAllocator::_RemoveInvalidNode(Inode* parent, BPlusTree* tree, Inode* inode,
	const char* name)
{
	// it's safe to start a transaction, because Inode::Remove()
	// won't touch the block bitmap (which we hold the lock for)
	// if we set the INODE_DONT_FREE_SPACE flag - since we fix
	// the bitmap anyway
	Transaction transaction(fVolume, parent->BlockNumber());
	status_t status;

	if (inode != NULL) {
		inode->Node().flags |= HOST_ENDIAN_TO_BFS_INT32(INODE_DONT_FREE_SPACE);

		status = parent->Remove(transaction, name, NULL, false, true);
	} else {
		parent->WriteLockInTransaction(transaction);

		// does the file even exist?
		off_t id;
		status = tree->Find((uint8*)name, (uint16)strlen(name), &id);
		if (status == B_OK)
			status = tree->Remove(transaction, name, id);
	}

	if (status == B_OK)
		transaction.Done();

	return status;
}


bool
BlockAllocator::_CheckBitmapIsUsedAt(off_t block) const
{
	size_t size = BitmapSize();
	uint32 index = block / 32;	// 32bit resolution
	if (index > size / 4)
		return false;

	return BFS_ENDIAN_TO_HOST_INT32(fCheckBitmap[index])
		& (1UL << (block & 0x1f));
}


void
BlockAllocator::_SetCheckBitmapAt(off_t block)
{
	size_t size = BitmapSize();
	uint32 index = block / 32;	// 32bit resolution
	if (index > size / 4)
		return;

	fCheckBitmap[index] |= HOST_ENDIAN_TO_BFS_INT32(1UL << (block & 0x1f));
}


/*!	Checks whether or not the specified block range is allocated or not,
	depending on the \a allocated argument.
*/
status_t
BlockAllocator::CheckBlocks(off_t start, off_t length, bool allocated)
{
	if (start < 0 || start + length > fVolume->NumBlocks())
		return B_BAD_VALUE;

	uint32 group = start >> fVolume->AllocationGroupShift();
	uint32 groupBlock = start / (fVolume->BlockSize() << 3);
	uint32 blockOffset = start % fVolume->BlockSize();

	AllocationBlock cached(fVolume);

	while (groupBlock < fGroups[group].NumBlocks() && length > 0) {
		if (cached.SetTo(fGroups[group], groupBlock) != B_OK)
			RETURN_ERROR(B_IO_ERROR);

		for (; blockOffset < cached.NumBlockBits() && length > 0;
				blockOffset++, length--) {
			if (cached.IsUsed(blockOffset) != allocated) {
				RETURN_ERROR(B_BAD_DATA);
			}
		}

		blockOffset = 0;

		if (++groupBlock >= fGroups[group].NumBlocks()) {
			groupBlock = 0;
			group++;
		}
	}

	return B_OK;
}


status_t
BlockAllocator::CheckBlockRun(block_run run, const char* type,
	check_control* control, bool allocated)
{
	if (run.AllocationGroup() < 0 || run.AllocationGroup() >= fNumGroups
		|| run.Start() > fGroups[run.AllocationGroup()].fNumBits
		|| uint32(run.Start() + run.Length())
				> fGroups[run.AllocationGroup()].fNumBits
		|| run.length == 0) {
		PRINT(("%s: block_run(%ld, %u, %u) is invalid!\n", type,
			run.AllocationGroup(), run.Start(), run.Length()));
		if (control == NULL)
			return B_BAD_DATA;

		control->errors |= BFS_INVALID_BLOCK_RUN;
		return B_OK;
	}

	uint32 bitsPerBlock = fVolume->BlockSize() << 3;
	uint32 block = run.Start() / bitsPerBlock;
	uint32 pos = run.Start() % bitsPerBlock;
	int32 length = 0;
	off_t firstMissing = -1, firstSet = -1;
	off_t firstGroupBlock
		= (off_t)run.AllocationGroup() << fVolume->AllocationGroupShift();

	AllocationBlock cached(fVolume);

	for (; block < fBlocksPerGroup && length < run.Length(); block++, pos = 0) {
		if (cached.SetTo(fGroups[run.AllocationGroup()], block) < B_OK)
			RETURN_ERROR(B_IO_ERROR);

		if (pos >= cached.NumBlockBits()) {
			// something very strange has happened...
			RETURN_ERROR(B_ERROR);
		}

		while (length < run.Length() && pos < cached.NumBlockBits()) {
			if (cached.IsUsed(pos) != allocated) {
				if (control == NULL) {
					PRINT(("%s: block_run(%ld, %u, %u) is only partially "
						"allocated (pos = %ld, length = %ld)!\n", type,
						run.AllocationGroup(), run.Start(), run.Length(),
						pos, length));
					return B_BAD_DATA;
				}
				if (firstMissing == -1) {
					firstMissing = firstGroupBlock + pos + block * bitsPerBlock;
					control->errors |= BFS_MISSING_BLOCKS;
				}
				control->stats.missing++;
			} else if (firstMissing != -1) {
				PRINT(("%s: block_run(%ld, %u, %u): blocks %Ld - %Ld are "
					"%sallocated!\n", type, run.AllocationGroup(), run.Start(),
					run.Length(), firstMissing,
					firstGroupBlock + pos + block * bitsPerBlock - 1,
					allocated ? "not " : ""));
				firstMissing = -1;
			}

			if (fCheckBitmap != NULL) {
				// Set the block in the check bitmap as well, but have a look
				// if it is already allocated first
				uint32 offset = pos + block * bitsPerBlock;
				if (_CheckBitmapIsUsedAt(firstGroupBlock + offset)) {
					if (firstSet == -1) {
						firstSet = firstGroupBlock + offset;
						control->errors |= BFS_BLOCKS_ALREADY_SET;
						dprintf("block %" B_PRIdOFF " is already set!!!\n",
							firstGroupBlock + offset);
					}
					control->stats.already_set++;
				} else {
					if (firstSet != -1) {
						FATAL(("%s: block_run(%d, %u, %u): blocks %" B_PRIdOFF
							" - %" B_PRIdOFF " are already set!\n", type,
							(int)run.AllocationGroup(), run.Start(),
							run.Length(), firstSet,
							firstGroupBlock + offset - 1));
						firstSet = -1;
					}
					_SetCheckBitmapAt(firstGroupBlock + offset);
				}
			}
			length++;
			pos++;
		}

		if (block + 1 >= fBlocksPerGroup || length >= run.Length()) {
			if (firstMissing != -1) {
				PRINT(("%s: block_run(%ld, %u, %u): blocks %Ld - %Ld are not "
					"allocated!\n", type, run.AllocationGroup(), run.Start(),
					run.Length(), firstMissing,
					firstGroupBlock + pos + block * bitsPerBlock - 1));
			}
			if (firstSet != -1) {
				FATAL(("%s: block_run(%d, %u, %u): blocks %" B_PRIdOFF " - %"
					B_PRIdOFF " are already set!\n", type,
					(int)run.AllocationGroup(), run.Start(), run.Length(),
					firstSet,
					firstGroupBlock + pos + block * bitsPerBlock - 1));
			}
		}
	}

	return B_OK;
}


status_t
BlockAllocator::CheckInode(Inode* inode, check_control* control)
{
	if (control != NULL && fCheckBitmap == NULL)
		return B_NO_INIT;
	if (inode == NULL)
		return B_BAD_VALUE;

	status_t status = CheckBlockRun(inode->BlockRun(), "inode", control);
	if (status != B_OK)
		return status;

	// If the inode has an attribute directory, push it on the stack
	if (!inode->Attributes().IsZero()) {
		check_cookie* cookie = (check_cookie*)control->cookie;
		cookie->stack.Push(inode->Attributes());
	}

	if (inode->IsSymLink() && (inode->Flags() & INODE_LONG_SYMLINK) == 0) {
		// symlinks may not have a valid data stream
		if (strlen(inode->Node().short_symlink) >= SHORT_SYMLINK_NAME_LENGTH)
			return B_BAD_DATA;

		return B_OK;
	}

	data_stream* data = &inode->Node().data;

	// check the direct range

	if (data->max_direct_range) {
		for (int32 i = 0; i < NUM_DIRECT_BLOCKS; i++) {
			if (data->direct[i].IsZero())
				break;

			status = CheckBlockRun(data->direct[i], "direct", control);
			if (status < B_OK)
				return status;
		}
	}

	CachedBlock cached(fVolume);

	// check the indirect range

	if (data->max_indirect_range) {
		status = CheckBlockRun(data->indirect, "indirect", control);
		if (status < B_OK)
			return status;

		off_t block = fVolume->ToBlock(data->indirect);

		for (int32 i = 0; i < data->indirect.Length(); i++) {
			block_run* runs = (block_run*)cached.SetTo(block + i);
			if (runs == NULL)
				RETURN_ERROR(B_IO_ERROR);

			int32 runsPerBlock = fVolume->BlockSize() / sizeof(block_run);
			int32 index = 0;
			for (; index < runsPerBlock; index++) {
				if (runs[index].IsZero())
					break;

				status = CheckBlockRun(runs[index], "indirect->run", control);
				if (status < B_OK)
					return status;
			}
			if (index < runsPerBlock)
				break;
		}
	}

	// check the double indirect range

	if (data->max_double_indirect_range) {
		status = CheckBlockRun(data->double_indirect, "double indirect",
			control);
		if (status != B_OK)
			return status;

		int32 runsPerBlock = runs_per_block(fVolume->BlockSize());
		int32 runsPerArray = runsPerBlock * data->double_indirect.Length();

		CachedBlock cachedDirect(fVolume);

		for (int32 indirectIndex = 0; indirectIndex < runsPerArray;
				indirectIndex++) {
			// get the indirect array block
			block_run* array = (block_run*)cached.SetTo(
				fVolume->ToBlock(data->double_indirect)
					+ indirectIndex / runsPerBlock);
			if (array == NULL)
				return B_IO_ERROR;

			block_run indirect = array[indirectIndex % runsPerBlock];
			// are we finished yet?
			if (indirect.IsZero())
				return B_OK;

			status = CheckBlockRun(indirect, "double indirect->runs", control);
			if (status != B_OK)
				return status;

			int32 maxIndex = (indirect.Length() << fVolume->BlockShift())
				/ sizeof(block_run);

			for (int32 index = 0; index < maxIndex; ) {
				block_run* runs = (block_run*)cachedDirect.SetTo(
					fVolume->ToBlock(indirect) + index / runsPerBlock);
				if (runs == NULL)
					return B_IO_ERROR;

				do {
					// are we finished yet?
					if (runs[index % runsPerBlock].IsZero())
						return B_OK;

					status = CheckBlockRun(runs[index % runsPerBlock],
						"double indirect->runs->run", control);
					if (status != B_OK)
						return status;
				} while ((++index % runsPerArray) != 0);
			}
		}
	}

	return B_OK;
}


//	#pragma mark - debugger commands


#ifdef BFS_DEBUGGER_COMMANDS

void
BlockAllocator::Dump(int32 index)
{
	kprintf("allocation groups: %ld (base %p)\n", fNumGroups, fGroups);
	kprintf("blocks per group: %ld\n", fBlocksPerGroup);

	for (int32 i = 0; i < fNumGroups; i++) {
		if (index != -1 && i != index)
			continue;

		AllocationGroup& group = fGroups[i];

		kprintf("[%3ld] num bits:       %lu  (%p)\n", i, group.NumBits(),
			&group);
		kprintf("      num blocks:     %lu\n", group.NumBlocks());
		kprintf("      start:          %ld\n", group.Start());
		kprintf("      first free:     %ld\n", group.fFirstFree);
		kprintf("      largest start:  %ld%s\n", group.fLargestStart,
			group.fLargestValid ? "" : "  (invalid)");
		kprintf("      largest length: %ld\n", group.fLargestLength);
		kprintf("      free bits:      %ld\n", group.fFreeBits);
	}
}


#if BFS_TRACING
static char kTraceBuffer[256];


int
dump_block_allocator_blocks(int argc, char** argv)
{
	if (argc != 3 || !strcmp(argv[1], "--help")) {
		kprintf("usage: %s <ptr-to-volume> <block>\n", argv[0]);
		return 0;
	}

	Volume* volume = (Volume*)parse_expression(argv[1]);
	off_t block = parse_expression(argv[2]);

	// iterate over all tracing entries to find overlapping actions

	using namespace BFSBlockTracing;

	LazyTraceOutput out(kTraceBuffer, sizeof(kTraceBuffer), 0);
	TraceEntryIterator iterator;
	while (TraceEntry* _entry = iterator.Next()) {
		if (Allocate* entry = dynamic_cast<Allocate*>(_entry)) {
			off_t first = volume->ToBlock(entry->Run());
			off_t last = first - 1 + entry->Run().Length();
			if (block >= first && block <= last) {
				out.Clear();
				const char* dump = out.DumpEntry(entry);
				kprintf("%5ld. %s\n", iterator.Index(), dump);
			}
		} else if (Free* entry = dynamic_cast<Free*>(_entry)) {
			off_t first = volume->ToBlock(entry->Run());
			off_t last = first - 1 + entry->Run().Length();
			if (block >= first && block <= last) {
				out.Clear();
				const char* dump = out.DumpEntry(entry);
				kprintf("%5ld. %s\n", iterator.Index(), dump);
			}
		}
	}

	return 0;
}
#endif


int
dump_block_allocator(int argc, char** argv)
{
	int32 group = -1;
	if (argc == 3) {
		group = parse_expression(argv[2]);
		argc--;
	}

	if (argc != 2 || !strcmp(argv[1], "--help")) {
		kprintf("usage: %s <ptr-to-volume> [group]\n", argv[0]);
		return 0;
	}

	Volume* volume = (Volume*)parse_expression(argv[1]);
	BlockAllocator& allocator = volume->Allocator();

	allocator.Dump(group);
	return 0;
}

#endif	// BFS_DEBUGGER_COMMANDS