mango/kernel/handle.c

#include <kernel/handle.h>
#include <kernel/libc/string.h>
#include <kernel/object.h>
#include <kernel/sched.h>
#include <kernel/util.h>
#include <kernel/vm.h>

/* depth=3 gives a maximum of ~66.6 million handles */
#define MAX_TABLE_DEPTH  3
#define RESERVED_HANDLES 64

static struct vm_cache handle_table_cache = {
	.c_name = "handle_table",
	.c_obj_size = sizeof(struct handle_table),
};

struct handle_table *handle_table_create(void)
{
	if (!VM_CACHE_INITIALISED(&handle_table_cache)) {
		vm_cache_init(&handle_table_cache);
	}

	struct handle_table *out
		= vm_cache_alloc(&handle_table_cache, VM_NORMAL);
	if (!out) {
		return NULL;
	}

	memset(out, 0x0, sizeof *out);

	return out;
}

void handle_table_destroy(struct handle_table *tab)
{
}

static kern_status_t decode_handle_indices(
	kern_handle_t handle,
	unsigned int indices[MAX_TABLE_DEPTH])
{
	for (int i = 0; i < MAX_TABLE_DEPTH; i++) {
		unsigned int div = (i > 0 ? REFS_PER_TABLE : HANDLES_PER_TABLE);

		unsigned int v = handle % div;
		indices[MAX_TABLE_DEPTH - i - 1] = v;
		handle /= div;
	}

	return handle == 0 ? KERN_OK : KERN_INVALID_ARGUMENT;
}

static kern_status_t encode_handle_indices(
	unsigned int indices[MAX_TABLE_DEPTH],
	kern_handle_t *out_handle)
{
	kern_handle_t handle = 0;
	unsigned int mul = 1;

	for (int i = MAX_TABLE_DEPTH - 1; i >= 0; i--) {
		unsigned int v = indices[i] * mul;
		handle += v;
		mul *= REFS_PER_TABLE;
	}

	*out_handle = handle;
	return KERN_OK;
}

kern_status_t handle_table_alloc_handle(
	struct handle_table *tab,
	struct handle **out_slot,
	kern_handle_t *out_handle)
{
	int i;
	unsigned int indices[MAX_TABLE_DEPTH] = {0};
	static const unsigned int reserved_indices[MAX_TABLE_DEPTH] = {0};

	for (i = 0; i < MAX_TABLE_DEPTH - 1; i++) {
		unsigned int next_index = bitmap_lowest_clear(
			tab->t_subtables.t_subtable_map,
			REFS_PER_TABLE);

		if (next_index == BITMAP_NPOS) {
			return KERN_NO_ENTRY;
		}

		struct handle_table *next
			= tab->t_subtables.t_subtable_list[next_index];
		if (!next) {
			next = handle_table_create();
			tab->t_subtables.t_subtable_list[next_index] = next;
		}

		if (!next) {
			return KERN_NO_MEMORY;
		}

		indices[i] = next_index;
		tab = next;
	}

	if (memcmp(indices, reserved_indices, sizeof indices) == 0) {
		bitmap_fill(tab->t_handles.t_handle_map, RESERVED_HANDLES);
	}

	unsigned int handle_index = bitmap_lowest_clear(
		tab->t_handles.t_handle_map,
		HANDLES_PER_TABLE);
	if (handle_index == BITMAP_NPOS) {
		return KERN_NO_ENTRY;
	}

	bitmap_set(tab->t_handles.t_handle_map, handle_index);
	memset(&tab->t_handles.t_handle_list[handle_index],
	       0x0,
	       sizeof(struct handle));

	indices[i] = handle_index;

	*out_slot = &tab->t_handles.t_handle_list[handle_index];
	return encode_handle_indices(indices, out_handle);
}

kern_status_t handle_table_free_handle(
	struct handle_table *tab,
	kern_handle_t handle)
{
	unsigned int indices[MAX_TABLE_DEPTH];
	if (decode_handle_indices(handle, indices) != KERN_OK) {
		return KERN_NO_ENTRY;
	}

	int i;
	for (i = 0; i < MAX_TABLE_DEPTH - 1; i++) {
		struct handle_table *next
			= tab->t_subtables.t_subtable_list[indices[i]];
		if (!next) {
			return KERN_NO_ENTRY;
		}

		bitmap_clear(tab->t_subtables.t_subtable_map, indices[i]);
		tab = next;
	}

	unsigned int handle_index = indices[i];
	if (!bitmap_check(tab->t_handles.t_handle_map, handle_index)) {
		return KERN_NO_ENTRY;
	}

	bitmap_clear(tab->t_handles.t_handle_map, handle_index);
	struct handle *handle_entry
		= &tab->t_handles.t_handle_list[handle_index];

	if (handle_entry->h_object) {
		object_remove_handle(handle_entry->h_object);
	}

	memset(handle_entry, 0x0, sizeof *handle_entry);
	return KERN_OK;
}

struct handle *handle_table_get_handle(
	struct handle_table *tab,
	kern_handle_t handle)
{
	unsigned int indices[MAX_TABLE_DEPTH];
	if (decode_handle_indices(handle, indices) != KERN_OK) {
		return NULL;
	}

	int i;
	for (i = 0; i < MAX_TABLE_DEPTH - 1; i++) {
		struct handle_table *next
			= tab->t_subtables.t_subtable_list[indices[i]];
		if (!next) {
			return NULL;
		}

		tab = next;
	}

	unsigned int handle_index = indices[i];
	if (!bitmap_check(tab->t_handles.t_handle_map, handle_index)) {
		return NULL;
	}

	return &tab->t_handles.t_handle_list[handle_index];
}