assoc_array_priv.h

/* SPDX-License-Identifier: GPL-2.0-or-later */
/* Private definitions for the generic associative array implementation.
 *
 * See Documentation/core-api/assoc_array.rst for information.
 *
 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#ifndef _LINUX_ASSOC_ARRAY_PRIV_H
#define _LINUX_ASSOC_ARRAY_PRIV_H

#ifdef CONFIG_ASSOCIATIVE_ARRAY

#include <linux/assoc_array.h>

#define ASSOC_ARRAY_FAN_OUT		16	/* Number of slots per node */
#define ASSOC_ARRAY_FAN_MASK		(ASSOC_ARRAY_FAN_OUT - 1)
#define ASSOC_ARRAY_LEVEL_STEP		(ilog2(ASSOC_ARRAY_FAN_OUT))
#define ASSOC_ARRAY_LEVEL_STEP_MASK	(ASSOC_ARRAY_LEVEL_STEP - 1)
#define ASSOC_ARRAY_KEY_CHUNK_MASK	(ASSOC_ARRAY_KEY_CHUNK_SIZE - 1)
#define ASSOC_ARRAY_KEY_CHUNK_SHIFT	(ilog2(BITS_PER_LONG))

/*
 * Undefined type representing a pointer with type information in the bottom
 * two bits.
 */
struct assoc_array_ptr;

/*
 * An N-way node in the tree.
 *
 * Each slot contains one of four things:
 *
 *	(1) Nothing (NULL).
 *
 *	(2) A leaf object (pointer types 0).
 *
 *	(3) A next-level node (pointer type 1, subtype 0).
 *
 *	(4) A shortcut (pointer type 1, subtype 1).
 *
 * The tree is optimised for search-by-ID, but permits reasonable iteration
 * also.
 *
 * The tree is navigated by constructing an index key consisting of an array of
 * segments, where each segment is ilog2(ASSOC_ARRAY_FAN_OUT) bits in size.
 *
 * The segments correspond to levels of the tree (the first segment is used at
 * level 0, the second at level 1, etc.).
 */
struct assoc_array_node {
	struct assoc_array_ptr	*back_pointer;
	u8			parent_slot;
	struct assoc_array_ptr	*slots[ASSOC_ARRAY_FAN_OUT];
	unsigned long		nr_leaves_on_branch;
};

/*
 * A shortcut through the index space out to where a collection of nodes/leaves
 * with the same IDs live.
 */
struct assoc_array_shortcut {
	struct assoc_array_ptr	*back_pointer;
	int			parent_slot;
	int			skip_to_level;
	struct assoc_array_ptr	*next_node;
	unsigned long		index_key[];
};

/*
 * Preallocation cache.
 */
struct assoc_array_edit {
	struct rcu_head			rcu;
	struct assoc_array		*array;
	const struct assoc_array_ops	*ops;
	const struct assoc_array_ops	*ops_for_excised_subtree;
	struct assoc_array_ptr		*leaf;
	struct assoc_array_ptr		**leaf_p;
	struct assoc_array_ptr		*dead_leaf;
	struct assoc_array_ptr		*new_meta[3];
	struct assoc_array_ptr		*excised_meta[1];
	struct assoc_array_ptr		*excised_subtree;
	struct assoc_array_ptr		**set_backpointers[ASSOC_ARRAY_FAN_OUT];
	struct assoc_array_ptr		*set_backpointers_to;
	struct assoc_array_node		*adjust_count_on;
	long				adjust_count_by;
	struct {
		struct assoc_array_ptr	**ptr;
		struct assoc_array_ptr	*to;
	} set[2];
	struct {
		u8			*p;
		u8			to;
	} set_parent_slot[1];
	u8				segment_cache[ASSOC_ARRAY_FAN_OUT + 1];
};

/*
 * Internal tree member pointers are marked in the bottom one or two bits to
 * indicate what type they are so that we don't have to look behind every
 * pointer to see what it points to.
 *
 * We provide functions to test type annotations and to create and translate
 * the annotated pointers.
 */
#define ASSOC_ARRAY_PTR_TYPE_MASK 0x1UL
#define ASSOC_ARRAY_PTR_LEAF_TYPE 0x0UL	/* Points to leaf (or nowhere) */
#define ASSOC_ARRAY_PTR_META_TYPE 0x1UL	/* Points to node or shortcut */
#define ASSOC_ARRAY_PTR_SUBTYPE_MASK	0x2UL
#define ASSOC_ARRAY_PTR_NODE_SUBTYPE	0x0UL
#define ASSOC_ARRAY_PTR_SHORTCUT_SUBTYPE 0x2UL

static inline bool assoc_array_ptr_is_meta(const struct assoc_array_ptr *x)
{
	return (unsigned long)x & ASSOC_ARRAY_PTR_TYPE_MASK;
}
static inline bool assoc_array_ptr_is_leaf(const struct assoc_array_ptr *x)
{
	return !assoc_array_ptr_is_meta(x);
}
static inline bool assoc_array_ptr_is_shortcut(const struct assoc_array_ptr *x)
{
	return (unsigned long)x & ASSOC_ARRAY_PTR_SUBTYPE_MASK;
}
static inline bool assoc_array_ptr_is_node(const struct assoc_array_ptr *x)
{
	return !assoc_array_ptr_is_shortcut(x);
}

static inline void *assoc_array_ptr_to_leaf(const struct assoc_array_ptr *x)
{
	return (void *)((unsigned long)x & ~ASSOC_ARRAY_PTR_TYPE_MASK);
}

static inline
unsigned long __assoc_array_ptr_to_meta(const struct assoc_array_ptr *x)
{
	return (unsigned long)x &
		~(ASSOC_ARRAY_PTR_SUBTYPE_MASK | ASSOC_ARRAY_PTR_TYPE_MASK);
}
static inline
struct assoc_array_node *assoc_array_ptr_to_node(const struct assoc_array_ptr *x)
{
	return (struct assoc_array_node *)__assoc_array_ptr_to_meta(x);
}
static inline
struct assoc_array_shortcut *assoc_array_ptr_to_shortcut(const struct assoc_array_ptr *x)
{
	return (struct assoc_array_shortcut *)__assoc_array_ptr_to_meta(x);
}

static inline
struct assoc_array_ptr *__assoc_array_x_to_ptr(const void *p, unsigned long t)
{
	return (struct assoc_array_ptr *)((unsigned long)p | t);
}
static inline
struct assoc_array_ptr *assoc_array_leaf_to_ptr(const void *p)
{
	return __assoc_array_x_to_ptr(p, ASSOC_ARRAY_PTR_LEAF_TYPE);
}
static inline
struct assoc_array_ptr *assoc_array_node_to_ptr(const struct assoc_array_node *p)
{
	return __assoc_array_x_to_ptr(
		p, ASSOC_ARRAY_PTR_META_TYPE | ASSOC_ARRAY_PTR_NODE_SUBTYPE);
}
static inline
struct assoc_array_ptr *assoc_array_shortcut_to_ptr(const struct assoc_array_shortcut *p)
{
	return __assoc_array_x_to_ptr(
		p, ASSOC_ARRAY_PTR_META_TYPE | ASSOC_ARRAY_PTR_SHORTCUT_SUBTYPE);
}

#endif /* CONFIG_ASSOCIATIVE_ARRAY */
#endif /* _LINUX_ASSOC_ARRAY_PRIV_H */