#include <linux/export.h>
#include <linux/generic-radix-tree.h>
#include <linux/gfp.h>
#include <linux/kmemleak.h>

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

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

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

static inline int genradix_depth_shift(unsigned depth)
{
        return PAGE_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);
}

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

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

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);
}

/*
 * Returns pointer to the specified byte @offset within @radix, or NULL if not
 * allocated
 */
void *__genradix_ptr(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);

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

        while (1) {
                if (!n)
                        return NULL;
                if (!level)
                        break;

                level--;

                n = n->children[offset >> genradix_depth_shift(level)];
                offset &= genradix_depth_size(level) - 1;
        }

        return &n->data[offset];
}
EXPORT_SYMBOL(__genradix_ptr);

static inline struct genradix_node *genradix_alloc_node(gfp_t gfp_mask)
{
        struct genradix_node *node;

        node = (struct genradix_node *)__get_free_page(gfp_mask|__GFP_ZERO);

        /*
         * We're using pages (not slab allocations) directly for kernel data
         * structures, so we need to explicitly inform kmemleak of them in order
         * to avoid false positive memory leak reports.
         */
        kmemleak_alloc(node, PAGE_SIZE, 1, gfp_mask);
        return node;
}

static inline void genradix_free_node(struct genradix_node *node)
{
        kmemleak_free(node);
        free_page((unsigned long)node);
}

/*
 * Returns pointer to the specified byte @offset within @radix, allocating it if
 * necessary - newly allocated slots are always zeroed out:
 */
void *__genradix_ptr_alloc(struct __genradix *radix, size_t offset,
                           gfp_t gfp_mask)
{
        struct genradix_root *v = READ_ONCE(radix->root);
        struct genradix_node *n, *new_node = NULL;
        unsigned level;

        /* Increase tree depth if necessary: */
        while (1) {
                struct genradix_root *r = v, *new_root;

                n       = genradix_root_to_node(r);
                level   = genradix_root_to_depth(r);

                if (n && ilog2(offset) < genradix_depth_shift(level))
                        break;

                if (!new_node) {
                        new_node = genradix_alloc_node(gfp_mask);
                        if (!new_node)
                                return NULL;
                }

                new_node->children[0] = n;
                new_root = ((struct genradix_root *)
                            ((unsigned long) new_node | (n ? level + 1 : 0)));

                if ((v = cmpxchg_release(&radix->root, r, new_root)) == r) {
                        v = new_root;
                        new_node = NULL;
                }
        }

        while (level--) {
                struct genradix_node **p =
                        &n->children[offset >> genradix_depth_shift(level)];
                offset &= genradix_depth_size(level) - 1;

                n = READ_ONCE(*p);
                if (!n) {
                        if (!new_node) {
                                new_node = genradix_alloc_node(gfp_mask);
                                if (!new_node)
                                        return NULL;
                        }

                        if (!(n = cmpxchg_release(p, NULL, new_node)))
                                swap(n, new_node);
                }
        }

        if (new_node)
                genradix_free_node(new_node);

        return &n->data[offset];
}
EXPORT_SYMBOL(__genradix_ptr_alloc);

void *__genradix_iter_peek(struct genradix_iter *iter,
                           struct __genradix *radix,
                           size_t objs_per_page)
{
        struct genradix_root *r;
        struct genradix_node *n;
        unsigned level, i;
restart:
        r = READ_ONCE(radix->root);
        if (!r)
                return NULL;

        n       = genradix_root_to_node(r);
        level   = genradix_root_to_depth(r);

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

        while (level) {
                level--;

                i = (iter->offset >> genradix_depth_shift(level)) &
                        (GENRADIX_ARY - 1);

                while (!n->children[i]) {
                        i++;
                        iter->offset = round_down(iter->offset +
                                           genradix_depth_size(level),
                                           genradix_depth_size(level));
                        iter->pos = (iter->offset >> PAGE_SHIFT) *
                                objs_per_page;
                        if (i == GENRADIX_ARY)
                                goto restart;
                }

                n = n->children[i];
        }

        return &n->data[iter->offset & (PAGE_SIZE - 1)];
}
EXPORT_SYMBOL(__genradix_iter_peek);

static void genradix_free_recurse(struct genradix_node *n, unsigned level)
{
        if (level) {
                unsigned i;

                for (i = 0; i < GENRADIX_ARY; i++)
                        if (n->children[i])
                                genradix_free_recurse(n->children[i], level - 1);
        }

        genradix_free_node(n);
}

int __genradix_prealloc(struct __genradix *radix, size_t size,
                        gfp_t gfp_mask)
{
        size_t offset;

        for (offset = 0; offset < size; offset += PAGE_SIZE)
                if (!__genradix_ptr_alloc(radix, offset, gfp_mask))
                        return -ENOMEM;

        return 0;
}
EXPORT_SYMBOL(__genradix_prealloc);

void __genradix_free(struct __genradix *radix)
{
        struct genradix_root *r = xchg(&radix->root, NULL);

        genradix_free_recurse(genradix_root_to_node(r),
                              genradix_root_to_depth(r));
}
EXPORT_SYMBOL(__genradix_free);