/*
 * Copyright (C) 2011 STRATO AG
 * written by Arne Jansen <sensille@gmx.net>
 * Distributed under the GNU GPL license version 2.
 */

#include <linux/slab.h>
#include <linux/export.h>
#include "ulist.h"

/*
 * ulist is a generic data structure to hold a collection of unique u64
 * values. The only operations it supports is adding to the list and
 * enumerating it.
 * It is possible to store an auxiliary value along with the key.
 *
 * The implementation is preliminary and can probably be sped up
 * significantly. A first step would be to store the values in an rbtree
 * as soon as ULIST_SIZE is exceeded.
 *
 * A sample usage for ulists is the enumeration of directed graphs without
 * visiting a node twice. The pseudo-code could look like this:
 *
 * ulist = ulist_alloc();
 * ulist_add(ulist, root);
 * ULIST_ITER_INIT(&uiter);
 *
 * while ((elem = ulist_next(ulist, &uiter)) {
 *      for (all child nodes n in elem)
 *              ulist_add(ulist, n);
 *      do something useful with the node;
 * }
 * ulist_free(ulist);
 *
 * This assumes the graph nodes are adressable by u64. This stems from the
 * usage for tree enumeration in btrfs, where the logical addresses are
 * 64 bit.
 *
 * It is also useful for tree enumeration which could be done elegantly
 * recursively, but is not possible due to kernel stack limitations. The
 * loop would be similar to the above.
 */

/**
 * ulist_init - freshly initialize a ulist
 * @ulist:      the ulist to initialize
 *
 * Note: don't use this function to init an already used ulist, use
 * ulist_reinit instead.
 */
void ulist_init(struct ulist *ulist)
{
        ulist->nnodes = 0;
        ulist->nodes = ulist->int_nodes;
        ulist->nodes_alloced = ULIST_SIZE;
        ulist->root = RB_ROOT;
}
EXPORT_SYMBOL(ulist_init);

/**
 * ulist_fini - free up additionally allocated memory for the ulist
 * @ulist:      the ulist from which to free the additional memory
 *
 * This is useful in cases where the base 'struct ulist' has been statically
 * allocated.
 */
void ulist_fini(struct ulist *ulist)
{
        /*
         * The first ULIST_SIZE elements are stored inline in struct ulist.
         * Only if more elements are alocated they need to be freed.
         */
        if (ulist->nodes_alloced > ULIST_SIZE)
                kfree(ulist->nodes);
        ulist->nodes_alloced = 0;       /* in case ulist_fini is called twice */
        ulist->root = RB_ROOT;
}
EXPORT_SYMBOL(ulist_fini);

/**
 * ulist_reinit - prepare a ulist for reuse
 * @ulist:      ulist to be reused
 *
 * Free up all additional memory allocated for the list elements and reinit
 * the ulist.
 */
void ulist_reinit(struct ulist *ulist)
{
        ulist_fini(ulist);
        ulist_init(ulist);
}
EXPORT_SYMBOL(ulist_reinit);

/**
 * ulist_alloc - dynamically allocate a ulist
 * @gfp_mask:   allocation flags to for base allocation
 *
 * The allocated ulist will be returned in an initialized state.
 */
struct ulist *ulist_alloc(gfp_t gfp_mask)
{
        struct ulist *ulist = kmalloc(sizeof(*ulist), gfp_mask);

        if (!ulist)
                return NULL;

        ulist_init(ulist);

        return ulist;
}
EXPORT_SYMBOL(ulist_alloc);

/**
 * ulist_free - free dynamically allocated ulist
 * @ulist:      ulist to free
 *
 * It is not necessary to call ulist_fini before.
 */
void ulist_free(struct ulist *ulist)
{
        if (!ulist)
                return;
        ulist_fini(ulist);
        kfree(ulist);
}
EXPORT_SYMBOL(ulist_free);

static struct ulist_node *ulist_rbtree_search(struct ulist *ulist, u64 val)
{
        struct rb_node *n = ulist->root.rb_node;
        struct ulist_node *u = NULL;

        while (n) {
                u = rb_entry(n, struct ulist_node, rb_node);
                if (u->val < val)
                        n = n->rb_right;
                else if (u->val > val)
                        n = n->rb_left;
                else
                        return u;
        }
        return NULL;
}

static int ulist_rbtree_insert(struct ulist *ulist, struct ulist_node *ins)
{
        struct rb_node **p = &ulist->root.rb_node;
        struct rb_node *parent = NULL;
        struct ulist_node *cur = NULL;

        while (*p) {
                parent = *p;
                cur = rb_entry(parent, struct ulist_node, rb_node);

                if (cur->val < ins->val)
                        p = &(*p)->rb_right;
                else if (cur->val > ins->val)
                        p = &(*p)->rb_left;
                else
                        return -EEXIST;
        }
        rb_link_node(&ins->rb_node, parent, p);
        rb_insert_color(&ins->rb_node, &ulist->root);
        return 0;
}

/**
 * ulist_add - add an element to the ulist
 * @ulist:      ulist to add the element to
 * @val:        value to add to ulist
 * @aux:        auxiliary value to store along with val
 * @gfp_mask:   flags to use for allocation
 *
 * Note: locking must be provided by the caller. In case of rwlocks write
 *       locking is needed
 *
 * Add an element to a ulist. The @val will only be added if it doesn't
 * already exist. If it is added, the auxiliary value @aux is stored along with
 * it. In case @val already exists in the ulist, @aux is ignored, even if
 * it differs from the already stored value.
 *
 * ulist_add returns 0 if @val already exists in ulist and 1 if @val has been
 * inserted.
 * In case of allocation failure -ENOMEM is returned and the ulist stays
 * unaltered.
 */
int ulist_add(struct ulist *ulist, u64 val, u64 aux, gfp_t gfp_mask)
{
        return ulist_add_merge(ulist, val, aux, NULL, gfp_mask);
}

int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux,
                    u64 *old_aux, gfp_t gfp_mask)
{
        int ret = 0;
        struct ulist_node *node = NULL;
        node = ulist_rbtree_search(ulist, val);
        if (node) {
                if (old_aux)
                        *old_aux = node->aux;
                return 0;
        }

        if (ulist->nnodes >= ulist->nodes_alloced) {
                u64 new_alloced = ulist->nodes_alloced + 128;
                struct ulist_node *new_nodes;
                void *old = NULL;

                /*
                 * if nodes_alloced == ULIST_SIZE no memory has been allocated
                 * yet, so pass NULL to krealloc
                 */
                if (ulist->nodes_alloced > ULIST_SIZE)
                        old = ulist->nodes;

                new_nodes = krealloc(old, sizeof(*new_nodes) * new_alloced,
                                     gfp_mask);
                if (!new_nodes)
                        return -ENOMEM;

                if (!old)
                        memcpy(new_nodes, ulist->int_nodes,
                               sizeof(ulist->int_nodes));

                ulist->nodes = new_nodes;
                ulist->nodes_alloced = new_alloced;
        }
        ulist->nodes[ulist->nnodes].val = val;
        ulist->nodes[ulist->nnodes].aux = aux;
        ret = ulist_rbtree_insert(ulist, &ulist->nodes[ulist->nnodes]);
        BUG_ON(ret);
        ++ulist->nnodes;

        return 1;
}
EXPORT_SYMBOL(ulist_add);

/**
 * ulist_next - iterate ulist
 * @ulist:      ulist to iterate
 * @uiter:      iterator variable, initialized with ULIST_ITER_INIT(&iterator)
 *
 * Note: locking must be provided by the caller. In case of rwlocks only read
 *       locking is needed
 *
 * This function is used to iterate an ulist.
 * It returns the next element from the ulist or %NULL when the
 * end is reached. No guarantee is made with respect to the order in which
 * the elements are returned. They might neither be returned in order of
 * addition nor in ascending order.
 * It is allowed to call ulist_add during an enumeration. Newly added items
 * are guaranteed to show up in the running enumeration.
 */
struct ulist_node *ulist_next(struct ulist *ulist, struct ulist_iterator *uiter)
{
        if (ulist->nnodes == 0)
                return NULL;
        if (uiter->i < 0 || uiter->i >= ulist->nnodes)
                return NULL;

        return &ulist->nodes[uiter->i++];
}
EXPORT_SYMBOL(ulist_next);