#include <linux/err.h>
#include <linux/gfp.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/hardirq.h>
#include "extent_map.h"


static struct kmem_cache *extent_map_cache;

int __init extent_map_init(void)
{
        extent_map_cache = kmem_cache_create("extent_map",
                        sizeof(struct extent_map), 0,
                        SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD, NULL);
        if (!extent_map_cache)
                return -ENOMEM;
        return 0;
}

void extent_map_exit(void)
{
        if (extent_map_cache)
                kmem_cache_destroy(extent_map_cache);
}

/**
 * extent_map_tree_init - initialize extent map tree
 * @tree:               tree to initialize
 * @mask:               flags for memory allocations during tree operations
 *
 * Initialize the extent tree @tree.  Should be called for each new inode
 * or other user of the extent_map interface.
 */
void extent_map_tree_init(struct extent_map_tree *tree, gfp_t mask)
{
        tree->map.rb_node = NULL;
        rwlock_init(&tree->lock);
}

/**
 * alloc_extent_map - allocate new extent map structure
 * @mask:       memory allocation flags
 *
 * Allocate a new extent_map structure.  The new structure is
 * returned with a reference count of one and needs to be
 * freed using free_extent_map()
 */
struct extent_map *alloc_extent_map(gfp_t mask)
{
        struct extent_map *em;
        em = kmem_cache_alloc(extent_map_cache, mask);
        if (!em || IS_ERR(em))
                return em;
        em->in_tree = 0;
        em->flags = 0;
        atomic_set(&em->refs, 1);
        return em;
}

/**
 * free_extent_map - drop reference count of an extent_map
 * @em:         extent map beeing releasead
 *
 * Drops the reference out on @em by one and free the structure
 * if the reference count hits zero.
 */
void free_extent_map(struct extent_map *em)
{
        if (!em)
                return;
        WARN_ON(atomic_read(&em->refs) == 0);
        if (atomic_dec_and_test(&em->refs)) {
                WARN_ON(em->in_tree);
                kmem_cache_free(extent_map_cache, em);
        }
}

static struct rb_node *tree_insert(struct rb_root *root, u64 offset,
                                   struct rb_node *node)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        struct extent_map *entry;

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct extent_map, rb_node);

                WARN_ON(!entry->in_tree);

                if (offset < entry->start)
                        p = &(*p)->rb_left;
                else if (offset >= extent_map_end(entry))
                        p = &(*p)->rb_right;
                else
                        return parent;
        }

        entry = rb_entry(node, struct extent_map, rb_node);
        entry->in_tree = 1;
        rb_link_node(node, parent, p);
        rb_insert_color(node, root);
        return NULL;
}

/*
 * search through the tree for an extent_map with a given offset.  If
 * it can't be found, try to find some neighboring extents
 */
static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
                                     struct rb_node **prev_ret,
                                     struct rb_node **next_ret)
{
        struct rb_node *n = root->rb_node;
        struct rb_node *prev = NULL;
        struct rb_node *orig_prev = NULL;
        struct extent_map *entry;
        struct extent_map *prev_entry = NULL;

        while (n) {
                entry = rb_entry(n, struct extent_map, rb_node);
                prev = n;
                prev_entry = entry;

                WARN_ON(!entry->in_tree);

                if (offset < entry->start)
                        n = n->rb_left;
                else if (offset >= extent_map_end(entry))
                        n = n->rb_right;
                else
                        return n;
        }

        if (prev_ret) {
                orig_prev = prev;
                while (prev && offset >= extent_map_end(prev_entry)) {
                        prev = rb_next(prev);
                        prev_entry = rb_entry(prev, struct extent_map, rb_node);
                }
                *prev_ret = prev;
                prev = orig_prev;
        }

        if (next_ret) {
                prev_entry = rb_entry(prev, struct extent_map, rb_node);
                while (prev && offset < prev_entry->start) {
                        prev = rb_prev(prev);
                        prev_entry = rb_entry(prev, struct extent_map, rb_node);
                }
                *next_ret = prev;
        }
        return NULL;
}

/*
 * look for an offset in the tree, and if it can't be found, return
 * the first offset we can find smaller than 'offset'.
 */
static inline struct rb_node *tree_search(struct rb_root *root, u64 offset)
{
        struct rb_node *prev;
        struct rb_node *ret;
        ret = __tree_search(root, offset, &prev, NULL);
        if (!ret)
                return prev;
        return ret;
}

/* check to see if two extent_map structs are adjacent and safe to merge */
static int mergable_maps(struct extent_map *prev, struct extent_map *next)
{
        if (test_bit(EXTENT_FLAG_PINNED, &prev->flags))
                return 0;

        /*
         * don't merge compressed extents, we need to know their
         * actual size
         */
        if (test_bit(EXTENT_FLAG_COMPRESSED, &prev->flags))
                return 0;

        if (extent_map_end(prev) == next->start &&
            prev->flags == next->flags &&
            prev->bdev == next->bdev &&
            ((next->block_start == EXTENT_MAP_HOLE &&
              prev->block_start == EXTENT_MAP_HOLE) ||
             (next->block_start == EXTENT_MAP_INLINE &&
              prev->block_start == EXTENT_MAP_INLINE) ||
             (next->block_start == EXTENT_MAP_DELALLOC &&
              prev->block_start == EXTENT_MAP_DELALLOC) ||
             (next->block_start < EXTENT_MAP_LAST_BYTE - 1 &&
              next->block_start == extent_map_block_end(prev)))) {
                return 1;
        }
        return 0;
}

int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len)
{
        int ret = 0;
        struct extent_map *merge = NULL;
        struct rb_node *rb;
        struct extent_map *em;

        write_lock(&tree->lock);
        em = lookup_extent_mapping(tree, start, len);

        WARN_ON(!em || em->start != start);

        if (!em)
                goto out;

        clear_bit(EXTENT_FLAG_PINNED, &em->flags);

        if (em->start != 0) {
                rb = rb_prev(&em->rb_node);
                if (rb)
                        merge = rb_entry(rb, struct extent_map, rb_node);
                if (rb && mergable_maps(merge, em)) {
                        em->start = merge->start;
                        em->len += merge->len;
                        em->block_len += merge->block_len;
                        em->block_start = merge->block_start;
                        merge->in_tree = 0;
                        rb_erase(&merge->rb_node, &tree->map);
                        free_extent_map(merge);
                }
        }

        rb = rb_next(&em->rb_node);
        if (rb)
                merge = rb_entry(rb, struct extent_map, rb_node);
        if (rb && mergable_maps(em, merge)) {
                em->len += merge->len;
                em->block_len += merge->len;
                rb_erase(&merge->rb_node, &tree->map);
                merge->in_tree = 0;
                free_extent_map(merge);
        }

        free_extent_map(em);
out:
        write_unlock(&tree->lock);
        return ret;

}

/**
 * add_extent_mapping - add new extent map to the extent tree
 * @tree:       tree to insert new map in
 * @em:         map to insert
 *
 * Insert @em into @tree or perform a simple forward/backward merge with
 * existing mappings.  The extent_map struct passed in will be inserted
 * into the tree directly, with an additional reference taken, or a
 * reference dropped if the merge attempt was sucessfull.
 */
int add_extent_mapping(struct extent_map_tree *tree,
                       struct extent_map *em)
{
        int ret = 0;
        struct extent_map *merge = NULL;
        struct rb_node *rb;
        struct extent_map *exist;

        exist = lookup_extent_mapping(tree, em->start, em->len);
        if (exist) {
                free_extent_map(exist);
                ret = -EEXIST;
                goto out;
        }
        rb = tree_insert(&tree->map, em->start, &em->rb_node);
        if (rb) {
                ret = -EEXIST;
                goto out;
        }
        atomic_inc(&em->refs);
        if (em->start != 0) {
                rb = rb_prev(&em->rb_node);
                if (rb)
                        merge = rb_entry(rb, struct extent_map, rb_node);
                if (rb && mergable_maps(merge, em)) {
                        em->start = merge->start;
                        em->len += merge->len;
                        em->block_len += merge->block_len;
                        em->block_start = merge->block_start;
                        merge->in_tree = 0;
                        rb_erase(&merge->rb_node, &tree->map);
                        free_extent_map(merge);
                }
         }
        rb = rb_next(&em->rb_node);
        if (rb)
                merge = rb_entry(rb, struct extent_map, rb_node);
        if (rb && mergable_maps(em, merge)) {
                em->len += merge->len;
                em->block_len += merge->len;
                rb_erase(&merge->rb_node, &tree->map);
                merge->in_tree = 0;
                free_extent_map(merge);
        }
out:
        return ret;
}

/* simple helper to do math around the end of an extent, handling wrap */
static u64 range_end(u64 start, u64 len)
{
        if (start + len < start)
                return (u64)-1;
        return start + len;
}

/**
 * lookup_extent_mapping - lookup extent_map
 * @tree:       tree to lookup in
 * @start:      byte offset to start the search
 * @len:        length of the lookup range
 *
 * Find and return the first extent_map struct in @tree that intersects the
 * [start, len] range.  There may be additional objects in the tree that
 * intersect, so check the object returned carefully to make sure that no
 * additional lookups are needed.
 */
struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
                                         u64 start, u64 len)
{
        struct extent_map *em;
        struct rb_node *rb_node;
        struct rb_node *prev = NULL;
        struct rb_node *next = NULL;
        u64 end = range_end(start, len);

        rb_node = __tree_search(&tree->map, start, &prev, &next);
        if (!rb_node && prev) {
                em = rb_entry(prev, struct extent_map, rb_node);
                if (end > em->start && start < extent_map_end(em))
                        goto found;
        }
        if (!rb_node && next) {
                em = rb_entry(next, struct extent_map, rb_node);
                if (end > em->start && start < extent_map_end(em))
                        goto found;
        }
        if (!rb_node) {
                em = NULL;
                goto out;
        }
        if (IS_ERR(rb_node)) {
                em = ERR_PTR(PTR_ERR(rb_node));
                goto out;
        }
        em = rb_entry(rb_node, struct extent_map, rb_node);
        if (end > em->start && start < extent_map_end(em))
                goto found;

        em = NULL;
        goto out;

found:
        atomic_inc(&em->refs);
out:
        return em;
}

/**
 * search_extent_mapping - find a nearby extent map
 * @tree:       tree to lookup in
 * @start:      byte offset to start the search
 * @len:        length of the lookup range
 *
 * Find and return the first extent_map struct in @tree that intersects the
 * [start, len] range.
 *
 * If one can't be found, any nearby extent may be returned
 */
struct extent_map *search_extent_mapping(struct extent_map_tree *tree,
                                         u64 start, u64 len)
{
        struct extent_map *em;
        struct rb_node *rb_node;
        struct rb_node *prev = NULL;
        struct rb_node *next = NULL;

        rb_node = __tree_search(&tree->map, start, &prev, &next);
        if (!rb_node && prev) {
                em = rb_entry(prev, struct extent_map, rb_node);
                goto found;
        }
        if (!rb_node && next) {
                em = rb_entry(next, struct extent_map, rb_node);
                goto found;
        }
        if (!rb_node) {
                em = NULL;
                goto out;
        }
        if (IS_ERR(rb_node)) {
                em = ERR_PTR(PTR_ERR(rb_node));
                goto out;
        }
        em = rb_entry(rb_node, struct extent_map, rb_node);
        goto found;

        em = NULL;
        goto out;

found:
        atomic_inc(&em->refs);
out:
        return em;
}

/**
 * remove_extent_mapping - removes an extent_map from the extent tree
 * @tree:       extent tree to remove from
 * @em:         extent map beeing removed
 *
 * Removes @em from @tree.  No reference counts are dropped, and no checks
 * are done to see if the range is in use
 */
int remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em)
{
        int ret = 0;

        WARN_ON(test_bit(EXTENT_FLAG_PINNED, &em->flags));
        rb_erase(&em->rb_node, &tree->map);
        em->in_tree = 0;
        return ret;
}