591 lines
15 KiB
C
591 lines
15 KiB
C
/*
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* Copyright (C) 2011 Red Hat, Inc.
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*
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* This file is released under the GPL.
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*/
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#include "dm-btree.h"
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#include "dm-btree-internal.h"
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#include "dm-transaction-manager.h"
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#include <linux/export.h>
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/*
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* Removing an entry from a btree
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* ==============================
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*
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* A very important constraint for our btree is that no node, except the
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* root, may have fewer than a certain number of entries.
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* (MIN_ENTRIES <= nr_entries <= MAX_ENTRIES).
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*
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* Ensuring this is complicated by the way we want to only ever hold the
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* locks on 2 nodes concurrently, and only change nodes in a top to bottom
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* fashion.
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*
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* Each node may have a left or right sibling. When decending the spine,
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* if a node contains only MIN_ENTRIES then we try and increase this to at
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* least MIN_ENTRIES + 1. We do this in the following ways:
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*
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* [A] No siblings => this can only happen if the node is the root, in which
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* case we copy the childs contents over the root.
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*
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* [B] No left sibling
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* ==> rebalance(node, right sibling)
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*
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* [C] No right sibling
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* ==> rebalance(left sibling, node)
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*
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* [D] Both siblings, total_entries(left, node, right) <= DEL_THRESHOLD
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* ==> delete node adding it's contents to left and right
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*
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* [E] Both siblings, total_entries(left, node, right) > DEL_THRESHOLD
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* ==> rebalance(left, node, right)
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*
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* After these operations it's possible that the our original node no
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* longer contains the desired sub tree. For this reason this rebalancing
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* is performed on the children of the current node. This also avoids
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* having a special case for the root.
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*
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* Once this rebalancing has occurred we can then step into the child node
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* for internal nodes. Or delete the entry for leaf nodes.
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*/
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/*
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* Some little utilities for moving node data around.
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*/
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static void node_shift(struct btree_node *n, int shift)
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{
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uint32_t nr_entries = le32_to_cpu(n->header.nr_entries);
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uint32_t value_size = le32_to_cpu(n->header.value_size);
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if (shift < 0) {
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shift = -shift;
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BUG_ON(shift > nr_entries);
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BUG_ON((void *) key_ptr(n, shift) >= value_ptr(n, shift));
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memmove(key_ptr(n, 0),
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key_ptr(n, shift),
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(nr_entries - shift) * sizeof(__le64));
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memmove(value_ptr(n, 0),
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value_ptr(n, shift),
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(nr_entries - shift) * value_size);
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} else {
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BUG_ON(nr_entries + shift > le32_to_cpu(n->header.max_entries));
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memmove(key_ptr(n, shift),
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key_ptr(n, 0),
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nr_entries * sizeof(__le64));
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memmove(value_ptr(n, shift),
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value_ptr(n, 0),
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nr_entries * value_size);
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}
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}
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static void node_copy(struct btree_node *left, struct btree_node *right, int shift)
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{
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uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
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uint32_t value_size = le32_to_cpu(left->header.value_size);
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BUG_ON(value_size != le32_to_cpu(right->header.value_size));
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if (shift < 0) {
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shift = -shift;
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BUG_ON(nr_left + shift > le32_to_cpu(left->header.max_entries));
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memcpy(key_ptr(left, nr_left),
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key_ptr(right, 0),
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shift * sizeof(__le64));
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memcpy(value_ptr(left, nr_left),
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value_ptr(right, 0),
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shift * value_size);
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} else {
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BUG_ON(shift > le32_to_cpu(right->header.max_entries));
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memcpy(key_ptr(right, 0),
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key_ptr(left, nr_left - shift),
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shift * sizeof(__le64));
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memcpy(value_ptr(right, 0),
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value_ptr(left, nr_left - shift),
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shift * value_size);
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}
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}
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/*
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* Delete a specific entry from a leaf node.
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*/
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static void delete_at(struct btree_node *n, unsigned index)
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{
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unsigned nr_entries = le32_to_cpu(n->header.nr_entries);
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unsigned nr_to_copy = nr_entries - (index + 1);
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uint32_t value_size = le32_to_cpu(n->header.value_size);
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BUG_ON(index >= nr_entries);
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if (nr_to_copy) {
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memmove(key_ptr(n, index),
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key_ptr(n, index + 1),
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nr_to_copy * sizeof(__le64));
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memmove(value_ptr(n, index),
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value_ptr(n, index + 1),
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nr_to_copy * value_size);
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}
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n->header.nr_entries = cpu_to_le32(nr_entries - 1);
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}
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static unsigned merge_threshold(struct btree_node *n)
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{
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return le32_to_cpu(n->header.max_entries) / 3;
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}
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struct child {
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unsigned index;
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struct dm_block *block;
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struct btree_node *n;
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};
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static struct dm_btree_value_type le64_type = {
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.context = NULL,
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.size = sizeof(__le64),
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.inc = NULL,
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.dec = NULL,
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.equal = NULL
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};
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static int init_child(struct dm_btree_info *info, struct btree_node *parent,
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unsigned index, struct child *result)
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{
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int r, inc;
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dm_block_t root;
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result->index = index;
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root = value64(parent, index);
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r = dm_tm_shadow_block(info->tm, root, &btree_node_validator,
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&result->block, &inc);
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if (r)
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return r;
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result->n = dm_block_data(result->block);
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if (inc)
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inc_children(info->tm, result->n, &le64_type);
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*((__le64 *) value_ptr(parent, index)) =
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cpu_to_le64(dm_block_location(result->block));
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return 0;
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}
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static int exit_child(struct dm_btree_info *info, struct child *c)
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{
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return dm_tm_unlock(info->tm, c->block);
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}
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static void shift(struct btree_node *left, struct btree_node *right, int count)
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{
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uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
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uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
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uint32_t max_entries = le32_to_cpu(left->header.max_entries);
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uint32_t r_max_entries = le32_to_cpu(right->header.max_entries);
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BUG_ON(max_entries != r_max_entries);
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BUG_ON(nr_left - count > max_entries);
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BUG_ON(nr_right + count > max_entries);
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if (!count)
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return;
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if (count > 0) {
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node_shift(right, count);
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node_copy(left, right, count);
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} else {
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node_copy(left, right, count);
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node_shift(right, count);
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}
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left->header.nr_entries = cpu_to_le32(nr_left - count);
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right->header.nr_entries = cpu_to_le32(nr_right + count);
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}
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static void __rebalance2(struct dm_btree_info *info, struct btree_node *parent,
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struct child *l, struct child *r)
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{
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struct btree_node *left = l->n;
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struct btree_node *right = r->n;
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uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
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uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
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unsigned threshold = 2 * merge_threshold(left) + 1;
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if (nr_left + nr_right < threshold) {
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/*
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* Merge
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*/
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node_copy(left, right, -nr_right);
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left->header.nr_entries = cpu_to_le32(nr_left + nr_right);
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delete_at(parent, r->index);
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/*
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* We need to decrement the right block, but not it's
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* children, since they're still referenced by left.
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*/
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dm_tm_dec(info->tm, dm_block_location(r->block));
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} else {
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/*
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* Rebalance.
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*/
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unsigned target_left = (nr_left + nr_right) / 2;
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shift(left, right, nr_left - target_left);
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*key_ptr(parent, r->index) = right->keys[0];
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}
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}
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static int rebalance2(struct shadow_spine *s, struct dm_btree_info *info,
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unsigned left_index)
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{
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int r;
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struct btree_node *parent;
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struct child left, right;
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parent = dm_block_data(shadow_current(s));
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r = init_child(info, parent, left_index, &left);
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if (r)
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return r;
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r = init_child(info, parent, left_index + 1, &right);
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if (r) {
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exit_child(info, &left);
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return r;
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}
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__rebalance2(info, parent, &left, &right);
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r = exit_child(info, &left);
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if (r) {
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exit_child(info, &right);
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return r;
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}
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return exit_child(info, &right);
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}
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/*
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* We dump as many entries from center as possible into left, then the rest
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* in right, then rebalance2. This wastes some cpu, but I want something
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* simple atm.
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*/
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static void delete_center_node(struct dm_btree_info *info, struct btree_node *parent,
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struct child *l, struct child *c, struct child *r,
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struct btree_node *left, struct btree_node *center, struct btree_node *right,
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uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
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{
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uint32_t max_entries = le32_to_cpu(left->header.max_entries);
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unsigned shift = min(max_entries - nr_left, nr_center);
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BUG_ON(nr_left + shift > max_entries);
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node_copy(left, center, -shift);
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left->header.nr_entries = cpu_to_le32(nr_left + shift);
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if (shift != nr_center) {
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shift = nr_center - shift;
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BUG_ON((nr_right + shift) > max_entries);
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node_shift(right, shift);
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node_copy(center, right, shift);
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right->header.nr_entries = cpu_to_le32(nr_right + shift);
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}
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*key_ptr(parent, r->index) = right->keys[0];
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delete_at(parent, c->index);
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r->index--;
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dm_tm_dec(info->tm, dm_block_location(c->block));
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__rebalance2(info, parent, l, r);
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}
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/*
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* Redistributes entries among 3 sibling nodes.
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*/
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static void redistribute3(struct dm_btree_info *info, struct btree_node *parent,
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struct child *l, struct child *c, struct child *r,
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struct btree_node *left, struct btree_node *center, struct btree_node *right,
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uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
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{
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int s;
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uint32_t max_entries = le32_to_cpu(left->header.max_entries);
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unsigned target = (nr_left + nr_center + nr_right) / 3;
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BUG_ON(target > max_entries);
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if (nr_left < nr_right) {
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s = nr_left - target;
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if (s < 0 && nr_center < -s) {
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/* not enough in central node */
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shift(left, center, nr_center);
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s = nr_center - target;
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shift(left, right, s);
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nr_right += s;
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} else
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shift(left, center, s);
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shift(center, right, target - nr_right);
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} else {
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s = target - nr_right;
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if (s > 0 && nr_center < s) {
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/* not enough in central node */
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shift(center, right, nr_center);
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s = target - nr_center;
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shift(left, right, s);
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nr_left -= s;
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} else
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shift(center, right, s);
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shift(left, center, nr_left - target);
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}
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*key_ptr(parent, c->index) = center->keys[0];
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*key_ptr(parent, r->index) = right->keys[0];
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}
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static void __rebalance3(struct dm_btree_info *info, struct btree_node *parent,
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struct child *l, struct child *c, struct child *r)
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{
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struct btree_node *left = l->n;
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struct btree_node *center = c->n;
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struct btree_node *right = r->n;
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uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
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uint32_t nr_center = le32_to_cpu(center->header.nr_entries);
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uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
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unsigned threshold = merge_threshold(left) * 4 + 1;
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BUG_ON(left->header.max_entries != center->header.max_entries);
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BUG_ON(center->header.max_entries != right->header.max_entries);
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if ((nr_left + nr_center + nr_right) < threshold)
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delete_center_node(info, parent, l, c, r, left, center, right,
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nr_left, nr_center, nr_right);
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else
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redistribute3(info, parent, l, c, r, left, center, right,
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nr_left, nr_center, nr_right);
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}
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static int rebalance3(struct shadow_spine *s, struct dm_btree_info *info,
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unsigned left_index)
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{
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int r;
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struct btree_node *parent = dm_block_data(shadow_current(s));
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struct child left, center, right;
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/*
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* FIXME: fill out an array?
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*/
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r = init_child(info, parent, left_index, &left);
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if (r)
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return r;
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r = init_child(info, parent, left_index + 1, ¢er);
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if (r) {
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exit_child(info, &left);
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return r;
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}
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r = init_child(info, parent, left_index + 2, &right);
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if (r) {
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exit_child(info, &left);
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exit_child(info, ¢er);
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return r;
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}
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__rebalance3(info, parent, &left, ¢er, &right);
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r = exit_child(info, &left);
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if (r) {
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exit_child(info, ¢er);
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exit_child(info, &right);
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return r;
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}
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r = exit_child(info, ¢er);
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if (r) {
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exit_child(info, &right);
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return r;
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}
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r = exit_child(info, &right);
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if (r)
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return r;
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return 0;
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}
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static int get_nr_entries(struct dm_transaction_manager *tm,
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dm_block_t b, uint32_t *result)
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{
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int r;
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struct dm_block *block;
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struct btree_node *n;
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r = dm_tm_read_lock(tm, b, &btree_node_validator, &block);
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if (r)
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return r;
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n = dm_block_data(block);
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*result = le32_to_cpu(n->header.nr_entries);
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return dm_tm_unlock(tm, block);
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}
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static int rebalance_children(struct shadow_spine *s,
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struct dm_btree_info *info, uint64_t key)
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{
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int i, r, has_left_sibling, has_right_sibling;
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uint32_t child_entries;
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struct btree_node *n;
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n = dm_block_data(shadow_current(s));
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if (le32_to_cpu(n->header.nr_entries) == 1) {
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struct dm_block *child;
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dm_block_t b = value64(n, 0);
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r = dm_tm_read_lock(info->tm, b, &btree_node_validator, &child);
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if (r)
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return r;
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memcpy(n, dm_block_data(child),
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dm_bm_block_size(dm_tm_get_bm(info->tm)));
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r = dm_tm_unlock(info->tm, child);
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if (r)
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return r;
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dm_tm_dec(info->tm, dm_block_location(child));
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return 0;
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}
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i = lower_bound(n, key);
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if (i < 0)
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return -ENODATA;
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r = get_nr_entries(info->tm, value64(n, i), &child_entries);
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if (r)
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return r;
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has_left_sibling = i > 0;
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has_right_sibling = i < (le32_to_cpu(n->header.nr_entries) - 1);
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if (!has_left_sibling)
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r = rebalance2(s, info, i);
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else if (!has_right_sibling)
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r = rebalance2(s, info, i - 1);
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else
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r = rebalance3(s, info, i - 1);
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return r;
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}
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static int do_leaf(struct btree_node *n, uint64_t key, unsigned *index)
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{
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int i = lower_bound(n, key);
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if ((i < 0) ||
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(i >= le32_to_cpu(n->header.nr_entries)) ||
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(le64_to_cpu(n->keys[i]) != key))
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return -ENODATA;
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*index = i;
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return 0;
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}
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/*
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* Prepares for removal from one level of the hierarchy. The caller must
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* call delete_at() to remove the entry at index.
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*/
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static int remove_raw(struct shadow_spine *s, struct dm_btree_info *info,
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struct dm_btree_value_type *vt, dm_block_t root,
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uint64_t key, unsigned *index)
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{
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int i = *index, r;
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struct btree_node *n;
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for (;;) {
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r = shadow_step(s, root, vt);
|
|
if (r < 0)
|
|
break;
|
|
|
|
/*
|
|
* We have to patch up the parent node, ugly, but I don't
|
|
* see a way to do this automatically as part of the spine
|
|
* op.
|
|
*/
|
|
if (shadow_has_parent(s)) {
|
|
__le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
|
|
memcpy(value_ptr(dm_block_data(shadow_parent(s)), i),
|
|
&location, sizeof(__le64));
|
|
}
|
|
|
|
n = dm_block_data(shadow_current(s));
|
|
|
|
if (le32_to_cpu(n->header.flags) & LEAF_NODE)
|
|
return do_leaf(n, key, index);
|
|
|
|
r = rebalance_children(s, info, key);
|
|
if (r)
|
|
break;
|
|
|
|
n = dm_block_data(shadow_current(s));
|
|
if (le32_to_cpu(n->header.flags) & LEAF_NODE)
|
|
return do_leaf(n, key, index);
|
|
|
|
i = lower_bound(n, key);
|
|
|
|
/*
|
|
* We know the key is present, or else
|
|
* rebalance_children would have returned
|
|
* -ENODATA
|
|
*/
|
|
root = value64(n, i);
|
|
}
|
|
|
|
return r;
|
|
}
|
|
|
|
int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
|
|
uint64_t *keys, dm_block_t *new_root)
|
|
{
|
|
unsigned level, last_level = info->levels - 1;
|
|
int index = 0, r = 0;
|
|
struct shadow_spine spine;
|
|
struct btree_node *n;
|
|
|
|
init_shadow_spine(&spine, info);
|
|
for (level = 0; level < info->levels; level++) {
|
|
r = remove_raw(&spine, info,
|
|
(level == last_level ?
|
|
&info->value_type : &le64_type),
|
|
root, keys[level], (unsigned *)&index);
|
|
if (r < 0)
|
|
break;
|
|
|
|
n = dm_block_data(shadow_current(&spine));
|
|
if (level != last_level) {
|
|
root = value64(n, index);
|
|
continue;
|
|
}
|
|
|
|
BUG_ON(index < 0 || index >= le32_to_cpu(n->header.nr_entries));
|
|
|
|
if (info->value_type.dec)
|
|
info->value_type.dec(info->value_type.context,
|
|
value_ptr(n, index));
|
|
|
|
delete_at(n, index);
|
|
}
|
|
|
|
*new_root = shadow_root(&spine);
|
|
exit_shadow_spine(&spine);
|
|
|
|
return r;
|
|
}
|
|
EXPORT_SYMBOL_GPL(dm_btree_remove);
|