#include <kernel/iovec.h>
#include <kernel/libc/stdio.h>
#include <kernel/object.h>
#include <kernel/panic.h>
#include <kernel/printk.h>
#include <kernel/util.h>
#include <kernel/vm-object.h>
#include <kernel/vm-region.h>
#include <mango/status.h>

/*** STATIC DATA + MACROS *****************************************************/

#undef ASLR

#define INVALID_OFFSET ((off_t) - 1)

#ifdef ASLR
#define region_find_free_area(region, length)                                  \
	region_find_free_area_random(region, length)
#else
#define region_find_free_area(region, length)                                  \
	region_find_free_area_linear(region, length)
#endif

/* iterates over a range of mapped virtual memory in a region, and provides
 * a moving buffer through which the memory can be accessed */
struct vm_iterator {
	struct vm_region *it_region;
	struct vm_region_mapping *it_mapping;
	virt_addr_t it_base;
	vm_prot_t it_prot;
	void *it_buf;
	size_t it_max;
};

/* iterates recursively over the entries in a region */
struct entry_iterator {
	struct vm_region *it_root;
	struct vm_region_entry *it_entry;
	/* depth of it_entry relative to it_root */
	unsigned int it_depth;
};

enum search_direction {
	SEARCH_LEFT,
	SEARCH_RIGHT,
};

#define VM_REGION_CAST(p)                                                      \
	OBJECT_C_CAST(struct vm_region, vr_base, &vm_region_type, p)

static struct object_type vm_region_type = {
	.ob_name = "vm-region",
	.ob_size = sizeof(struct vm_region),
	.ob_header_offset = offsetof(struct vm_region, vr_base),
};

static struct vm_cache mapping_cache = {
	.c_name = "vm-region-mapping",
	.c_obj_size = sizeof(struct vm_region_mapping),
};

/*** INTERNAL UTILITY FUNCTION ************************************************/

static struct vm_region *region_from_entry(struct vm_region_entry *entry)
{
	if (!entry || entry->e_type != VM_REGION_ENTRY_REGION) {
		return NULL;
	}

	return BTREE_CONTAINER(struct vm_region, vr_entry, entry);
}

static struct vm_region_mapping *mapping_from_entry(
	struct vm_region_entry *entry)
{
	if (!entry || entry->e_type != VM_REGION_ENTRY_MAPPING) {
		return NULL;
	}

	return BTREE_CONTAINER(struct vm_region_mapping, m_entry, entry);
}

static virt_addr_t entry_absolute_address(const struct vm_region_entry *entry)
{
	virt_addr_t result = 0;
	while (entry) {
		result += entry->e_offset;
		entry = entry->e_parent;
	}

	return result;
}

static void region_put_entry(
	struct vm_region *parent,
	struct vm_region_entry *child)
{
	struct btree_node *cur = parent->vr_entries.b_root;
	if (!cur) {
		parent->vr_entries.b_root = &child->e_node;
		btree_insert_fixup(&parent->vr_entries, &child->e_node);
		return;
	}

	off_t child_base = child->e_offset;
	off_t child_limit = child_base + child->e_size - 1;

	while (cur) {
		struct vm_region_entry *cur_entry
			= BTREE_CONTAINER(struct vm_region_entry, e_node, cur);

		struct btree_node *next = NULL;
		off_t cur_base = cur_entry->e_offset;
		off_t cur_limit = cur_base + cur_entry->e_size - 1;

		if (child_limit < cur_base) {
			next = btree_left(cur);
		} else if (child_base > cur_limit) {
			next = btree_right(cur);
		} else {
			panic("tried to add an overlapping entry to vm-region");
		}

		if (next) {
			cur = next;
			continue;
		}

		if (child_limit < cur_base) {
			btree_put_left(cur, &child->e_node);
		} else {
			btree_put_right(cur, &child->e_node);
		}

		btree_insert_fixup(&parent->vr_entries, &child->e_node);
		break;
	}
}

/* find the child entry that covers the specified offset.
 * DOES NOT search recursively! */
static struct vm_region_entry *region_get_entry(
	struct vm_region *region,
	off_t offset,
	size_t len)
{
	struct btree_node *cur = region->vr_entries.b_root;
	if (!cur) {
		return NULL;
	}

	struct vm_region_entry *result = NULL;

	off_t base = offset, limit = offset + len - 1;

	while (cur) {
		struct vm_region_entry *child
			= BTREE_CONTAINER(struct vm_region_entry, e_node, cur);

		struct btree_node *next = NULL;
		off_t child_base = child->e_offset;
		off_t child_limit = child->e_offset + child->e_size - 1;

		if (limit < child_base) {
			next = btree_left(cur);
		} else if (base > child_limit) {
			next = btree_right(cur);
		} else {
			result = child;
			break;
		}

		cur = next;
	}

	return result;
}

/* find the child region that covers the area [*offp,len]. searches recursively
 * the value in `offp` is updated to the offset of the returned entry relative
 * to its parent */
static struct vm_region *region_get_child_region_recursive(
	struct vm_region *region,
	off_t *offp,
	size_t len)
{
	off_t offset = *offp;
	if (offset >= region->vr_entry.e_size) {
		return NULL;
	}

	while (1) {
		struct vm_region_entry *next
			= region_get_entry(region, offset, len);

		struct vm_region *next_region = region_from_entry(next);
		if (next_region) {
			offset -= next->e_offset;
			region = next_region;
		} else {
			break;
		}
	}

	*offp = offset;
	return region;
}

static struct vm_region_mapping *region_get_mapping_recursive(
	struct vm_region *region,
	off_t *offp,
	size_t len)
{
	off_t offset = *offp;
	region = region_get_child_region_recursive(region, &offset, len);
	if (!region) {
		return NULL;
	}

	struct vm_region_entry *entry = region_get_entry(region, offset, len);
	*offp = offset;

	return mapping_from_entry(entry);
}

static off_t generate_random_address(
	off_t area_base,
	size_t area_length,
	size_t target_length)
{
	size_t random_range = area_length - target_length;

	off_t offset = 0;
	fill_random(&offset, sizeof offset);

	offset %= random_range;
	return area_base + offset;
}

static struct vm_region_entry *region_get_random_entry(struct vm_region *region)
{
	enum {
		STEP_LEFT = 0,
		STEP_RIGHT = 1,
		STEP_FINISH = 2,
	} step;

	struct btree_node *result = NULL;
	struct btree_node *cur = region->vr_entries.b_root;
	if (!cur) {
		return NULL;
	}

	while (1) {
		unsigned long r;
		fill_random(&r, sizeof r);

		struct btree_node *next = NULL;

		step = r % 3;
		switch (step) {
		case STEP_LEFT:
			next = btree_left(cur);
			break;
		case STEP_RIGHT:
			next = btree_right(cur);
			break;
		case STEP_FINISH:
			result = cur;
			break;
		default:
			return NULL;
		}

		if (!next) {
			result = cur;
			break;
		}

		cur = next;
	}

	if (!result) {
		return NULL;
	}

	return BTREE_CONTAINER(struct vm_region_entry, e_node, result);
}

static virt_addr_t region_find_free_area_ex(
	struct vm_region *region,
	size_t target_length,
	struct btree_node *start,
	enum search_direction direction,
	bool random)
{
	if (region->vr_entry.e_size < target_length) {
		return 0;
	}

	struct btree_node *left_node = NULL, *right_node = NULL;

	switch (direction) {
	case SEARCH_LEFT:
		right_node = start;
		left_node = start ? btree_prev(start) : NULL;
		break;
	case SEARCH_RIGHT:
		left_node = start;
		right_node = start ? btree_next(start) : NULL;
		break;
	default:
		return 0;
	}

	if (!left_node && !right_node) {
		return 0;
	}

	while (1) {
		struct vm_region_entry *left = BTREE_CONTAINER(
			struct vm_region_entry,
			e_node,
			left_node);
		struct vm_region_entry *right = BTREE_CONTAINER(
			struct vm_region_entry,
			e_node,
			right_node);

		/* addresses of the first and last free bytes in the area
		 * respectively. */
		off_t area_base, area_limit;
		if (left && right) {
			area_base = left->e_offset + left->e_size;
			area_limit = right->e_offset - 1;
		} else if (right) {
			area_base = region->vr_entry.e_offset;
			area_limit = left->e_offset - 1;
		} else if (left) {
			area_base = left->e_offset + left->e_size;
			area_limit = region->vr_entry.e_offset
			           + region->vr_entry.e_size - 1;
		} else {
			return 0;
		}

		area_base &= ~VM_PAGE_MASK;
		size_t area_size = 0;
		if (area_limit >= area_base) {
			area_size = area_limit - area_base + 1;
		}

		if (area_size >= target_length) {
			if (random) {
				area_base = generate_random_address(
					area_base,
					area_size,
					target_length);
				area_base &= ~VM_PAGE_MASK;
			}

			return area_base;
		}

		if (direction == SEARCH_RIGHT) {
			left_node = right_node;
			right_node = btree_next(right_node);
		} else {
			right_node = left_node;
			left_node = btree_prev(right_node);
		}
	}

	return 0;
}

static off_t region_find_free_area_linear(
	struct vm_region *region,
	size_t target_length)
{
	if (!region->vr_entries.b_root) {
		return 0;
	}

	return region_find_free_area_ex(
		region,
		target_length,
		btree_first(&region->vr_entries),
		SEARCH_RIGHT,
		false);
}

static off_t region_find_free_area_random(
	struct vm_region *region,
	size_t target_length)
{
	if (!region->vr_entries.b_root) {
		off_t offset = generate_random_address(
			0,
			region->vr_entry.e_size,
			target_length);
		return offset & ~VM_PAGE_MASK;
	}

	int tmp = 0;
	struct vm_region_entry *basis = region_get_random_entry(region);

	fill_random(&tmp, sizeof tmp);
	enum search_direction direction = tmp % 2;

	return region_find_free_area_ex(
		region,
		target_length,
		&basis->e_node,
		direction,
		true);
}

static bool region_is_area_free(
	const struct vm_region *region,
	off_t base,
	size_t len)
{
	off_t limit = base + len - 1;

	if (base >= region->vr_entry.e_size) {
		return false;
	}

	if (limit >= region->vr_entry.e_size) {
		return false;
	}

	struct btree_node *cur = region->vr_entries.b_root;
	if (!cur) {
		return true;
	}

	while (cur) {
		struct vm_region_entry *entry
			= BTREE_CONTAINER(struct vm_region_entry, e_node, cur);

		struct btree_node *next = NULL;
		off_t entry_limit = entry->e_offset + entry->e_size - 1;

		if (base > entry_limit) {
			next = btree_right(cur);
		} else if (limit < entry->e_offset) {
			next = btree_left(cur);
		} else {
			return false;
		}

		cur = next;
	}

	return true;
}

static kern_status_t region_validate_allocation(
	struct vm_region *parent,
	vm_prot_t prot,
	off_t *offp,
	size_t len)
{
	off_t offset = *offp;

	if ((prot & parent->vr_prot) != prot) {
		/* child region protection must match or be a
		 * subset of parent region protection */
		return KERN_INVALID_ARGUMENT;
	}

	if (offset == VM_REGION_ANY_OFFSET) {
		offset = region_find_free_area(parent, len);
		*offp = offset;
		return (offset == INVALID_OFFSET) ? KERN_NO_MEMORY : KERN_OK;
	}

	offset &= ~VM_PAGE_MASK;

	if (!region_is_area_free(parent, offset, len)) {
		return KERN_INVALID_ARGUMENT;
	}

	*offp = offset;
	return KERN_OK;
}

static void vm_iterator_begin(
	struct vm_iterator *it,
	struct vm_region *region,
	virt_addr_t base,
	vm_prot_t prot)
{
	memset(it, 0x0, sizeof *it);
	it->it_base = base;
	it->it_region = region;
	it->it_prot = prot;

	off_t offset = base - vm_region_get_base_address(region);
	it->it_mapping = region_get_mapping_recursive(region, &offset, 1);
	if (!it->it_mapping || (it->it_mapping->m_prot & prot) != prot) {
		return;
	}

	off_t object_offset = offset - it->it_mapping->m_entry.e_offset
	                    + it->it_mapping->m_object_offset;
	struct vm_page *pg = NULL;
	if (prot & VM_PROT_WRITE) {
		pg = vm_object_alloc_page(
			it->it_mapping->m_object,
			object_offset,
			VM_PAGE_4K);
	} else {
		pg = vm_object_get_page(
			it->it_mapping->m_object,
			object_offset);
	}

	if (!pg) {
		return;
	}

	void *buffer_base = vm_page_get_vaddr(pg);
	phys_addr_t pg_addr = vm_page_get_paddr(pg);
	size_t buffer_size = vm_page_get_size_bytes(pg);

	while (1) {
		struct btree_node *next_node = btree_next(&pg->p_bnode);
		struct vm_page *next
			= BTREE_CONTAINER(struct vm_page, p_bnode, next_node);
		if (!next) {
			break;
		}

		phys_addr_t next_addr = vm_page_get_paddr(next);
		if (pg_addr + vm_page_get_size_bytes(pg) != next_addr) {
			break;
		}

		pg = next;
		pg_addr = next_addr;
		buffer_size += vm_page_get_size_bytes(next);
	}

	it->it_buf = (char *)buffer_base + (object_offset & VM_PAGE_MASK);
	it->it_max = buffer_size - (object_offset & VM_PAGE_MASK);
}

static kern_status_t vm_iterator_seek(struct vm_iterator *it, size_t nr_bytes)
{
	if (nr_bytes < it->it_max) {
		it->it_base += nr_bytes;
		it->it_buf = (char *)it->it_buf + nr_bytes;
		it->it_max -= nr_bytes;
		return KERN_OK;
	}

	it->it_base += nr_bytes;
	off_t offset = it->it_base - vm_region_get_base_address(it->it_region);

	struct vm_region_mapping *next_mapping
		= region_get_mapping_recursive(it->it_region, &offset, 1);
	if (!next_mapping) {
		it->it_buf = NULL;
		it->it_max = 0;
		return KERN_MEMORY_FAULT;
	}

	if ((next_mapping->m_prot & it->it_prot) != it->it_prot) {
		it->it_buf = NULL;
		it->it_max = 0;
		return KERN_MEMORY_FAULT;
	}

	off_t object_offset = offset - it->it_mapping->m_entry.e_offset
	                    + it->it_mapping->m_object_offset;
	struct vm_page *pg = NULL;
	if (it->it_prot & VM_PROT_WRITE) {
		pg = vm_object_alloc_page(
			it->it_mapping->m_object,
			object_offset,
			VM_PAGE_4K);
	} else {
		pg = vm_object_get_page(
			it->it_mapping->m_object,
			object_offset);
	}

	if (!pg) {
		return KERN_NO_MEMORY;
	}

	void *buffer_base = vm_page_get_vaddr(pg);
	phys_addr_t pg_addr = vm_page_get_paddr(pg);
	size_t buffer_size = vm_page_get_size_bytes(pg);

	while (1) {
		struct btree_node *next_node = btree_next(&pg->p_bnode);
		struct vm_page *next
			= BTREE_CONTAINER(struct vm_page, p_bnode, next_node);
		if (!next) {
			break;
		}

		phys_addr_t next_addr = vm_page_get_paddr(next);
		if (pg_addr + vm_page_get_size_bytes(pg) != next_addr) {
			break;
		}

		pg = next;
		pg_addr = next_addr;
		buffer_size += vm_page_get_size_bytes(next);
	}

	it->it_buf = (char *)buffer_base + (object_offset & VM_PAGE_MASK);
	it->it_max = buffer_size;
	return KERN_OK;
}

static void entry_iterator_begin(
	struct entry_iterator *it,
	struct vm_region *root)
{
	memset(it, 0x0, sizeof *it);
	it->it_root = root;
	it->it_entry = &root->vr_entry;
}

static void entry_iterator_move_next(struct entry_iterator *it)
{
	struct vm_region *region = region_from_entry(it->it_entry);
	bool has_children = (region && !btree_empty(&region->vr_entries));

	if (has_children) {
		/* visit the first child */
		struct btree_node *node = btree_first(&region->vr_entries);
		struct vm_region_entry *entry
			= BTREE_CONTAINER(struct vm_region_entry, e_node, node);
		it->it_depth++;
		it->it_entry = entry;
		return;
	}

	/* go back up until we find a right sibling. */
	struct vm_region_entry *cur = it->it_entry;

	while (1) {
		struct btree_node *sibling = btree_next(&cur->e_node);
		if (sibling) {
			it->it_entry = BTREE_CONTAINER(
				struct vm_region_entry,
				e_node,
				sibling);
			return;
		}

		if (cur == &it->it_root->vr_entry) {
			it->it_entry = NULL;
			return;
		}

		struct vm_region_entry *parent_entry = cur->e_parent;
		struct vm_region *parent = region_from_entry(parent_entry);

		if (!parent) {
			it->it_entry = NULL;
			return;
		}

		it->it_depth--;
		cur = parent_entry;
	}
}

static void mapping_iterator_begin(
	struct entry_iterator *it,
	struct vm_region *root,
	off_t offset,
	size_t length,
	off_t *offp)
{
	entry_iterator_begin(it, root);
	while (it->it_entry) {
		off_t base = entry_absolute_address(it->it_entry)
		           - root->vr_entry.e_offset;
		off_t limit = base + it->it_entry->e_size - 1;

		if (it->it_entry->e_type == VM_REGION_ENTRY_MAPPING) {
			if (offset >= base && offset <= limit) {
				*offp = base;
				return;
			}

			if (offset + length >= base
			    && offset + length <= limit) {
				*offp = base;
				return;
			}
		}

		entry_iterator_move_next(it);
	}
}

static void mapping_iterator_move_next(
	struct entry_iterator *it,
	off_t offset,
	size_t length,
	off_t *offp)
{
	do {
		entry_iterator_move_next(it);
	} while (it->it_entry
	         && it->it_entry->e_type != VM_REGION_ENTRY_MAPPING);

	if (!it->it_entry) {
		return;
	}

	off_t base = entry_absolute_address(it->it_entry)
	           - it->it_root->vr_entry.e_offset;

	if (base >= offset + length) {
		it->it_entry = NULL;
	} else {
		*offp = base;
	}
}

/*** PUBLIC API ***************************************************************/

kern_status_t vm_region_type_init(void)
{
	vm_cache_init(&mapping_cache);
	return object_type_register(&vm_region_type);
}

struct vm_region *vm_region_cast(struct object *obj)
{
	return VM_REGION_CAST(obj);
}

kern_status_t vm_region_create(
	struct vm_region *parent,
	const char *name,
	size_t name_len,
	off_t offset,
	size_t region_len,
	vm_prot_t prot,
	struct vm_region **out)
{
	if (!offset || !region_len) {
		return KERN_INVALID_ARGUMENT;
	}

	if (region_len & VM_PAGE_MASK) {
		region_len &= ~VM_PAGE_MASK;
		region_len += VM_PAGE_SIZE;
	}

	kern_status_t status = KERN_OK;
	if (parent) {
		status = region_validate_allocation(
			parent,
			prot,
			&offset,
			region_len);
	}

	if (status != KERN_OK) {
		return status;
	}

	struct object *region_object = object_create(&vm_region_type);
	if (!region_object) {
		return KERN_NO_MEMORY;
	}

	struct vm_region *region = VM_REGION_CAST(region_object);

	region->vr_prot = prot;
	region->vr_entry.e_type = VM_REGION_ENTRY_REGION;
	region->vr_entry.e_offset = offset;
	region->vr_entry.e_size = region_len;

#ifdef TRACE
	tracek("creating sub-region at [%llx-%llx]",
	       offset,
	       offset + region_len);
#endif

	if (parent) {
		region->vr_entry.e_parent = &parent->vr_entry;
		region->vr_pmap = parent->vr_pmap;
		region_put_entry(parent, &region->vr_entry);
	}

	if (name && name_len) {
		name_len = MIN(sizeof region->vr_name - 1, name_len);
		memcpy(region->vr_name, name, name_len);
		region->vr_name[name_len] = '\0';
	}

	*out = region;
	return KERN_OK;
}

kern_status_t vm_region_map_object(
	struct vm_region *region,
	off_t region_offset,
	struct vm_object *object,
	off_t object_offset,
	size_t length,
	vm_prot_t prot,
	virt_addr_t *out)
{
	object_offset &= ~VM_PAGE_MASK;

	if (region_offset != VM_REGION_ANY_OFFSET) {
		off_t limit = region_offset + length;

		if (region_offset & VM_PAGE_MASK) {
			region_offset &= ~VM_PAGE_MASK;
		}

		if (limit & VM_PAGE_MASK) {
			limit &= ~VM_PAGE_MASK;
			limit += VM_PAGE_SIZE;
		}

		length = limit - region_offset;
	}

	if (length & VM_PAGE_MASK) {
		length &= ~VM_PAGE_MASK;
		length += VM_PAGE_SIZE;
	}

	if (!region || !object) {
		return KERN_INVALID_ARGUMENT;
	}

	if ((prot & region->vr_prot) != prot) {
		return KERN_INVALID_ARGUMENT;
	}

	if ((prot & object->vo_prot) != prot) {
		return KERN_INVALID_ARGUMENT;
	}

	if (!length || object_offset + length > object->vo_size) {
		return KERN_INVALID_ARGUMENT;
	}

	if (region_offset != VM_REGION_ANY_OFFSET) {
		region = region_get_child_region_recursive(
			region,
			&region_offset,
			length);
	}

	if (!region) {
		return KERN_INVALID_ARGUMENT;
	}

	if (region_offset == VM_REGION_ANY_OFFSET) {
		region_offset = region_find_free_area(region, length);

		if (region_offset == INVALID_OFFSET) {
			return KERN_NO_MEMORY;
		}
	} else if (!region_is_area_free(region, region_offset, length)) {
		return KERN_INVALID_ARGUMENT;
	}

	tracek("vm_region_map_object(%s, %zx, %s, %zx, %zx, %x, %p)",
	       region->vr_name,
	       region_offset,
	       object->vo_name,
	       object_offset,
	       length,
	       prot,
	       out);

	struct vm_region_mapping *mapping
		= vm_cache_alloc(&mapping_cache, VM_NORMAL);
	if (!mapping) {
		return KERN_NO_MEMORY;
	}

	mapping->m_object = object;
	mapping->m_prot = prot;
	mapping->m_object_offset = object_offset;
	mapping->m_entry.e_type = VM_REGION_ENTRY_MAPPING;
	mapping->m_entry.e_parent = &region->vr_entry;
	mapping->m_entry.e_offset = region_offset;
	mapping->m_entry.e_size = length;

#ifdef TRACE
	virt_addr_t abs_base = entry_absolute_address(&mapping->m_entry);
	tracek("mapping %s at [%llx-%llx]",
	       object->vo_name,
	       abs_base,
	       abs_base + length);
#endif
	region_put_entry(region, &mapping->m_entry);
	queue_push_back(&object->vo_mappings, &mapping->m_object_entry);

	if (out) {
		*out = entry_absolute_address(&mapping->m_entry);
	}

	return KERN_OK;
}

/* unmap some pages in the middle of a mapping, splitting it into two separate
 * mappings */
static kern_status_t split_mapping(
	struct vm_region_mapping *mapping,
	struct vm_region *root,
	off_t mapping_offset,
	off_t unmap_offset,
	off_t unmap_limit)
{
	tracek("split mapping [%zx-%zx] subtract [%zx-%zx]",
	       mapping_offset,
	       mapping_offset + mapping->m_entry.e_size,
	       unmap_offset,
	       unmap_limit);

	off_t mapping_limit = mapping_offset + mapping->m_entry.e_size;

	struct vm_region *parent = region_from_entry(mapping->m_entry.e_parent);
	struct vm_region_mapping *left = mapping;
	struct vm_region_mapping *right
		= vm_cache_alloc(&mapping_cache, VM_NORMAL);
	if (!right) {
		return KERN_NO_MEMORY;
	}

	off_t left_offset = mapping->m_entry.e_offset;
	off_t right_offset = unmap_limit - mapping_offset;
	off_t left_object_offset = mapping->m_object_offset;
	size_t left_length = unmap_offset - mapping_offset;
	size_t right_length = mapping_limit - unmap_limit;
	off_t right_object_offset = mapping->m_object_offset
	                          + mapping->m_entry.e_size - right_length;

	tracek("mapping=[%zx-%zx]->[%zx-%zx]",
	       mapping_offset,
	       mapping_limit,
	       mapping->m_object_offset,
	       mapping->m_object_offset + mapping->m_entry.e_size);
	tracek("left=[%zx-%zx]->[%zx-%zx], right=[%zx-%zx]->[%zx-%zx]",
	       left_offset,
	       left_offset + left_length,
	       left_object_offset,
	       left_object_offset + left_length,
	       right_offset,
	       right_offset + right_length,
	       right_object_offset,
	       right_object_offset + right_length);

	left->m_object_offset = left_object_offset;
	left->m_entry.e_offset = left_offset;
	left->m_entry.e_size = left_length;

	right->m_object = left->m_object;
	right->m_prot = left->m_prot;
	right->m_entry.e_type = VM_REGION_ENTRY_MAPPING;
	right->m_entry.e_parent = left->m_entry.e_parent;

	right->m_object_offset = right_object_offset;
	right->m_entry.e_offset = right_offset;
	right->m_entry.e_size = right_length;

	virt_addr_t unmap_base = root->vr_entry.e_offset + unmap_offset;
	size_t unmap_length = unmap_limit - unmap_offset;

	for (size_t i = 0; i < unmap_length; i += VM_PAGE_SIZE) {
		tracek("unmapping %zx", unmap_base + i);
		pmap_remove(root->vr_pmap, unmap_base + i);
	}

	region_put_entry(parent, &right->m_entry);

	return KERN_OK;
}

/* unmap some pages from the left-side of a mapping to somewhere in the
 * middle. */
static kern_status_t left_reduce_mapping(
	struct vm_region_mapping *mapping,
	struct vm_region *root,
	off_t mapping_offset,
	off_t unmap_offset,
	off_t unmap_limit)
{
	/* unmap_limit falls somwwhere between mapping_offset and
	 * mapping_offset+length */
	tracek("left reduce mapping [%zx-%zx] subtract [%zx-%zx]",
	       mapping_offset,
	       mapping_offset + mapping->m_entry.e_size,
	       unmap_offset,
	       unmap_limit);

	virt_addr_t base = root->vr_entry.e_offset + mapping_offset;
	off_t limit = mapping_offset + mapping->m_entry.e_size;
	size_t length = mapping->m_entry.e_size - (limit - unmap_limit);
	tracek(" unmapping %zx-%zx (%zx bytes)", base, base + length, length);

	for (size_t i = 0; i < length; i += VM_PAGE_SIZE) {
		pmap_remove(root->vr_pmap, base + i);
	}

	mapping->m_entry.e_offset += length;
	mapping->m_object_offset += length;
	mapping->m_entry.e_size -= length;

	return KERN_OK;
}

/* unmap some pages from the middle of a mapping to the right-side. */
static kern_status_t right_reduce_mapping(
	struct vm_region_mapping *mapping,
	struct vm_region *root,
	off_t mapping_offset,
	off_t unmap_offset,
	off_t unmap_limit)
{
	/* unmap_base falls somwwhere between mapping_offset and
	 * mapping_offset+length */
	tracek("right reduce mapping [%zx-%zx] subtract [%zx-%zx]",
	       mapping_offset,
	       mapping_offset + mapping->m_entry.e_size,
	       unmap_offset,
	       unmap_limit);

	virt_addr_t base = root->vr_entry.e_offset + unmap_offset;
	off_t limit = mapping_offset + mapping->m_entry.e_size;
	size_t length = limit - unmap_offset;
	tracek(" unmapping %zx-%zx (%zx bytes)", base, base + length, length);

	for (size_t i = 0; i < length; i += VM_PAGE_SIZE) {
		pmap_remove(root->vr_pmap, base + i);
	}

	mapping->m_entry.e_size -= length;

	return KERN_OK;
}

/* completely unmap and delete an entire mapping */
static kern_status_t delete_mapping(
	struct vm_region_mapping *mapping,
	struct vm_region *root,
	off_t mapping_offset)
{
	virt_addr_t base = root->vr_entry.e_offset + mapping_offset;
	tracek("delete mapping [%zx-%zx]",
	       base,
	       base + mapping->m_entry.e_size);

	for (size_t i = 0; i < mapping->m_entry.e_size; i += VM_PAGE_SIZE) {
		pmap_remove(root->vr_pmap, base + i);
	}

	struct vm_region *parent = region_from_entry(mapping->m_entry.e_parent);

	queue_delete(&mapping->m_object->vo_mappings, &mapping->m_object_entry);
	btree_delete(&parent->vr_entries, &mapping->m_entry.e_node);

	vm_cache_free(&mapping_cache, mapping);

	return KERN_OK;
}

kern_status_t vm_region_unmap(
	struct vm_region *region,
	off_t unmap_area_offset,
	size_t unmap_area_length)
{
	kern_status_t status = KERN_OK;
	struct entry_iterator it;
	off_t unmap_area_limit = unmap_area_offset + unmap_area_length;
	tracek("unmapping %zx-%zx", unmap_area_offset, unmap_area_limit);
	off_t tmp = 0;

	mapping_iterator_begin(
		&it,
		region,
		unmap_area_offset,
		unmap_area_length,
		&tmp);
	while (it.it_entry) {
		struct vm_region_mapping *mapping
			= mapping_from_entry(it.it_entry);
		off_t mapping_offset = tmp;
		off_t mapping_limit = mapping_offset + it.it_entry->e_size;

		mapping_iterator_move_next(
			&it,
			unmap_area_offset,
			unmap_area_length,
			&tmp);

		bool split
			= (unmap_area_offset > mapping_offset
		           && unmap_area_limit < mapping_limit);
		bool delete
			= (unmap_area_offset <= mapping_offset
		           && unmap_area_limit >= mapping_limit);
		bool left_reduce
			= (unmap_area_offset <= mapping_offset
		           && unmap_area_limit < mapping_limit);
		bool right_reduce
			= (unmap_area_offset > mapping_offset
		           && unmap_area_limit >= mapping_limit);

		if (split) {
			status = split_mapping(
				mapping,
				region,
				mapping_offset,
				unmap_area_offset,
				unmap_area_limit);
		} else if (delete) {
			status = delete_mapping(
				mapping,
				region,
				mapping_offset);
		} else if (left_reduce) {
			status = left_reduce_mapping(
				mapping,
				region,
				mapping_offset,
				unmap_area_offset,
				unmap_area_limit);
		} else if (right_reduce) {
			status = right_reduce_mapping(
				mapping,
				region,
				mapping_offset,
				unmap_area_offset,
				unmap_area_limit);
		} else {
			panic("don't know what to do with this mapping");
		}

		if (status != KERN_OK) {
			break;
		}
	}

	return status;
}

bool vm_region_validate_access(
	struct vm_region *region,
	virt_addr_t ptr,
	size_t len,
	vm_prot_t prot)
{
	if (len == 0) {
		return true;
	}

	if (ptr < region->vr_entry.e_offset) {
		return false;
	}

	off_t offset = ptr - region->vr_entry.e_offset;

	if (len >= region->vr_entry.e_size) {
		return false;
	}

	if (offset + len > region->vr_entry.e_size) {
		return false;
	}

	offset &= ~VM_PAGE_MASK;

	/* TODO improve this to not require a per-page loop */
	for (off_t i = 0; i < len; i += VM_PAGE_SIZE) {
		off_t x = offset + i;
		struct vm_region_mapping *mapping
			= region_get_mapping_recursive(
				region,
				&x,
				VM_PAGE_SIZE);
		if (!mapping) {
			return false;
		}

		if ((mapping->m_prot & prot) != prot) {
			return false;
		}
	}

	return true;
}

kern_status_t vm_region_demand_map(
	struct vm_region *region,
	virt_addr_t addr,
	enum pmap_fault_flags flags)
{
	addr &= ~VM_PAGE_MASK;
	if (addr < region->vr_entry.e_offset
	    || addr > region->vr_entry.e_offset + region->vr_entry.e_size) {
		return KERN_NO_ENTRY;
	}

	off_t region_offset = addr - region->vr_entry.e_offset;

	struct vm_region_mapping *mapping
		= region_get_mapping_recursive(region, &region_offset, 1);
	if (!mapping) {
		return KERN_NO_ENTRY;
	}

	off_t object_offset = region_offset - mapping->m_entry.e_offset
	                    + mapping->m_object_offset;

	tracek("vm: tried to access vm-object %s at offset=%05llx",
	       mapping->m_object->vo_name,
	       object_offset);

	struct vm_page *pg = vm_object_alloc_page(
		mapping->m_object,
		object_offset,
		VM_PAGE_4K);
	tracek("vm: mapping %07llx -> %10llx", vm_page_get_paddr(pg), addr);
	return pmap_add(
		region->vr_pmap,
		addr,
		vm_page_get_pfn(pg),
		mapping->m_prot,
		PMAP_NORMAL);
}

virt_addr_t vm_region_get_base_address(const struct vm_region *region)
{
	return entry_absolute_address(&region->vr_entry);
}

kern_status_t vm_region_read_kernel(
	struct vm_region *src_region,
	virt_addr_t src_ptr,
	size_t count,
	void *destp,
	size_t *nr_read)
{
	struct vm_iterator src;
	char *dest = destp;

	vm_iterator_begin(
		&src,
		src_region,
		src_ptr,
		VM_PROT_READ | VM_PROT_USER);

	kern_status_t status = KERN_OK;
	size_t r = 0;

	while (r < count && src.it_max) {
		size_t remaining = count - r;
		size_t to_move = MIN(src.it_max, remaining);
		memmove(dest, src.it_buf, to_move);

		status = vm_iterator_seek(&src, to_move);
		if (status != KERN_OK) {
			break;
		}

		r += to_move;
		dest += to_move;
	}

	if (nr_read) {
		*nr_read = r;
	}

	return status;
}

kern_status_t vm_region_memmove(
	struct vm_region *dest_region,
	virt_addr_t dest_ptr,
	struct vm_region *src_region,
	virt_addr_t src_ptr,
	size_t count,
	size_t *nr_moved)
{
	struct vm_iterator src, dest;
	vm_iterator_begin(
		&src,
		src_region,
		src_ptr,
		VM_PROT_READ | VM_PROT_USER);
	vm_iterator_begin(
		&dest,
		dest_region,
		dest_ptr,
		VM_PROT_WRITE | VM_PROT_USER);

	kern_status_t status = KERN_OK;
	size_t r = 0;

	while (count && src.it_max && dest.it_max) {
		size_t to_move = MIN(MIN(src.it_max, dest.it_max), count);
		memmove(dest.it_buf, src.it_buf, to_move);

		status = vm_iterator_seek(&src, to_move);
		if (status != KERN_OK) {
			break;
		}

		status = vm_iterator_seek(&dest, to_move);
		if (status != KERN_OK) {
			break;
		}

		count -= to_move;
		r += to_move;
	}

	if (nr_moved) {
		*nr_moved = r;
	}

	return status;
}

extern kern_status_t vm_region_memmove_v(
	struct vm_region *dest_region,
	size_t dest_offset,
	struct iovec *dest_vecs,
	size_t nr_dest_vecs,
	struct vm_region *src_region,
	size_t src_offset,
	const struct iovec *src_vecs,
	size_t nr_src_vecs,
	size_t bytes_to_move)
{
	struct iovec_iterator src, dest;
	iovec_iterator_begin_user(&src, src_region, src_vecs, nr_src_vecs);
	iovec_iterator_begin_user(&dest, dest_region, dest_vecs, nr_dest_vecs);

	iovec_iterator_seek(&src, src_offset);
	iovec_iterator_seek(&dest, dest_offset);

	while (bytes_to_move && src.it_len && dest.it_len) {
		size_t to_move
			= MIN(MIN(src.it_len, dest.it_len), bytes_to_move);

		kern_status_t status = vm_region_memmove(
			dest_region,
			dest.it_base,
			src_region,
			src.it_base,
			to_move,
			NULL);
		if (status != KERN_OK) {
			return status;
		}

		iovec_iterator_seek(&src, to_move);
		iovec_iterator_seek(&dest, to_move);
		bytes_to_move -= to_move;
	}

	return KERN_OK;
}

#ifdef TRACE
void vm_region_dump(struct vm_region *region)
{
	char s[128];
	size_t p = 0;

	struct entry_iterator it;
	entry_iterator_begin(&it, region);
	while (it.it_entry) {
		p = 0;

		for (unsigned int i = 0; i < it.it_depth; i++) {
			p += snprintf(s + p, sizeof s - p, "    ");
		}

		switch (it.it_entry->e_type) {
		case VM_REGION_ENTRY_REGION: {
			struct vm_region *child
				= region_from_entry(it.it_entry);
			p += snprintf(
				s + p,
				sizeof s - p,
				"-region [%zx-%zx] %s",
				child->vr_entry.e_offset,
				child->vr_entry.e_offset
					+ child->vr_entry.e_size,
				child->vr_name);
			break;
		}
		case VM_REGION_ENTRY_MAPPING: {
			struct vm_region_mapping *mapping
				= mapping_from_entry(it.it_entry);
			p += snprintf(
				s + p,
				sizeof s - p,
				"+mapping [%zx-%zx] %s",
				mapping->m_entry.e_offset,
				mapping->m_entry.e_offset
					+ mapping->m_entry.e_size,
				mapping->m_object->vo_name);
			break;
		default:
			break;
		}
		}

		tracek("%s", s);
		entry_iterator_move_next(&it);
	}
}
#endif