#ifndef _LINUX_GENERIC_RADIX_TREE_H
#define _LINUX_GENERIC_RADIX_TREE_H

/**
 * DOC: Generic radix trees/sparse arrays
 *
 * Very simple and minimalistic, supporting arbitrary size entries up to
 * GENRADIX_NODE_SIZE.
 *
 * A genradix is defined with the type it will store, like so:
 *
 * static GENRADIX(struct foo) foo_genradix;
 *
 * The main operations are:
 *
 * - genradix_init(radix) - initialize an empty genradix
 *
 * - genradix_free(radix) - free all memory owned by the genradix and
 *   reinitialize it
 *
 * - genradix_ptr(radix, idx) - gets a pointer to the entry at idx, returning
 *   NULL if that entry does not exist
 *
 * - genradix_ptr_alloc(radix, idx, gfp) - gets a pointer to an entry,
 *   allocating it if necessary
 *
 * - genradix_for_each(radix, iter, p) - iterate over each entry in a genradix
 *
 * The radix tree allocates one page of entries at a time, so entries may exist
 * that were never explicitly allocated - they will be initialized to all
 * zeroes.
 *
 * Internally, a genradix is just a radix tree of pages, and indexing works in
 * terms of byte offsets. The wrappers in this header file use sizeof on the
 * type the radix contains to calculate a byte offset from the index - see
 * __idx_to_offset.
 */

#include <asm/page.h>
#include <linux/bug.h>
#include <linux/limits.h>
#include <linux/log2.h>
#include <linux/math.h>
#include <linux/slab.h>
#include <linux/types.h>

struct genradix_root;

#define GENRADIX_NODE_SHIFT     9
#define GENRADIX_NODE_SIZE      (1U << GENRADIX_NODE_SHIFT)

#define GENRADIX_ARY            (GENRADIX_NODE_SIZE / sizeof(struct genradix_node *))
#define GENRADIX_ARY_SHIFT      ilog2(GENRADIX_ARY)

/* depth that's needed for a genradix that can address up to ULONG_MAX: */
#define GENRADIX_MAX_DEPTH      \
        DIV_ROUND_UP(BITS_PER_LONG - GENRADIX_NODE_SHIFT, GENRADIX_ARY_SHIFT)

#define GENRADIX_DEPTH_MASK                             \
        ((unsigned long) (roundup_pow_of_two(GENRADIX_MAX_DEPTH + 1) - 1))

static inline int genradix_depth_shift(unsigned depth)
{
        return GENRADIX_NODE_SHIFT + GENRADIX_ARY_SHIFT * depth;
}

/*
 * Returns size (of data, in bytes) that a tree of a given depth holds:
 */
static inline size_t genradix_depth_size(unsigned depth)
{
        return 1UL << genradix_depth_shift(depth);
}

static inline unsigned genradix_root_to_depth(struct genradix_root *r)
{
        return (unsigned long) r & GENRADIX_DEPTH_MASK;
}

static inline struct genradix_node *genradix_root_to_node(struct genradix_root *r)
{
        return (void *) ((unsigned long) r & ~GENRADIX_DEPTH_MASK);
}

struct __genradix {
        struct genradix_root            *root;
};

struct genradix_node {
        union {
                /* Interior node: */
                struct genradix_node    *children[GENRADIX_ARY];

                /* Leaf: */
                u8                      data[GENRADIX_NODE_SIZE];
        };
};

static inline struct genradix_node *genradix_alloc_node(gfp_t gfp_mask)
{
        return kzalloc(GENRADIX_NODE_SIZE, gfp_mask);
}

static inline void genradix_free_node(struct genradix_node *node)
{
        kfree(node);
}

/*
 * NOTE: currently, sizeof(_type) must not be larger than GENRADIX_NODE_SIZE:
 */

#define __GENRADIX_INITIALIZER                                  \
        {                                                       \
                .tree = {                                       \
                        .root = NULL,                           \
                }                                               \
        }

/*
 * We use a 0 size array to stash the type we're storing without taking any
 * space at runtime - then the various accessor macros can use typeof() to get
 * to it for casts/sizeof - we also force the alignment so that storing a type
 * with a ridiculous alignment doesn't blow up the alignment or size of the
 * genradix.
 */

#define GENRADIX(_type)                                         \
struct {                                                        \
        struct __genradix       tree;                           \
        _type                   type[0] __aligned(1);           \
}

#define DEFINE_GENRADIX(_name, _type)                           \
        GENRADIX(_type) _name = __GENRADIX_INITIALIZER

/**
 * genradix_init - initialize a genradix
 * @_radix:     genradix to initialize
 *
 * Does not fail
 */
#define genradix_init(_radix)                                   \
do {                                                            \
        *(_radix) = (typeof(*_radix)) __GENRADIX_INITIALIZER;   \
} while (0)

void __genradix_free(struct __genradix *);

/**
 * genradix_free: free all memory owned by a genradix
 * @_radix: the genradix to free
 *
 * After freeing, @_radix will be reinitialized and empty
 */
#define genradix_free(_radix)   __genradix_free(&(_radix)->tree)

static inline size_t __idx_to_offset(size_t idx, size_t obj_size)
{
        if (__builtin_constant_p(obj_size))
                BUILD_BUG_ON(obj_size > GENRADIX_NODE_SIZE);
        else
                BUG_ON(obj_size > GENRADIX_NODE_SIZE);

        if (!is_power_of_2(obj_size)) {
                size_t objs_per_page = GENRADIX_NODE_SIZE / obj_size;

                return (idx / objs_per_page) * GENRADIX_NODE_SIZE +
                        (idx % objs_per_page) * obj_size;
        } else {
                return idx * obj_size;
        }
}

#define __genradix_cast(_radix)         (typeof((_radix)->type[0]) *)
#define __genradix_obj_size(_radix)     sizeof((_radix)->type[0])
#define __genradix_objs_per_page(_radix)                        \
        (GENRADIX_NODE_SIZE / sizeof((_radix)->type[0]))
#define __genradix_page_remainder(_radix)                       \
        (GENRADIX_NODE_SIZE % sizeof((_radix)->type[0]))

#define __genradix_idx_to_offset(_radix, _idx)                  \
        __idx_to_offset(_idx, __genradix_obj_size(_radix))

static inline void *__genradix_ptr_inlined(struct __genradix *radix, size_t offset)
{
        struct genradix_root *r = READ_ONCE(radix->root);
        struct genradix_node *n = genradix_root_to_node(r);
        unsigned level          = genradix_root_to_depth(r);
        unsigned shift          = genradix_depth_shift(level);

        if (unlikely(ilog2(offset) >= genradix_depth_shift(level)))
                return NULL;

        while (n && shift > GENRADIX_NODE_SHIFT) {
                shift -= GENRADIX_ARY_SHIFT;
                n = n->children[offset >> shift];
                offset &= (1UL << shift) - 1;
        }

        return n ? &n->data[offset] : NULL;
}

#define genradix_ptr_inlined(_radix, _idx)                      \
        (__genradix_cast(_radix)                                \
         __genradix_ptr_inlined(&(_radix)->tree,                \
                        __genradix_idx_to_offset(_radix, _idx)))

void *__genradix_ptr(struct __genradix *, size_t);

/**
 * genradix_ptr - get a pointer to a genradix entry
 * @_radix:     genradix to access
 * @_idx:       index to fetch
 *
 * Returns a pointer to entry at @_idx, or NULL if that entry does not exist.
 */
#define genradix_ptr(_radix, _idx)                              \
        (__genradix_cast(_radix)                                \
         __genradix_ptr(&(_radix)->tree,                        \
                        __genradix_idx_to_offset(_radix, _idx)))

void *__genradix_ptr_alloc(struct __genradix *, size_t,
                           struct genradix_node **, gfp_t);

#define genradix_ptr_alloc_inlined(_radix, _idx, _gfp)                  \
        (__genradix_cast(_radix)                                        \
         (__genradix_ptr_inlined(&(_radix)->tree,                       \
                        __genradix_idx_to_offset(_radix, _idx)) ?:      \
          __genradix_ptr_alloc(&(_radix)->tree,                         \
                        __genradix_idx_to_offset(_radix, _idx),         \
                        NULL, _gfp)))

#define genradix_ptr_alloc_preallocated_inlined(_radix, _idx, _new_node, _gfp)\
        (__genradix_cast(_radix)                                        \
         (__genradix_ptr_inlined(&(_radix)->tree,                       \
                        __genradix_idx_to_offset(_radix, _idx)) ?:      \
          __genradix_ptr_alloc(&(_radix)->tree,                         \
                        __genradix_idx_to_offset(_radix, _idx),         \
                        _new_node, _gfp)))

/**
 * genradix_ptr_alloc - get a pointer to a genradix entry, allocating it
 *                      if necessary
 * @_radix:     genradix to access
 * @_idx:       index to fetch
 * @_gfp:       gfp mask
 *
 * Returns a pointer to entry at @_idx, or NULL on allocation failure
 */
#define genradix_ptr_alloc(_radix, _idx, _gfp)                  \
        (__genradix_cast(_radix)                                \
         __genradix_ptr_alloc(&(_radix)->tree,                  \
                        __genradix_idx_to_offset(_radix, _idx), \
                        NULL, _gfp))

#define genradix_ptr_alloc_preallocated(_radix, _idx, _new_node, _gfp)\
        (__genradix_cast(_radix)                                \
         __genradix_ptr_alloc(&(_radix)->tree,                  \
                        __genradix_idx_to_offset(_radix, _idx), \
                        _new_node, _gfp))

struct genradix_iter {
        size_t                  offset;
        size_t                  pos;
};

/**
 * genradix_iter_init - initialize a genradix_iter
 * @_radix:     genradix that will be iterated over
 * @_idx:       index to start iterating from
 */
#define genradix_iter_init(_radix, _idx)                        \
        ((struct genradix_iter) {                               \
                .pos    = (_idx),                               \
                .offset = __genradix_idx_to_offset((_radix), (_idx)),\
        })

void *__genradix_iter_peek(struct genradix_iter *, struct __genradix *, size_t);

/**
 * genradix_iter_peek - get first entry at or above iterator's current
 *                      position
 * @_iter:      a genradix_iter
 * @_radix:     genradix being iterated over
 *
 * If no more entries exist at or above @_iter's current position, returns NULL
 */
#define genradix_iter_peek(_iter, _radix)                       \
        (__genradix_cast(_radix)                                \
         __genradix_iter_peek(_iter, &(_radix)->tree,           \
                        __genradix_objs_per_page(_radix)))

void *__genradix_iter_peek_prev(struct genradix_iter *, struct __genradix *,
                                size_t, size_t);

/**
 * genradix_iter_peek_prev - get first entry at or below iterator's current
 *                           position
 * @_iter:      a genradix_iter
 * @_radix:     genradix being iterated over
 *
 * If no more entries exist at or below @_iter's current position, returns NULL
 */
#define genradix_iter_peek_prev(_iter, _radix)                  \
        (__genradix_cast(_radix)                                \
         __genradix_iter_peek_prev(_iter, &(_radix)->tree,      \
                        __genradix_objs_per_page(_radix),       \
                        __genradix_obj_size(_radix) +           \
                        __genradix_page_remainder(_radix)))

static inline void __genradix_iter_advance(struct genradix_iter *iter,
                                           size_t obj_size)
{
        if (iter->offset + obj_size < iter->offset) {
                iter->offset    = SIZE_MAX;
                iter->pos       = SIZE_MAX;
                return;
        }

        iter->offset += obj_size;

        if (!is_power_of_2(obj_size) &&
            (iter->offset & (GENRADIX_NODE_SIZE - 1)) + obj_size > GENRADIX_NODE_SIZE)
                iter->offset = round_up(iter->offset, GENRADIX_NODE_SIZE);

        iter->pos++;
}

#define genradix_iter_advance(_iter, _radix)                    \
        __genradix_iter_advance(_iter, __genradix_obj_size(_radix))

static inline void __genradix_iter_rewind(struct genradix_iter *iter,
                                          size_t obj_size)
{
        if (iter->offset == 0 ||
            iter->offset == SIZE_MAX) {
                iter->offset = SIZE_MAX;
                return;
        }

        if ((iter->offset & (GENRADIX_NODE_SIZE - 1)) == 0)
                iter->offset -= GENRADIX_NODE_SIZE % obj_size;

        iter->offset -= obj_size;
        iter->pos--;
}

#define genradix_iter_rewind(_iter, _radix)                     \
        __genradix_iter_rewind(_iter, __genradix_obj_size(_radix))

#define genradix_for_each_from(_radix, _iter, _p, _start)       \
        for (_iter = genradix_iter_init(_radix, _start);        \
             (_p = genradix_iter_peek(&_iter, _radix)) != NULL; \
             genradix_iter_advance(&_iter, _radix))

/**
 * genradix_for_each - iterate over entry in a genradix
 * @_radix:     genradix to iterate over
 * @_iter:      a genradix_iter to track current position
 * @_p:         pointer to genradix entry type
 *
 * On every iteration, @_p will point to the current entry, and @_iter.pos
 * will be the current entry's index.
 */
#define genradix_for_each(_radix, _iter, _p)                    \
        genradix_for_each_from(_radix, _iter, _p, 0)

#define genradix_last_pos(_radix)                               \
        (SIZE_MAX / GENRADIX_NODE_SIZE * __genradix_objs_per_page(_radix) - 1)

/**
 * genradix_for_each_reverse - iterate over entry in a genradix, reverse order
 * @_radix:     genradix to iterate over
 * @_iter:      a genradix_iter to track current position
 * @_p:         pointer to genradix entry type
 *
 * On every iteration, @_p will point to the current entry, and @_iter.pos
 * will be the current entry's index.
 */
#define genradix_for_each_reverse(_radix, _iter, _p)            \
        for (_iter = genradix_iter_init(_radix, genradix_last_pos(_radix));\
             (_p = genradix_iter_peek_prev(&_iter, _radix)) != NULL;\
             genradix_iter_rewind(&_iter, _radix))

int __genradix_prealloc(struct __genradix *, size_t, gfp_t);

/**
 * genradix_prealloc - preallocate entries in a generic radix tree
 * @_radix:     genradix to preallocate
 * @_nr:        number of entries to preallocate
 * @_gfp:       gfp mask
 *
 * Returns 0 on success, -ENOMEM on failure
 */
#define genradix_prealloc(_radix, _nr, _gfp)                    \
         __genradix_prealloc(&(_radix)->tree,                   \
                        __genradix_idx_to_offset(_radix, _nr + 1),\
                        _gfp)


#endif /* _LINUX_GENERIC_RADIX_TREE_H */