Btrfs: early reference counting

[linux-2.6] / fs / btrfs / ctree.c

#include <stdio.h>
#include <stdlib.h>
#include "kerncompat.h"
#include "radix-tree.h"
#include "ctree.h"
#include "disk-io.h"
#include "print-tree.h"

static int split_node(struct ctree_root *root, struct ctree_path *path,
                      int level);
static int split_leaf(struct ctree_root *root, struct ctree_path *path,
                      int data_size);
static int push_node_left(struct ctree_root *root, struct tree_buffer *dst,
                          struct tree_buffer *src);
static int balance_node_right(struct ctree_root *root,
                              struct tree_buffer *dst_buf,
                              struct tree_buffer *src_buf);
static int del_ptr(struct ctree_root *root, struct ctree_path *path, int level,
                   int slot);

inline void init_path(struct ctree_path *p)
{
        memset(p, 0, sizeof(*p));
}

void release_path(struct ctree_root *root, struct ctree_path *p)
{
        int i;
        for (i = 0; i < MAX_LEVEL; i++) {
                if (!p->nodes[i])
                        break;
                tree_block_release(root, p->nodes[i]);
        }
        memset(p, 0, sizeof(*p));
}

int btrfs_cow_block(struct ctree_root *root,
                    struct tree_buffer *buf,
                    struct tree_buffer *parent,
                    int parent_slot,
                    struct tree_buffer **cow_ret)
{
        struct tree_buffer *cow;

        if (!list_empty(&buf->dirty)) {
                *cow_ret = buf;
                return 0;
        }
        cow = alloc_free_block(root);
        memcpy(&cow->node, &buf->node, sizeof(buf->node));
        cow->node.header.blocknr = cow->blocknr;
        *cow_ret = cow;
        if (buf == root->node) {
                root->node = cow;
                cow->count++;
                tree_block_release(root, buf);
        } else {
                parent->node.blockptrs[parent_slot] = cow->blocknr;
                BUG_ON(list_empty(&parent->dirty));
        }
        if (0 && root != root->extent_root && !is_leaf(cow->node.header.flags)) {
                btrfs_inc_ref(root, cow);
        }
        tree_block_release(root, buf);
        return 0;
}

/*
 * The leaf data grows from end-to-front in the node.
 * this returns the address of the start of the last item,
 * which is the stop of the leaf data stack
 */
static inline unsigned int leaf_data_end(struct leaf *leaf)
{
        unsigned int nr = leaf->header.nritems;
        if (nr == 0)
                return sizeof(leaf->data);
        return leaf->items[nr-1].offset;
}

/*
 * The space between the end of the leaf items and
 * the start of the leaf data.  IOW, how much room
 * the leaf has left for both items and data
 */
int leaf_free_space(struct leaf *leaf)
{
        int data_end = leaf_data_end(leaf);
        int nritems = leaf->header.nritems;
        char *items_end = (char *)(leaf->items + nritems + 1);
        return (char *)(leaf->data + data_end) - (char *)items_end;
}

/*
 * compare two keys in a memcmp fashion
 */
int comp_keys(struct key *k1, struct key *k2)
{
        if (k1->objectid > k2->objectid)
                return 1;
        if (k1->objectid < k2->objectid)
                return -1;
        if (k1->flags > k2->flags)
                return 1;
        if (k1->flags < k2->flags)
                return -1;
        if (k1->offset > k2->offset)
                return 1;
        if (k1->offset < k2->offset)
                return -1;
        return 0;
}

int check_node(struct ctree_path *path, int level)
{
        int i;
        struct node *parent = NULL;
        struct node *node = &path->nodes[level]->node;
        int parent_slot;

        if (path->nodes[level + 1])
                parent = &path->nodes[level + 1]->node;
        parent_slot = path->slots[level + 1];
        if (parent && node->header.nritems > 0) {
                struct key *parent_key;
                parent_key = &parent->keys[parent_slot];
                BUG_ON(memcmp(parent_key, node->keys, sizeof(struct key)));
                BUG_ON(parent->blockptrs[parent_slot] != node->header.blocknr);
        }
        BUG_ON(node->header.nritems > NODEPTRS_PER_BLOCK);
        for (i = 0; i < node->header.nritems - 2; i++) {
                BUG_ON(comp_keys(&node->keys[i], &node->keys[i+1]) >= 0);
        }
        return 0;
}

int check_leaf(struct ctree_path *path, int level)
{
        int i;
        struct leaf *leaf = &path->nodes[level]->leaf;
        struct node *parent = NULL;
        int parent_slot;

        if (path->nodes[level + 1])
                parent = &path->nodes[level + 1]->node;
        parent_slot = path->slots[level + 1];
        if (parent && leaf->header.nritems > 0) {
                struct key *parent_key;
                parent_key = &parent->keys[parent_slot];
                BUG_ON(memcmp(parent_key, &leaf->items[0].key,
                       sizeof(struct key)));
                BUG_ON(parent->blockptrs[parent_slot] != leaf->header.blocknr);
        }
        for (i = 0; i < leaf->header.nritems - 2; i++) {
                BUG_ON(comp_keys(&leaf->items[i].key,
                                 &leaf->items[i+1].key) >= 0);
                BUG_ON(leaf->items[i].offset != leaf->items[i + 1].offset +
                    leaf->items[i + 1].size);
                if (i == 0) {
                        BUG_ON(leaf->items[i].offset + leaf->items[i].size !=
                                LEAF_DATA_SIZE);
                }
        }
        BUG_ON(leaf_free_space(leaf) < 0);
        return 0;
}

int check_block(struct ctree_path *path, int level)
{
        if (level == 0)
                return check_leaf(path, level);
        return check_node(path, level);
}

/*
 * search for key in the array p.  items p are item_size apart
 * and there are 'max' items in p
 * the slot in the array is returned via slot, and it points to
 * the place where you would insert key if it is not found in
 * the array.
 *
 * slot may point to max if the key is bigger than all of the keys
 */
int generic_bin_search(char *p, int item_size, struct key *key,
                       int max, int *slot)
{
        int low = 0;
        int high = max;
        int mid;
        int ret;
        struct key *tmp;

        while(low < high) {
                mid = (low + high) / 2;
                tmp = (struct key *)(p + mid * item_size);
                ret = comp_keys(tmp, key);

                if (ret < 0)
                        low = mid + 1;
                else if (ret > 0)
                        high = mid;
                else {
                        *slot = mid;
                        return 0;
                }
        }
        *slot = low;
        return 1;
}

/*
 * simple bin_search frontend that does the right thing for
 * leaves vs nodes
 */
int bin_search(struct node *c, struct key *key, int *slot)
{
        if (is_leaf(c->header.flags)) {
                struct leaf *l = (struct leaf *)c;
                return generic_bin_search((void *)l->items, sizeof(struct item),
                                          key, c->header.nritems, slot);
        } else {
                return generic_bin_search((void *)c->keys, sizeof(struct key),
                                          key, c->header.nritems, slot);
        }
        return -1;
}

struct tree_buffer *read_node_slot(struct ctree_root *root,
                                   struct tree_buffer *parent_buf,
                                   int slot)
{
        struct node *node = &parent_buf->node;
        if (slot < 0)
                return NULL;
        if (slot >= node->header.nritems)
                return NULL;
        return read_tree_block(root, node->blockptrs[slot]);
}

static int balance_level(struct ctree_root *root, struct ctree_path *path,
                        int level)
{
        struct tree_buffer *right_buf;
        struct tree_buffer *mid_buf;
        struct tree_buffer *left_buf;
        struct tree_buffer *parent_buf = NULL;
        struct node *right = NULL;
        struct node *mid;
        struct node *left = NULL;
        struct node *parent = NULL;
        int ret = 0;
        int wret;
        int pslot;
        int orig_slot = path->slots[level];
        u64 orig_ptr;

        if (level == 0)
                return 0;

        mid_buf = path->nodes[level];
        mid = &mid_buf->node;
        orig_ptr = mid->blockptrs[orig_slot];

        if (level < MAX_LEVEL - 1)
                parent_buf = path->nodes[level + 1];
        pslot = path->slots[level + 1];

        if (!parent_buf) {
                struct tree_buffer *child;
                u64 blocknr = mid_buf->blocknr;

                if (mid->header.nritems != 1)
                        return 0;

                /* promote the child to a root */
                child = read_node_slot(root, mid_buf, 0);
                BUG_ON(!child);
                root->node = child;
                path->nodes[level] = NULL;
                /* once for the path */
                tree_block_release(root, mid_buf);
                /* once for the root ptr */
                tree_block_release(root, mid_buf);
                clean_tree_block(root, mid_buf);
                return free_extent(root, blocknr, 1);
        }
        parent = &parent_buf->node;

        if (mid->header.nritems > NODEPTRS_PER_BLOCK / 4)
                return 0;

        left_buf = read_node_slot(root, parent_buf, pslot - 1);
        right_buf = read_node_slot(root, parent_buf, pslot + 1);

        /* first, try to make some room in the middle buffer */
        if (left_buf) {
                btrfs_cow_block(root, left_buf, parent_buf,
                                pslot - 1, &left_buf);
                left = &left_buf->node;
                orig_slot += left->header.nritems;
                wret = push_node_left(root, left_buf, mid_buf);
                if (wret < 0)
                        ret = wret;
        }

        /*
         * then try to empty the right most buffer into the middle
         */
        if (right_buf) {
                btrfs_cow_block(root, right_buf, parent_buf,
                                pslot + 1, &right_buf);
                right = &right_buf->node;
                wret = push_node_left(root, mid_buf, right_buf);
                if (wret < 0)
                        ret = wret;
                if (right->header.nritems == 0) {
                        u64 blocknr = right_buf->blocknr;
                        tree_block_release(root, right_buf);
                        clean_tree_block(root, right_buf);
                        right_buf = NULL;
                        right = NULL;
                        wret = del_ptr(root, path, level + 1, pslot + 1);
                        if (wret)
                                ret = wret;
                        wret = free_extent(root, blocknr, 1);
                        if (wret)
                                ret = wret;
                } else {
                        memcpy(parent->keys + pslot + 1, right->keys,
                                sizeof(struct key));
                        BUG_ON(list_empty(&parent_buf->dirty));
                }
        }
        if (mid->header.nritems == 1) {
                /*
                 * we're not allowed to leave a node with one item in the
                 * tree during a delete.  A deletion from lower in the tree
                 * could try to delete the only pointer in this node.
                 * So, pull some keys from the left.
                 * There has to be a left pointer at this point because
                 * otherwise we would have pulled some pointers from the
                 * right
                 */
                BUG_ON(!left_buf);
                wret = balance_node_right(root, mid_buf, left_buf);
                if (wret < 0)
                        ret = wret;
                BUG_ON(wret == 1);
        }
        if (mid->header.nritems == 0) {
                /* we've managed to empty the middle node, drop it */
                u64 blocknr = mid_buf->blocknr;
                tree_block_release(root, mid_buf);
                clean_tree_block(root, mid_buf);
                mid_buf = NULL;
                mid = NULL;
                wret = del_ptr(root, path, level + 1, pslot);
                if (wret)
                        ret = wret;
                wret = free_extent(root, blocknr, 1);
                if (wret)
                        ret = wret;
        } else {
                /* update the parent key to reflect our changes */
                memcpy(parent->keys + pslot, mid->keys, sizeof(struct key));
                BUG_ON(list_empty(&parent_buf->dirty));
        }

        /* update the path */
        if (left_buf) {
                if (left->header.nritems > orig_slot) {
                        left_buf->count++; // released below
                        path->nodes[level] = left_buf;
                        path->slots[level + 1] -= 1;
                        path->slots[level] = orig_slot;
                        if (mid_buf)
                                tree_block_release(root, mid_buf);
                } else {
                        orig_slot -= left->header.nritems;
                        path->slots[level] = orig_slot;
                }
        }
        /* double check we haven't messed things up */
        check_block(path, level);
        if (orig_ptr != path->nodes[level]->node.blockptrs[path->slots[level]])
                BUG();

        if (right_buf)
                tree_block_release(root, right_buf);
        if (left_buf)
                tree_block_release(root, left_buf);
        return ret;
}

/*
 * look for key in the tree.  path is filled in with nodes along the way
 * if key is found, we return zero and you can find the item in the leaf
 * level of the path (level 0)
 *
 * If the key isn't found, the path points to the slot where it should
 * be inserted, and 1 is returned.  If there are other errors during the
 * search a negative error number is returned.
 *
 * if ins_len > 0, nodes and leaves will be split as we walk down the
 * tree.  if ins_len < 0, nodes will be merged as we walk down the tree (if
 * possible)
 */
int search_slot(struct ctree_root *root, struct key *key,
                struct ctree_path *p, int ins_len, int cow)
{
        struct tree_buffer *b;
        struct tree_buffer *cow_buf;
        struct node *c;
        int slot;
        int ret;
        int level;

again:
        b = root->node;
        b->count++;
        while (b) {
                level = node_level(b->node.header.flags);
                if (cow) {
                        int wret;
                        wret = btrfs_cow_block(root, b, p->nodes[level + 1],
                                               p->slots[level + 1], &cow_buf);
                        b = cow_buf;
                }
                BUG_ON(!cow && ins_len);
                c = &b->node;
                p->nodes[level] = b;
                ret = check_block(p, level);
                if (ret)
                        return -1;
                ret = bin_search(c, key, &slot);
                if (!is_leaf(c->header.flags)) {
                        if (ret && slot > 0)
                                slot -= 1;
                        p->slots[level] = slot;
                        if (ins_len > 0 &&
                            c->header.nritems == NODEPTRS_PER_BLOCK) {
                                int sret = split_node(root, p, level);
                                BUG_ON(sret > 0);
                                if (sret)
                                        return sret;
                                b = p->nodes[level];
                                c = &b->node;
                                slot = p->slots[level];
                        } else if (ins_len < 0) {
                                int sret = balance_level(root, p, level);
                                if (sret)
                                        return sret;
                                b = p->nodes[level];
                                if (!b)
                                        goto again;
                                c = &b->node;
                                slot = p->slots[level];
                                BUG_ON(c->header.nritems == 1);
                        }
                        b = read_tree_block(root, c->blockptrs[slot]);
                } else {
                        struct leaf *l = (struct leaf *)c;
                        p->slots[level] = slot;
                        if (ins_len > 0 && leaf_free_space(l) <
                            sizeof(struct item) + ins_len) {
                                int sret = split_leaf(root, p, ins_len);
                                BUG_ON(sret > 0);
                                if (sret)
                                        return sret;
                        }
                        BUG_ON(root->node->count == 1);
                        return ret;
                }
        }
        BUG_ON(root->node->count == 1);
        return 1;
}

/*
 * adjust the pointers going up the tree, starting at level
 * making sure the right key of each node is points to 'key'.
 * This is used after shifting pointers to the left, so it stops
 * fixing up pointers when a given leaf/node is not in slot 0 of the
 * higher levels
 *
 * If this fails to write a tree block, it returns -1, but continues
 * fixing up the blocks in ram so the tree is consistent.
 */
static int fixup_low_keys(struct ctree_root *root,
                           struct ctree_path *path, struct key *key,
                           int level)
{
        int i;
        int ret = 0;
        for (i = level; i < MAX_LEVEL; i++) {
                struct node *t;
                int tslot = path->slots[i];
                if (!path->nodes[i])
                        break;
                t = &path->nodes[i]->node;
                memcpy(t->keys + tslot, key, sizeof(*key));
                BUG_ON(list_empty(&path->nodes[i]->dirty));
                if (tslot != 0)
                        break;
        }
        return ret;
}

/*
 * try to push data from one node into the next node left in the
 * tree.
 *
 * returns 0 if some ptrs were pushed left, < 0 if there was some horrible
 * error, and > 0 if there was no room in the left hand block.
 */
static int push_node_left(struct ctree_root *root, struct tree_buffer *dst_buf,
                          struct tree_buffer *src_buf)
{
        struct node *src = &src_buf->node;
        struct node *dst = &dst_buf->node;
        int push_items = 0;
        int src_nritems;
        int dst_nritems;
        int ret = 0;

        src_nritems = src->header.nritems;
        dst_nritems = dst->header.nritems;
        push_items = NODEPTRS_PER_BLOCK - dst_nritems;
        if (push_items <= 0) {
                return 1;
        }

        if (src_nritems < push_items)
                push_items = src_nritems;

        memcpy(dst->keys + dst_nritems, src->keys,
                push_items * sizeof(struct key));
        memcpy(dst->blockptrs + dst_nritems, src->blockptrs,
                push_items * sizeof(u64));
        if (push_items < src_nritems) {
                memmove(src->keys, src->keys + push_items,
                        (src_nritems - push_items) * sizeof(struct key));
                memmove(src->blockptrs, src->blockptrs + push_items,
                        (src_nritems - push_items) * sizeof(u64));
        }
        src->header.nritems -= push_items;
        dst->header.nritems += push_items;

        BUG_ON(list_empty(&src_buf->dirty));
        BUG_ON(list_empty(&dst_buf->dirty));
        return ret;
}

/*
 * try to push data from one node into the next node right in the
 * tree.
 *
 * returns 0 if some ptrs were pushed, < 0 if there was some horrible
 * error, and > 0 if there was no room in the right hand block.
 *
 * this will  only push up to 1/2 the contents of the left node over
 */
static int balance_node_right(struct ctree_root *root,
                              struct tree_buffer *dst_buf,
                              struct tree_buffer *src_buf)
{
        struct node *src = &src_buf->node;
        struct node *dst = &dst_buf->node;
        int push_items = 0;
        int max_push;
        int src_nritems;
        int dst_nritems;
        int ret = 0;

        src_nritems = src->header.nritems;
        dst_nritems = dst->header.nritems;
        push_items = NODEPTRS_PER_BLOCK - dst_nritems;
        if (push_items <= 0) {
                return 1;
        }

        max_push = src_nritems / 2 + 1;
        /* don't try to empty the node */
        if (max_push > src_nritems)
                return 1;
        if (max_push < push_items)
                push_items = max_push;

        memmove(dst->keys + push_items, dst->keys,
                dst_nritems * sizeof(struct key));
        memmove(dst->blockptrs + push_items, dst->blockptrs,
                dst_nritems * sizeof(u64));
        memcpy(dst->keys, src->keys + src_nritems - push_items,
                push_items * sizeof(struct key));
        memcpy(dst->blockptrs, src->blockptrs + src_nritems - push_items,
                push_items * sizeof(u64));

        src->header.nritems -= push_items;
        dst->header.nritems += push_items;

        BUG_ON(list_empty(&src_buf->dirty));
        BUG_ON(list_empty(&dst_buf->dirty));
        return ret;
}

/*
 * helper function to insert a new root level in the tree.
 * A new node is allocated, and a single item is inserted to
 * point to the existing root
 *
 * returns zero on success or < 0 on failure.
 */
static int insert_new_root(struct ctree_root *root,
                           struct ctree_path *path, int level)
{
        struct tree_buffer *t;
        struct node *lower;
        struct node *c;
        struct key *lower_key;

        BUG_ON(path->nodes[level]);
        BUG_ON(path->nodes[level-1] != root->node);

        t = alloc_free_block(root);
        c = &t->node;
        memset(c, 0, sizeof(c));
        c->header.nritems = 1;
        c->header.flags = node_level(level);
        c->header.blocknr = t->blocknr;
        c->header.parentid = root->node->node.header.parentid;
        lower = &path->nodes[level-1]->node;
        if (is_leaf(lower->header.flags))
                lower_key = &((struct leaf *)lower)->items[0].key;
        else
                lower_key = lower->keys;
        memcpy(c->keys, lower_key, sizeof(struct key));
        c->blockptrs[0] = path->nodes[level-1]->blocknr;
        /* the super has an extra ref to root->node */
        tree_block_release(root, root->node);
        root->node = t;
        t->count++;
        path->nodes[level] = t;
        path->slots[level] = 0;
        return 0;
}

/*
 * worker function to insert a single pointer in a node.
 * the node should have enough room for the pointer already
 *
 * slot and level indicate where you want the key to go, and
 * blocknr is the block the key points to.
 *
 * returns zero on success and < 0 on any error
 */
static int insert_ptr(struct ctree_root *root,
                struct ctree_path *path, struct key *key,
                u64 blocknr, int slot, int level)
{
        struct node *lower;
        int nritems;

        BUG_ON(!path->nodes[level]);
        lower = &path->nodes[level]->node;
        nritems = lower->header.nritems;
        if (slot > nritems)
                BUG();
        if (nritems == NODEPTRS_PER_BLOCK)
                BUG();
        if (slot != nritems) {
                memmove(lower->keys + slot + 1, lower->keys + slot,
                        (nritems - slot) * sizeof(struct key));
                memmove(lower->blockptrs + slot + 1, lower->blockptrs + slot,
                        (nritems - slot) * sizeof(u64));
        }
        memcpy(lower->keys + slot, key, sizeof(struct key));
        lower->blockptrs[slot] = blocknr;
        lower->header.nritems++;
        if (lower->keys[1].objectid == 0)
                        BUG();
        BUG_ON(list_empty(&path->nodes[level]->dirty));
        return 0;
}

/*
 * split the node at the specified level in path in two.
 * The path is corrected to point to the appropriate node after the split
 *
 * Before splitting this tries to make some room in the node by pushing
 * left and right, if either one works, it returns right away.
 *
 * returns 0 on success and < 0 on failure
 */
static int split_node(struct ctree_root *root, struct ctree_path *path,
                      int level)
{
        struct tree_buffer *t;
        struct node *c;
        struct tree_buffer *split_buffer;
        struct node *split;
        int mid;
        int ret;
        int wret;

        t = path->nodes[level];
        c = &t->node;
        if (t == root->node) {
                /* trying to split the root, lets make a new one */
                ret = insert_new_root(root, path, level + 1);
                if (ret)
                        return ret;
        }
        split_buffer = alloc_free_block(root);
        split = &split_buffer->node;
        split->header.flags = c->header.flags;
        split->header.blocknr = split_buffer->blocknr;
        split->header.parentid = root->node->node.header.parentid;
        mid = (c->header.nritems + 1) / 2;
        memcpy(split->keys, c->keys + mid,
                (c->header.nritems - mid) * sizeof(struct key));
        memcpy(split->blockptrs, c->blockptrs + mid,
                (c->header.nritems - mid) * sizeof(u64));
        split->header.nritems = c->header.nritems - mid;
        c->header.nritems = mid;
        ret = 0;

        BUG_ON(list_empty(&t->dirty));
        wret = insert_ptr(root, path, split->keys, split_buffer->blocknr,
                          path->slots[level + 1] + 1, level + 1);
        if (wret)
                ret = wret;

        if (path->slots[level] >= mid) {
                path->slots[level] -= mid;
                tree_block_release(root, t);
                path->nodes[level] = split_buffer;
                path->slots[level + 1] += 1;
        } else {
                tree_block_release(root, split_buffer);
        }
        return ret;
}

/*
 * how many bytes are required to store the items in a leaf.  start
 * and nr indicate which items in the leaf to check.  This totals up the
 * space used both by the item structs and the item data
 */
static int leaf_space_used(struct leaf *l, int start, int nr)
{
        int data_len;
        int end = start + nr - 1;

        if (!nr)
                return 0;
        data_len = l->items[start].offset + l->items[start].size;
        data_len = data_len - l->items[end].offset;
        data_len += sizeof(struct item) * nr;
        return data_len;
}

/*
 * push some data in the path leaf to the right, trying to free up at
 * least data_size bytes.  returns zero if the push worked, nonzero otherwise
 *
 * returns 1 if the push failed because the other node didn't have enough
 * room, 0 if everything worked out and < 0 if there were major errors.
 */
static int push_leaf_right(struct ctree_root *root, struct ctree_path *path,
                           int data_size)
{
        struct tree_buffer *left_buf = path->nodes[0];
        struct leaf *left = &left_buf->leaf;
        struct leaf *right;
        struct tree_buffer *right_buf;
        struct tree_buffer *upper;
        int slot;
        int i;
        int free_space;
        int push_space = 0;
        int push_items = 0;
        struct item *item;

        slot = path->slots[1];
        if (!path->nodes[1]) {
                return 1;
        }
        upper = path->nodes[1];
        if (slot >= upper->node.header.nritems - 1) {
                return 1;
        }
        right_buf = read_tree_block(root, upper->node.blockptrs[slot + 1]);
        right = &right_buf->leaf;
        free_space = leaf_free_space(right);
        if (free_space < data_size + sizeof(struct item)) {
                tree_block_release(root, right_buf);
                return 1;
        }
        /* cow and double check */
        btrfs_cow_block(root, right_buf, upper, slot + 1, &right_buf);
        right = &right_buf->leaf;
        free_space = leaf_free_space(right);
        if (free_space < data_size + sizeof(struct item)) {
                tree_block_release(root, right_buf);
                return 1;
        }

        for (i = left->header.nritems - 1; i >= 0; i--) {
                item = left->items + i;
                if (path->slots[0] == i)
                        push_space += data_size + sizeof(*item);
                if (item->size + sizeof(*item) + push_space > free_space)
                        break;
                push_items++;
                push_space += item->size + sizeof(*item);
        }
        if (push_items == 0) {
                tree_block_release(root, right_buf);
                return 1;
        }
        /* push left to right */
        push_space = left->items[left->header.nritems - push_items].offset +
                     left->items[left->header.nritems - push_items].size;
        push_space -= leaf_data_end(left);
        /* make room in the right data area */
        memmove(right->data + leaf_data_end(right) - push_space,
                right->data + leaf_data_end(right),
                LEAF_DATA_SIZE - leaf_data_end(right));
        /* copy from the left data area */
        memcpy(right->data + LEAF_DATA_SIZE - push_space,
                left->data + leaf_data_end(left),
                push_space);
        memmove(right->items + push_items, right->items,
                right->header.nritems * sizeof(struct item));
        /* copy the items from left to right */
        memcpy(right->items, left->items + left->header.nritems - push_items,
                push_items * sizeof(struct item));

        /* update the item pointers */
        right->header.nritems += push_items;
        push_space = LEAF_DATA_SIZE;
        for (i = 0; i < right->header.nritems; i++) {
                right->items[i].offset = push_space - right->items[i].size;
                push_space = right->items[i].offset;
        }
        left->header.nritems -= push_items;

        BUG_ON(list_empty(&left_buf->dirty));
        BUG_ON(list_empty(&right_buf->dirty));
        memcpy(upper->node.keys + slot + 1,
                &right->items[0].key, sizeof(struct key));
        BUG_ON(list_empty(&upper->dirty));

        /* then fixup the leaf pointer in the path */
        if (path->slots[0] >= left->header.nritems) {
                path->slots[0] -= left->header.nritems;
                tree_block_release(root, path->nodes[0]);
                path->nodes[0] = right_buf;
                path->slots[1] += 1;
        } else {
                tree_block_release(root, right_buf);
        }
        return 0;
}
/*
 * push some data in the path leaf to the left, trying to free up at
 * least data_size bytes.  returns zero if the push worked, nonzero otherwise
 */
static int push_leaf_left(struct ctree_root *root, struct ctree_path *path,
                          int data_size)
{
        struct tree_buffer *right_buf = path->nodes[0];
        struct leaf *right = &right_buf->leaf;
        struct tree_buffer *t;
        struct leaf *left;
        int slot;
        int i;
        int free_space;
        int push_space = 0;
        int push_items = 0;
        struct item *item;
        int old_left_nritems;
        int ret = 0;
        int wret;

        slot = path->slots[1];
        if (slot == 0) {
                return 1;
        }
        if (!path->nodes[1]) {
                return 1;
        }
        t = read_tree_block(root, path->nodes[1]->node.blockptrs[slot - 1]);
        left = &t->leaf;
        free_space = leaf_free_space(left);
        if (free_space < data_size + sizeof(struct item)) {
                tree_block_release(root, t);
                return 1;
        }

        /* cow and double check */
        btrfs_cow_block(root, t, path->nodes[1], slot - 1, &t);
        left = &t->leaf;
        free_space = leaf_free_space(left);
        if (free_space < data_size + sizeof(struct item)) {
                tree_block_release(root, t);
                return 1;
        }

        for (i = 0; i < right->header.nritems; i++) {
                item = right->items + i;
                if (path->slots[0] == i)
                        push_space += data_size + sizeof(*item);
                if (item->size + sizeof(*item) + push_space > free_space)
                        break;
                push_items++;
                push_space += item->size + sizeof(*item);
        }
        if (push_items == 0) {
                tree_block_release(root, t);
                return 1;
        }
        /* push data from right to left */
        memcpy(left->items + left->header.nritems,
                right->items, push_items * sizeof(struct item));
        push_space = LEAF_DATA_SIZE - right->items[push_items -1].offset;
        memcpy(left->data + leaf_data_end(left) - push_space,
                right->data + right->items[push_items - 1].offset,
                push_space);
        old_left_nritems = left->header.nritems;
        BUG_ON(old_left_nritems < 0);

        for(i = old_left_nritems; i < old_left_nritems + push_items; i++) {
                left->items[i].offset -= LEAF_DATA_SIZE -
                        left->items[old_left_nritems -1].offset;
        }
        left->header.nritems += push_items;

        /* fixup right node */
        push_space = right->items[push_items-1].offset - leaf_data_end(right);
        memmove(right->data + LEAF_DATA_SIZE - push_space, right->data +
                leaf_data_end(right), push_space);
        memmove(right->items, right->items + push_items,
                (right->header.nritems - push_items) * sizeof(struct item));
        right->header.nritems -= push_items;
        push_space = LEAF_DATA_SIZE;

        for (i = 0; i < right->header.nritems; i++) {
                right->items[i].offset = push_space - right->items[i].size;
                push_space = right->items[i].offset;
        }

        BUG_ON(list_empty(&t->dirty));
        BUG_ON(list_empty(&right_buf->dirty));

        wret = fixup_low_keys(root, path, &right->items[0].key, 1);
        if (wret)
                ret = wret;

        /* then fixup the leaf pointer in the path */
        if (path->slots[0] < push_items) {
                path->slots[0] += old_left_nritems;
                tree_block_release(root, path->nodes[0]);
                path->nodes[0] = t;
                path->slots[1] -= 1;
        } else {
                tree_block_release(root, t);
                path->slots[0] -= push_items;
        }
        BUG_ON(path->slots[0] < 0);
        return ret;
}

/*
 * split the path's leaf in two, making sure there is at least data_size
 * available for the resulting leaf level of the path.
 *
 * returns 0 if all went well and < 0 on failure.
 */
static int split_leaf(struct ctree_root *root, struct ctree_path *path,
                      int data_size)
{
        struct tree_buffer *l_buf;
        struct leaf *l;
        int nritems;
        int mid;
        int slot;
        struct leaf *right;
        struct tree_buffer *right_buffer;
        int space_needed = data_size + sizeof(struct item);
        int data_copy_size;
        int rt_data_off;
        int i;
        int ret;
        int wret;

        wret = push_leaf_left(root, path, data_size);
        if (wret < 0)
                return wret;
        if (wret) {
                wret = push_leaf_right(root, path, data_size);
                if (wret < 0)
                        return wret;
        }

        l_buf = path->nodes[0];
        l = &l_buf->leaf;

        /* did the pushes work? */
        if (leaf_free_space(l) >= sizeof(struct item) + data_size)
                return 0;

        if (!path->nodes[1]) {
                ret = insert_new_root(root, path, 1);
                if (ret)
                        return ret;
        }
        slot = path->slots[0];
        nritems = l->header.nritems;
        mid = (nritems + 1)/ 2;

        right_buffer = alloc_free_block(root);
        BUG_ON(!right_buffer);
        BUG_ON(mid == nritems);
        right = &right_buffer->leaf;
        memset(right, 0, sizeof(*right));
        if (mid <= slot) {
                /* FIXME, just alloc a new leaf here */
                if (leaf_space_used(l, mid, nritems - mid) + space_needed >
                        LEAF_DATA_SIZE)
                        BUG();
        } else {
                /* FIXME, just alloc a new leaf here */
                if (leaf_space_used(l, 0, mid + 1) + space_needed >
                        LEAF_DATA_SIZE)
                        BUG();
        }
        right->header.nritems = nritems - mid;
        right->header.blocknr = right_buffer->blocknr;
        right->header.flags = node_level(0);
        right->header.parentid = root->node->node.header.parentid;
        data_copy_size = l->items[mid].offset + l->items[mid].size -
                         leaf_data_end(l);
        memcpy(right->items, l->items + mid,
               (nritems - mid) * sizeof(struct item));
        memcpy(right->data + LEAF_DATA_SIZE - data_copy_size,
               l->data + leaf_data_end(l), data_copy_size);
        rt_data_off = LEAF_DATA_SIZE -
                     (l->items[mid].offset + l->items[mid].size);

        for (i = 0; i < right->header.nritems; i++)
                right->items[i].offset += rt_data_off;

        l->header.nritems = mid;
        ret = 0;
        wret = insert_ptr(root, path, &right->items[0].key,
                          right_buffer->blocknr, path->slots[1] + 1, 1);
        if (wret)
                ret = wret;
        BUG_ON(list_empty(&right_buffer->dirty));
        BUG_ON(list_empty(&l_buf->dirty));
        BUG_ON(path->slots[0] != slot);
        if (mid <= slot) {
                tree_block_release(root, path->nodes[0]);
                path->nodes[0] = right_buffer;
                path->slots[0] -= mid;
                path->slots[1] += 1;
        } else
                tree_block_release(root, right_buffer);
        BUG_ON(path->slots[0] < 0);
        return ret;
}

/*
 * Given a key and some data, insert an item into the tree.
 * This does all the path init required, making room in the tree if needed.
 */
int insert_item(struct ctree_root *root, struct key *key,
                          void *data, int data_size)
{
        int ret = 0;
        int slot;
        int slot_orig;
        struct leaf *leaf;
        struct tree_buffer *leaf_buf;
        unsigned int nritems;
        unsigned int data_end;
        struct ctree_path path;

        /* create a root if there isn't one */
        if (!root->node)
                BUG();
        init_path(&path);
        ret = search_slot(root, key, &path, data_size, 1);
        if (ret == 0) {
                release_path(root, &path);
                return -EEXIST;
        }
        if (ret < 0)
                goto out;

        slot_orig = path.slots[0];
        leaf_buf = path.nodes[0];
        leaf = &leaf_buf->leaf;

        nritems = leaf->header.nritems;
        data_end = leaf_data_end(leaf);

        if (leaf_free_space(leaf) <  sizeof(struct item) + data_size)
                BUG();

        slot = path.slots[0];
        BUG_ON(slot < 0);
        if (slot != nritems) {
                int i;
                unsigned int old_data = leaf->items[slot].offset +
                                        leaf->items[slot].size;

                /*
                 * item0..itemN ... dataN.offset..dataN.size .. data0.size
                 */
                /* first correct the data pointers */
                for (i = slot; i < nritems; i++)
                        leaf->items[i].offset -= data_size;

                /* shift the items */
                memmove(leaf->items + slot + 1, leaf->items + slot,
                        (nritems - slot) * sizeof(struct item));

                /* shift the data */
                memmove(leaf->data + data_end - data_size, leaf->data +
                        data_end, old_data - data_end);
                data_end = old_data;
        }
        /* copy the new data in */
        memcpy(&leaf->items[slot].key, key, sizeof(struct key));
        leaf->items[slot].offset = data_end - data_size;
        leaf->items[slot].size = data_size;
        memcpy(leaf->data + data_end - data_size, data, data_size);
        leaf->header.nritems += 1;

        ret = 0;
        if (slot == 0)
                ret = fixup_low_keys(root, &path, key, 1);

        BUG_ON(list_empty(&leaf_buf->dirty));
        if (leaf_free_space(leaf) < 0)
                BUG();
        check_leaf(&path, 0);
out:
        release_path(root, &path);
        return ret;
}

/*
 * delete the pointer from a given node.
 *
 * If the delete empties a node, the node is removed from the tree,
 * continuing all the way the root if required.  The root is converted into
 * a leaf if all the nodes are emptied.
 */
static int del_ptr(struct ctree_root *root, struct ctree_path *path, int level,
                   int slot)
{
        struct node *node;
        struct tree_buffer *parent = path->nodes[level];
        int nritems;
        int ret = 0;
        int wret;

        node = &parent->node;
        nritems = node->header.nritems;

        if (slot != nritems -1) {
                memmove(node->keys + slot, node->keys + slot + 1,
                        sizeof(struct key) * (nritems - slot - 1));
                memmove(node->blockptrs + slot,
                        node->blockptrs + slot + 1,
                        sizeof(u64) * (nritems - slot - 1));
        }
        node->header.nritems--;
        if (node->header.nritems == 0 && parent == root->node) {
                BUG_ON(node_level(root->node->node.header.flags) != 1);
                /* just turn the root into a leaf and break */
                root->node->node.header.flags = node_level(0);
        } else if (slot == 0) {
                wret = fixup_low_keys(root, path, node->keys, level + 1);
                if (wret)
                        ret = wret;
        }
        BUG_ON(list_empty(&parent->dirty));
        return ret;
}

/*
 * delete the item at the leaf level in path.  If that empties
 * the leaf, remove it from the tree
 */
int del_item(struct ctree_root *root, struct ctree_path *path)
{
        int slot;
        struct leaf *leaf;
        struct tree_buffer *leaf_buf;
        int doff;
        int dsize;
        int ret = 0;
        int wret;

        leaf_buf = path->nodes[0];
        leaf = &leaf_buf->leaf;
        slot = path->slots[0];
        doff = leaf->items[slot].offset;
        dsize = leaf->items[slot].size;

        if (slot != leaf->header.nritems - 1) {
                int i;
                int data_end = leaf_data_end(leaf);
                memmove(leaf->data + data_end + dsize,
                        leaf->data + data_end,
                        doff - data_end);
                for (i = slot + 1; i < leaf->header.nritems; i++)
                        leaf->items[i].offset += dsize;
                memmove(leaf->items + slot, leaf->items + slot + 1,
                        sizeof(struct item) *
                        (leaf->header.nritems - slot - 1));
        }
        leaf->header.nritems -= 1;
        /* delete the leaf if we've emptied it */
        if (leaf->header.nritems == 0) {
                if (leaf_buf == root->node) {
                        leaf->header.flags = node_level(0);
                        BUG_ON(list_empty(&leaf_buf->dirty));
                } else {
                        clean_tree_block(root, leaf_buf);
                        wret = del_ptr(root, path, 1, path->slots[1]);
                        if (wret)
                                ret = wret;
                        wret = free_extent(root, leaf_buf->blocknr, 1);
                        if (wret)
                                ret = wret;
                }
        } else {
                int used = leaf_space_used(leaf, 0, leaf->header.nritems);
                if (slot == 0) {
                        wret = fixup_low_keys(root, path,
                                                   &leaf->items[0].key, 1);
                        if (wret)
                                ret = wret;
                }
                BUG_ON(list_empty(&leaf_buf->dirty));

                /* delete the leaf if it is mostly empty */
                if (used < LEAF_DATA_SIZE / 3) {
                        /* push_leaf_left fixes the path.
                         * make sure the path still points to our leaf
                         * for possible call to del_ptr below
                         */
                        slot = path->slots[1];
                        leaf_buf->count++;
                        wret = push_leaf_left(root, path, 1);
                        if (wret < 0)
                                ret = wret;
                        if (path->nodes[0] == leaf_buf &&
                            leaf->header.nritems) {
                                wret = push_leaf_right(root, path, 1);
                                if (wret < 0)
                                        ret = wret;
                        }
                        if (leaf->header.nritems == 0) {
                                u64 blocknr = leaf_buf->blocknr;
                                clean_tree_block(root, leaf_buf);
                                wret = del_ptr(root, path, 1, slot);
                                if (wret)
                                        ret = wret;
                                tree_block_release(root, leaf_buf);
                                wret = free_extent(root, blocknr, 1);
                                if (wret)
                                        ret = wret;
                        } else {
                                tree_block_release(root, leaf_buf);
                        }
                }
        }
        return ret;
}

/*
 * walk up the tree as far as required to find the next leaf.
 * returns 0 if it found something or 1 if there are no greater leaves.
 * returns < 0 on io errors.
 */
int next_leaf(struct ctree_root *root, struct ctree_path *path)
{
        int slot;
        int level = 1;
        u64 blocknr;
        struct tree_buffer *c;
        struct tree_buffer *next = NULL;

        while(level < MAX_LEVEL) {
                if (!path->nodes[level])
                        return 1;
                slot = path->slots[level] + 1;
                c = path->nodes[level];
                if (slot >= c->node.header.nritems) {
                        level++;
                        continue;
                }
                blocknr = c->node.blockptrs[slot];
                if (next)
                        tree_block_release(root, next);
                next = read_tree_block(root, blocknr);
                break;
        }
        path->slots[level] = slot;
        while(1) {
                level--;
                c = path->nodes[level];
                tree_block_release(root, c);
                path->nodes[level] = next;
                path->slots[level] = 0;
                if (!level)
                        break;
                next = read_tree_block(root, next->node.blockptrs[0]);
        }
        return 0;
}