exfat/cluster.c - android_bootable_recovery - Gitiles

 /*
 	cluster.c (03.09.09)
 	exFAT file system implementation library.

 	Copyright (C) 2010-2012  Andrew Nayenko

 	This program is free software: you can redistribute it and/or modify
 	it under the terms of the GNU General Public License as published by
 	the Free Software Foundation, either version 3 of the License, or
 	(at your option) any later version.

 	This program is distributed in the hope that it will be useful,
 	but WITHOUT ANY WARRANTY; without even the implied warranty of
 	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 	GNU General Public License for more details.

 	You should have received a copy of the GNU General Public License
 	along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

 #include "exfat.h"
 #include <errno.h>
 #include <string.h>

 /*
  * Sector to absolute offset.
  */
 static off64_t s2o(const struct exfat* ef, off64_t sector)
 {
 	return sector << ef->sb->sector_bits;
 }

 /*
  * Cluster to sector.
  */
 static off64_t c2s(const struct exfat* ef, cluster_t cluster)
 {
 	if (cluster < EXFAT_FIRST_DATA_CLUSTER)
 		exfat_bug("invalid cluster number %u", cluster);
 	return le32_to_cpu(ef->sb->cluster_sector_start) +
 		((off64_t) (cluster - EXFAT_FIRST_DATA_CLUSTER) << ef->sb->spc_bits);
 }

 /*
  * Cluster to absolute offset.
  */
 off64_t exfat_c2o(const struct exfat* ef, cluster_t cluster)
 {
 	return s2o(ef, c2s(ef, cluster));
 }

 /*
  * Sector to cluster.
  */
 static cluster_t s2c(const struct exfat* ef, off64_t sector)
 {
 	return ((sector - le32_to_cpu(ef->sb->cluster_sector_start)) >>
 			ef->sb->spc_bits) + EXFAT_FIRST_DATA_CLUSTER;
 }

 /*
  * Size in bytes to size in clusters (rounded upwards).
  */
 static uint32_t bytes2clusters(const struct exfat* ef, uint64_t bytes)
 {
 	uint64_t cluster_size = CLUSTER_SIZE(*ef->sb);
 	return (bytes + cluster_size - 1) / cluster_size;
 }

 cluster_t exfat_next_cluster(const struct exfat* ef,
 		const struct exfat_node* node, cluster_t cluster)
 {
 	le32_t next;
 	off64_t fat_offset;

 	if (cluster < EXFAT_FIRST_DATA_CLUSTER)
 		exfat_bug("bad cluster 0x%x", cluster);

 	if (IS_CONTIGUOUS(*node))
 		return cluster + 1;
 	fat_offset = s2o(ef, le32_to_cpu(ef->sb->fat_sector_start))
 		+ cluster * sizeof(cluster_t);
 	exfat_pread(ef->dev, &next, sizeof(next), fat_offset);
 	return le32_to_cpu(next);
 }

 cluster_t exfat_advance_cluster(const struct exfat* ef,
 		struct exfat_node* node, uint32_t count)
 {
 	uint32_t i;

 	if (node->fptr_index > count)
 	{
 		node->fptr_index = 0;
 		node->fptr_cluster = node->start_cluster;
 	}

 	for (i = node->fptr_index; i < count; i++)
 	{
 		node->fptr_cluster = exfat_next_cluster(ef, node, node->fptr_cluster);
 		if (CLUSTER_INVALID(node->fptr_cluster))
 			break; /* the caller should handle this and print appropriate
 			          error message */
 	}
 	node->fptr_index = count;
 	return node->fptr_cluster;
 }

 static cluster_t find_bit_and_set(uint8_t* bitmap, size_t start, size_t end)
 {
 	const size_t start_index = start / 8;
 	const size_t end_index = DIV_ROUND_UP(end, 8);
 	size_t i;
 	size_t c;

 	for (i = start_index; i < end_index; i++)
 	{
 		if (bitmap[i] == 0xff)
 			continue;
 		for (c = MAX(i * 8, start); c < MIN((i + 1) * 8, end); c++)
 			if (BMAP_GET(bitmap, c) == 0)
 			{
 				BMAP_SET(bitmap, c);
 				return c + EXFAT_FIRST_DATA_CLUSTER;
 			}
 	}
 	return EXFAT_CLUSTER_END;
 }

 void exfat_flush_cmap(struct exfat* ef)
 {
 	exfat_pwrite(ef->dev, ef->cmap.chunk, (ef->cmap.chunk_size + 7) / 8,
 			exfat_c2o(ef, ef->cmap.start_cluster));
 	ef->cmap.dirty = false;
 }

 static void set_next_cluster(const struct exfat* ef, int contiguous,
 		cluster_t current, cluster_t next)
 {
 	off64_t fat_offset;
 	le32_t next_le32;

 	if (contiguous)
 		return;
 	fat_offset = s2o(ef, le32_to_cpu(ef->sb->fat_sector_start))
 		+ current * sizeof(cluster_t);
 	next_le32 = cpu_to_le32(next);
 	exfat_pwrite(ef->dev, &next_le32, sizeof(next_le32), fat_offset);
 }

 static cluster_t allocate_cluster(struct exfat* ef, cluster_t hint)
 {
 	cluster_t cluster;

 	hint -= EXFAT_FIRST_DATA_CLUSTER;
 	if (hint >= ef->cmap.chunk_size)
 		hint = 0;

 	cluster = find_bit_and_set(ef->cmap.chunk, hint, ef->cmap.chunk_size);
 	if (cluster == EXFAT_CLUSTER_END)
 		cluster = find_bit_and_set(ef->cmap.chunk, 0, hint);
 	if (cluster == EXFAT_CLUSTER_END)
 	{
 		exfat_error("no free space left");
 		return EXFAT_CLUSTER_END;
 	}

 	ef->cmap.dirty = true;
 	return cluster;
 }

 static void free_cluster(struct exfat* ef, cluster_t cluster)
 {
 	if (CLUSTER_INVALID(cluster))
 		exfat_bug("freeing invalid cluster 0x%x", cluster);
 	if (cluster - EXFAT_FIRST_DATA_CLUSTER >= ef->cmap.size)
 		exfat_bug("freeing non-existing cluster 0x%x (0x%x)", cluster,
 				ef->cmap.size);

 	BMAP_CLR(ef->cmap.chunk, cluster - EXFAT_FIRST_DATA_CLUSTER);
 	ef->cmap.dirty = true;
 }

 static void make_noncontiguous(const struct exfat* ef, cluster_t first,
 		cluster_t last)
 {
 	cluster_t c;

 	for (c = first; c < last; c++)
 		set_next_cluster(ef, 0, c, c + 1);
 }

 static int shrink_file(struct exfat* ef, struct exfat_node* node,
 		uint32_t current, uint32_t difference);

 static int grow_file(struct exfat* ef, struct exfat_node* node,
 		uint32_t current, uint32_t difference)
 {
 	cluster_t previous;
 	cluster_t next;
 	uint32_t allocated = 0;

 	if (difference == 0)
 		exfat_bug("zero clusters count passed");

 	if (node->start_cluster != EXFAT_CLUSTER_FREE)
 	{
 		/* get the last cluster of the file */
 		previous = exfat_advance_cluster(ef, node, current - 1);
 		if (CLUSTER_INVALID(previous))
 		{
 			exfat_error("invalid cluster 0x%x while growing", previous);
 			return -EIO;
 		}
 	}
 	else
 	{
 		if (node->fptr_index != 0)
 			exfat_bug("non-zero pointer index (%u)", node->fptr_index);
 		/* file does not have clusters (i.e. is empty), allocate
 		   the first one for it */
 		previous = allocate_cluster(ef, 0);
 		if (CLUSTER_INVALID(previous))
 			return -ENOSPC;
 		node->fptr_cluster = node->start_cluster = previous;
 		allocated = 1;
 		/* file consists of only one cluster, so it's contiguous */
 		node->flags |= EXFAT_ATTRIB_CONTIGUOUS;
 	}

 	while (allocated < difference)
 	{
 		next = allocate_cluster(ef, previous + 1);
 		if (CLUSTER_INVALID(next))
 		{
 			if (allocated != 0)
 				shrink_file(ef, node, current + allocated, allocated);
 			return -ENOSPC;
 		}
 		if (next != previous - 1 && IS_CONTIGUOUS(*node))
 		{
 			/* it's a pity, but we are not able to keep the file contiguous
 			   anymore */
 			make_noncontiguous(ef, node->start_cluster, previous);
 			node->flags &= ~EXFAT_ATTRIB_CONTIGUOUS;
 			node->flags |= EXFAT_ATTRIB_DIRTY;
 		}
 		set_next_cluster(ef, IS_CONTIGUOUS(*node), previous, next);
 		previous = next;
 		allocated++;
 	}

 	set_next_cluster(ef, IS_CONTIGUOUS(*node), previous, EXFAT_CLUSTER_END);
 	return 0;
 }

 static int shrink_file(struct exfat* ef, struct exfat_node* node,
 		uint32_t current, uint32_t difference)
 {
 	cluster_t previous;
 	cluster_t next;

 	if (difference == 0)
 		exfat_bug("zero difference passed");
 	if (node->start_cluster == EXFAT_CLUSTER_FREE)
 		exfat_bug("unable to shrink empty file (%u clusters)", current);
 	if (current < difference)
 		exfat_bug("file underflow (%u < %u)", current, difference);

 	/* crop the file */
 	if (current > difference)
 	{
 		cluster_t last = exfat_advance_cluster(ef, node,
 				current - difference - 1);
 		if (CLUSTER_INVALID(last))
 		{
 			exfat_error("invalid cluster 0x%x while shrinking", last);
 			return -EIO;
 		}
 		previous = exfat_next_cluster(ef, node, last);
 		set_next_cluster(ef, IS_CONTIGUOUS(*node), last, EXFAT_CLUSTER_END);
 	}
 	else
 	{
 		previous = node->start_cluster;
 		node->start_cluster = EXFAT_CLUSTER_FREE;
 	}
 	node->fptr_index = 0;
 	node->fptr_cluster = node->start_cluster;

 	/* free remaining clusters */
 	while (difference--)
 	{
 		if (CLUSTER_INVALID(previous))
 		{
 			exfat_error("invalid cluster 0x%x while freeing after shrink",
 					previous);
 			return -EIO;
 		}
 		next = exfat_next_cluster(ef, node, previous);
 		set_next_cluster(ef, IS_CONTIGUOUS(*node), previous,
 				EXFAT_CLUSTER_FREE);
 		free_cluster(ef, previous);
 		previous = next;
 	}
 	return 0;
 }

 static void erase_raw(struct exfat* ef, size_t size, off64_t offset)
 {
 	exfat_pwrite(ef->dev, ef->zero_cluster, size, offset);
 }

 static int erase_range(struct exfat* ef, struct exfat_node* node,
 		uint64_t begin, uint64_t end)
 {
 	uint64_t cluster_boundary;
 	cluster_t cluster;

 	if (begin >= end)
 		return 0;

 	cluster_boundary = (begin | (CLUSTER_SIZE(*ef->sb) - 1)) + 1;
 	cluster = exfat_advance_cluster(ef, node,
 			begin / CLUSTER_SIZE(*ef->sb));
 	if (CLUSTER_INVALID(cluster))
 	{
 		exfat_error("invalid cluster 0x%x while erasing", cluster);
 		return -EIO;
 	}
 	/* erase from the beginning to the closest cluster boundary */
 	erase_raw(ef, MIN(cluster_boundary, end) - begin,
 			exfat_c2o(ef, cluster) + begin % CLUSTER_SIZE(*ef->sb));
 	/* erase whole clusters */
 	while (cluster_boundary < end)
 	{
 		cluster = exfat_next_cluster(ef, node, cluster);
 		/* the cluster cannot be invalid because we have just allocated it */
 		if (CLUSTER_INVALID(cluster))
 			exfat_bug("invalid cluster 0x%x after allocation", cluster);
 		erase_raw(ef, CLUSTER_SIZE(*ef->sb), exfat_c2o(ef, cluster));
 		cluster_boundary += CLUSTER_SIZE(*ef->sb);
 	}
 	return 0;
 }

 int exfat_truncate(struct exfat* ef, struct exfat_node* node, uint64_t size)
 {
 	uint32_t c1 = bytes2clusters(ef, node->size);
 	uint32_t c2 = bytes2clusters(ef, size);
 	int rc = 0;

 	if (node->references == 0 && node->parent)
 		exfat_bug("no references, node changes can be lost");

 	if (node->size == size)
 		return 0;

 	if (c1 < c2)
 		rc = grow_file(ef, node, c1, c2 - c1);
 	else if (c1 > c2)
 		rc = shrink_file(ef, node, c1, c1 - c2);

 	if (rc != 0)
 		return rc;

 	rc = erase_range(ef, node, node->size, size);
 	if (rc != 0)
 		return rc;

 	exfat_update_mtime(node);
 	node->size = size;
 	node->flags |= EXFAT_ATTRIB_DIRTY;
 	return 0;
 }

 uint32_t exfat_count_free_clusters(const struct exfat* ef)
 {
 	uint32_t free_clusters = 0;
 	uint32_t i;

 	for (i = 0; i < ef->cmap.size; i++)
 		if (BMAP_GET(ef->cmap.chunk, i) == 0)
 			free_clusters++;
 	return free_clusters;
 }

 static int find_used_clusters(const struct exfat* ef,
 		cluster_t* a, cluster_t* b)
 {
 	const cluster_t end = le32_to_cpu(ef->sb->cluster_count);

 	/* find first used cluster */
 	for (*a = *b + 1; *a < end; (*a)++)
 		if (BMAP_GET(ef->cmap.chunk, *a - EXFAT_FIRST_DATA_CLUSTER))
 			break;
 	if (*a >= end)
 		return 1;

 	/* find last contiguous used cluster */
 	for (*b = *a; *b < end; (*b)++)
 		if (BMAP_GET(ef->cmap.chunk, *b - EXFAT_FIRST_DATA_CLUSTER) == 0)
 		{
 			(*b)--;
 			break;
 		}

 	return 0;
 }

 int exfat_find_used_sectors(const struct exfat* ef, off64_t* a, off64_t* b)
 {
 	cluster_t ca, cb;

 	if (*a == 0 && *b == 0)
 		ca = cb = EXFAT_FIRST_DATA_CLUSTER - 1;
 	else
 	{
 		ca = s2c(ef, *a);
 		cb = s2c(ef, *b);
 	}
 	if (find_used_clusters(ef, &ca, &cb) != 0)
 		return 1;
 	if (*a != 0 || *b != 0)
 		*a = c2s(ef, ca);
 	*b = c2s(ef, cb) + (CLUSTER_SIZE(*ef->sb) - 1) / SECTOR_SIZE(*ef->sb);
 	return 0;
 }
	/*
	cluster.c (03.09.09)
	exFAT file system implementation library.

	Copyright (C) 2010-2012 Andrew Nayenko

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program. If not, see <http://www.gnu.org/licenses/>.
	*/

	#include "exfat.h"
	#include <errno.h>
	#include <string.h>

	/*
	* Sector to absolute offset.
	*/
	static off64_t s2o(const struct exfat* ef, off64_t sector)
	{
	return sector << ef->sb->sector_bits;
	}

	/*
	* Cluster to sector.
	*/
	static off64_t c2s(const struct exfat* ef, cluster_t cluster)
	{
	if (cluster < EXFAT_FIRST_DATA_CLUSTER)
	exfat_bug("invalid cluster number %u", cluster);
	return le32_to_cpu(ef->sb->cluster_sector_start) +
	((off64_t) (cluster - EXFAT_FIRST_DATA_CLUSTER) << ef->sb->spc_bits);
	}

	/*
	* Cluster to absolute offset.
	*/
	off64_t exfat_c2o(const struct exfat* ef, cluster_t cluster)
	{
	return s2o(ef, c2s(ef, cluster));
	}

	/*
	* Sector to cluster.
	*/
	static cluster_t s2c(const struct exfat* ef, off64_t sector)
	{
	return ((sector - le32_to_cpu(ef->sb->cluster_sector_start)) >>
	ef->sb->spc_bits) + EXFAT_FIRST_DATA_CLUSTER;
	}

	/*
	* Size in bytes to size in clusters (rounded upwards).
	*/
	static uint32_t bytes2clusters(const struct exfat* ef, uint64_t bytes)
	{
	uint64_t cluster_size = CLUSTER_SIZE(*ef->sb);
	return (bytes + cluster_size - 1) / cluster_size;
	}

	cluster_t exfat_next_cluster(const struct exfat* ef,
	const struct exfat_node* node, cluster_t cluster)
	{
	le32_t next;
	off64_t fat_offset;

	if (cluster < EXFAT_FIRST_DATA_CLUSTER)
	exfat_bug("bad cluster 0x%x", cluster);

	if (IS_CONTIGUOUS(*node))
	return cluster + 1;
	fat_offset = s2o(ef, le32_to_cpu(ef->sb->fat_sector_start))
	+ cluster * sizeof(cluster_t);
	exfat_pread(ef->dev, &next, sizeof(next), fat_offset);
	return le32_to_cpu(next);
	}

	cluster_t exfat_advance_cluster(const struct exfat* ef,
	struct exfat_node* node, uint32_t count)
	{
	uint32_t i;

	if (node->fptr_index > count)
	{
	node->fptr_index = 0;
	node->fptr_cluster = node->start_cluster;
	}

	for (i = node->fptr_index; i < count; i++)
	{
	node->fptr_cluster = exfat_next_cluster(ef, node, node->fptr_cluster);
	if (CLUSTER_INVALID(node->fptr_cluster))
	break; /* the caller should handle this and print appropriate
	error message */
	}
	node->fptr_index = count;
	return node->fptr_cluster;
	}

	static cluster_t find_bit_and_set(uint8_t* bitmap, size_t start, size_t end)
	{
	const size_t start_index = start / 8;
	const size_t end_index = DIV_ROUND_UP(end, 8);
	size_t i;
	size_t c;

	for (i = start_index; i < end_index; i++)
	{
	if (bitmap[i] == 0xff)
	continue;
	for (c = MAX(i * 8, start); c < MIN((i + 1) * 8, end); c++)
	if (BMAP_GET(bitmap, c) == 0)
	{
	BMAP_SET(bitmap, c);
	return c + EXFAT_FIRST_DATA_CLUSTER;
	}
	}
	return EXFAT_CLUSTER_END;
	}

	void exfat_flush_cmap(struct exfat* ef)
	{
	exfat_pwrite(ef->dev, ef->cmap.chunk, (ef->cmap.chunk_size + 7) / 8,
	exfat_c2o(ef, ef->cmap.start_cluster));
	ef->cmap.dirty = false;
	}

	static void set_next_cluster(const struct exfat* ef, int contiguous,
	cluster_t current, cluster_t next)
	{
	off64_t fat_offset;
	le32_t next_le32;

	if (contiguous)
	return;
	fat_offset = s2o(ef, le32_to_cpu(ef->sb->fat_sector_start))
	+ current * sizeof(cluster_t);
	next_le32 = cpu_to_le32(next);
	exfat_pwrite(ef->dev, &next_le32, sizeof(next_le32), fat_offset);
	}

	static cluster_t allocate_cluster(struct exfat* ef, cluster_t hint)
	{
	cluster_t cluster;

	hint -= EXFAT_FIRST_DATA_CLUSTER;
	if (hint >= ef->cmap.chunk_size)
	hint = 0;

	cluster = find_bit_and_set(ef->cmap.chunk, hint, ef->cmap.chunk_size);
	if (cluster == EXFAT_CLUSTER_END)
	cluster = find_bit_and_set(ef->cmap.chunk, 0, hint);
	if (cluster == EXFAT_CLUSTER_END)
	{
	exfat_error("no free space left");
	return EXFAT_CLUSTER_END;
	}

	ef->cmap.dirty = true;
	return cluster;
	}

	static void free_cluster(struct exfat* ef, cluster_t cluster)
	{
	if (CLUSTER_INVALID(cluster))
	exfat_bug("freeing invalid cluster 0x%x", cluster);
	if (cluster - EXFAT_FIRST_DATA_CLUSTER >= ef->cmap.size)
	exfat_bug("freeing non-existing cluster 0x%x (0x%x)", cluster,
	ef->cmap.size);

	BMAP_CLR(ef->cmap.chunk, cluster - EXFAT_FIRST_DATA_CLUSTER);
	ef->cmap.dirty = true;
	}

	static void make_noncontiguous(const struct exfat* ef, cluster_t first,
	cluster_t last)
	{
	cluster_t c;

	for (c = first; c < last; c++)
	set_next_cluster(ef, 0, c, c + 1);
	}

	static int shrink_file(struct exfat* ef, struct exfat_node* node,
	uint32_t current, uint32_t difference);

	static int grow_file(struct exfat* ef, struct exfat_node* node,
	uint32_t current, uint32_t difference)
	{
	cluster_t previous;
	cluster_t next;
	uint32_t allocated = 0;

	if (difference == 0)
	exfat_bug("zero clusters count passed");

	if (node->start_cluster != EXFAT_CLUSTER_FREE)
	{
	/* get the last cluster of the file */
	previous = exfat_advance_cluster(ef, node, current - 1);
	if (CLUSTER_INVALID(previous))
	{
	exfat_error("invalid cluster 0x%x while growing", previous);
	return -EIO;
	}
	}
	else
	{
	if (node->fptr_index != 0)
	exfat_bug("non-zero pointer index (%u)", node->fptr_index);
	/* file does not have clusters (i.e. is empty), allocate
	the first one for it */
	previous = allocate_cluster(ef, 0);
	if (CLUSTER_INVALID(previous))
	return -ENOSPC;
	node->fptr_cluster = node->start_cluster = previous;
	allocated = 1;
	/* file consists of only one cluster, so it's contiguous */
	node->flags \|= EXFAT_ATTRIB_CONTIGUOUS;
	}

	while (allocated < difference)
	{
	next = allocate_cluster(ef, previous + 1);
	if (CLUSTER_INVALID(next))
	{
	if (allocated != 0)
	shrink_file(ef, node, current + allocated, allocated);
	return -ENOSPC;
	}
	if (next != previous - 1 && IS_CONTIGUOUS(*node))
	{
	/* it's a pity, but we are not able to keep the file contiguous
	anymore */
	make_noncontiguous(ef, node->start_cluster, previous);
	node->flags &= ~EXFAT_ATTRIB_CONTIGUOUS;
	node->flags \|= EXFAT_ATTRIB_DIRTY;
	}
	set_next_cluster(ef, IS_CONTIGUOUS(*node), previous, next);
	previous = next;
	allocated++;
	}

	set_next_cluster(ef, IS_CONTIGUOUS(*node), previous, EXFAT_CLUSTER_END);
	return 0;
	}

	static int shrink_file(struct exfat* ef, struct exfat_node* node,
	uint32_t current, uint32_t difference)
	{
	cluster_t previous;
	cluster_t next;

	if (difference == 0)
	exfat_bug("zero difference passed");
	if (node->start_cluster == EXFAT_CLUSTER_FREE)
	exfat_bug("unable to shrink empty file (%u clusters)", current);
	if (current < difference)
	exfat_bug("file underflow (%u < %u)", current, difference);

	/* crop the file */
	if (current > difference)
	{
	cluster_t last = exfat_advance_cluster(ef, node,
	current - difference - 1);
	if (CLUSTER_INVALID(last))
	{
	exfat_error("invalid cluster 0x%x while shrinking", last);
	return -EIO;
	}
	previous = exfat_next_cluster(ef, node, last);
	set_next_cluster(ef, IS_CONTIGUOUS(*node), last, EXFAT_CLUSTER_END);
	}
	else
	{
	previous = node->start_cluster;
	node->start_cluster = EXFAT_CLUSTER_FREE;
	}
	node->fptr_index = 0;
	node->fptr_cluster = node->start_cluster;

	/* free remaining clusters */
	while (difference--)
	{
	if (CLUSTER_INVALID(previous))
	{
	exfat_error("invalid cluster 0x%x while freeing after shrink",
	previous);
	return -EIO;
	}
	next = exfat_next_cluster(ef, node, previous);
	set_next_cluster(ef, IS_CONTIGUOUS(*node), previous,
	EXFAT_CLUSTER_FREE);
	free_cluster(ef, previous);
	previous = next;
	}
	return 0;
	}

	static void erase_raw(struct exfat* ef, size_t size, off64_t offset)
	{
	exfat_pwrite(ef->dev, ef->zero_cluster, size, offset);
	}

	static int erase_range(struct exfat* ef, struct exfat_node* node,
	uint64_t begin, uint64_t end)
	{
	uint64_t cluster_boundary;
	cluster_t cluster;

	if (begin >= end)
	return 0;

	cluster_boundary = (begin \| (CLUSTER_SIZE(*ef->sb) - 1)) + 1;
	cluster = exfat_advance_cluster(ef, node,
	begin / CLUSTER_SIZE(*ef->sb));
	if (CLUSTER_INVALID(cluster))
	{
	exfat_error("invalid cluster 0x%x while erasing", cluster);
	return -EIO;
	}
	/* erase from the beginning to the closest cluster boundary */
	erase_raw(ef, MIN(cluster_boundary, end) - begin,
	exfat_c2o(ef, cluster) + begin % CLUSTER_SIZE(*ef->sb));
	/* erase whole clusters */
	while (cluster_boundary < end)
	{
	cluster = exfat_next_cluster(ef, node, cluster);
	/* the cluster cannot be invalid because we have just allocated it */
	if (CLUSTER_INVALID(cluster))
	exfat_bug("invalid cluster 0x%x after allocation", cluster);
	erase_raw(ef, CLUSTER_SIZE(*ef->sb), exfat_c2o(ef, cluster));
	cluster_boundary += CLUSTER_SIZE(*ef->sb);
	}
	return 0;
	}

	int exfat_truncate(struct exfat* ef, struct exfat_node* node, uint64_t size)
	{
	uint32_t c1 = bytes2clusters(ef, node->size);
	uint32_t c2 = bytes2clusters(ef, size);
	int rc = 0;

	if (node->references == 0 && node->parent)
	exfat_bug("no references, node changes can be lost");

	if (node->size == size)
	return 0;

	if (c1 < c2)
	rc = grow_file(ef, node, c1, c2 - c1);
	else if (c1 > c2)
	rc = shrink_file(ef, node, c1, c1 - c2);

	if (rc != 0)
	return rc;

	rc = erase_range(ef, node, node->size, size);
	if (rc != 0)
	return rc;

	exfat_update_mtime(node);
	node->size = size;
	node->flags \|= EXFAT_ATTRIB_DIRTY;
	return 0;
	}

	uint32_t exfat_count_free_clusters(const struct exfat* ef)
	{
	uint32_t free_clusters = 0;
	uint32_t i;

	for (i = 0; i < ef->cmap.size; i++)
	if (BMAP_GET(ef->cmap.chunk, i) == 0)
	free_clusters++;
	return free_clusters;
	}

	static int find_used_clusters(const struct exfat* ef,
	cluster_t* a, cluster_t* b)
	{
	const cluster_t end = le32_to_cpu(ef->sb->cluster_count);

	/* find first used cluster */
	for (a = b + 1; a < end; (a)++)
	if (BMAP_GET(ef->cmap.chunk, *a - EXFAT_FIRST_DATA_CLUSTER))
	break;
	if (*a >= end)
	return 1;

	/* find last contiguous used cluster */
	for (b = a; b < end; (b)++)
	if (BMAP_GET(ef->cmap.chunk, *b - EXFAT_FIRST_DATA_CLUSTER) == 0)
	{
	(*b)--;
	break;
	}

	return 0;
	}

	int exfat_find_used_sectors(const struct exfat* ef, off64_t* a, off64_t* b)
	{
	cluster_t ca, cb;

	if (a == 0 && b == 0)
	ca = cb = EXFAT_FIRST_DATA_CLUSTER - 1;
	else
	{
	ca = s2c(ef, *a);
	cb = s2c(ef, *b);
	}
	if (find_used_clusters(ef, &ca, &cb) != 0)
	return 1;
	if (a != 0 \|\| b != 0)
	*a = c2s(ef, ca);
	b = c2s(ef, cb) + (CLUSTER_SIZE(ef->sb) - 1) / SECTOR_SIZE(*ef->sb);
	return 0;
	}