linux/fs/btrfs/ulist.c
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   1/*
   2 * Copyright (C) 2011 STRATO AG
   3 * written by Arne Jansen <sensille@gmx.net>
   4 * Distributed under the GNU GPL license version 2.
   5 */
   6
   7#include <linux/slab.h>
   8#include "ulist.h"
   9#include "ctree.h"
  10
  11/*
  12 * ulist is a generic data structure to hold a collection of unique u64
  13 * values. The only operations it supports is adding to the list and
  14 * enumerating it.
  15 * It is possible to store an auxiliary value along with the key.
  16 *
  17 * A sample usage for ulists is the enumeration of directed graphs without
  18 * visiting a node twice. The pseudo-code could look like this:
  19 *
  20 * ulist = ulist_alloc();
  21 * ulist_add(ulist, root);
  22 * ULIST_ITER_INIT(&uiter);
  23 *
  24 * while ((elem = ulist_next(ulist, &uiter)) {
  25 *      for (all child nodes n in elem)
  26 *              ulist_add(ulist, n);
  27 *      do something useful with the node;
  28 * }
  29 * ulist_free(ulist);
  30 *
  31 * This assumes the graph nodes are adressable by u64. This stems from the
  32 * usage for tree enumeration in btrfs, where the logical addresses are
  33 * 64 bit.
  34 *
  35 * It is also useful for tree enumeration which could be done elegantly
  36 * recursively, but is not possible due to kernel stack limitations. The
  37 * loop would be similar to the above.
  38 */
  39
  40/**
  41 * ulist_init - freshly initialize a ulist
  42 * @ulist:      the ulist to initialize
  43 *
  44 * Note: don't use this function to init an already used ulist, use
  45 * ulist_reinit instead.
  46 */
  47void ulist_init(struct ulist *ulist)
  48{
  49        INIT_LIST_HEAD(&ulist->nodes);
  50        ulist->root = RB_ROOT;
  51        ulist->nnodes = 0;
  52}
  53
  54/**
  55 * ulist_fini - free up additionally allocated memory for the ulist
  56 * @ulist:      the ulist from which to free the additional memory
  57 *
  58 * This is useful in cases where the base 'struct ulist' has been statically
  59 * allocated.
  60 */
  61static void ulist_fini(struct ulist *ulist)
  62{
  63        struct ulist_node *node;
  64        struct ulist_node *next;
  65
  66        list_for_each_entry_safe(node, next, &ulist->nodes, list) {
  67                kfree(node);
  68        }
  69        ulist->root = RB_ROOT;
  70        INIT_LIST_HEAD(&ulist->nodes);
  71}
  72
  73/**
  74 * ulist_reinit - prepare a ulist for reuse
  75 * @ulist:      ulist to be reused
  76 *
  77 * Free up all additional memory allocated for the list elements and reinit
  78 * the ulist.
  79 */
  80void ulist_reinit(struct ulist *ulist)
  81{
  82        ulist_fini(ulist);
  83        ulist_init(ulist);
  84}
  85
  86/**
  87 * ulist_alloc - dynamically allocate a ulist
  88 * @gfp_mask:   allocation flags to for base allocation
  89 *
  90 * The allocated ulist will be returned in an initialized state.
  91 */
  92struct ulist *ulist_alloc(gfp_t gfp_mask)
  93{
  94        struct ulist *ulist = kmalloc(sizeof(*ulist), gfp_mask);
  95
  96        if (!ulist)
  97                return NULL;
  98
  99        ulist_init(ulist);
 100
 101        return ulist;
 102}
 103
 104/**
 105 * ulist_free - free dynamically allocated ulist
 106 * @ulist:      ulist to free
 107 *
 108 * It is not necessary to call ulist_fini before.
 109 */
 110void ulist_free(struct ulist *ulist)
 111{
 112        if (!ulist)
 113                return;
 114        ulist_fini(ulist);
 115        kfree(ulist);
 116}
 117
 118static struct ulist_node *ulist_rbtree_search(struct ulist *ulist, u64 val)
 119{
 120        struct rb_node *n = ulist->root.rb_node;
 121        struct ulist_node *u = NULL;
 122
 123        while (n) {
 124                u = rb_entry(n, struct ulist_node, rb_node);
 125                if (u->val < val)
 126                        n = n->rb_right;
 127                else if (u->val > val)
 128                        n = n->rb_left;
 129                else
 130                        return u;
 131        }
 132        return NULL;
 133}
 134
 135static void ulist_rbtree_erase(struct ulist *ulist, struct ulist_node *node)
 136{
 137        rb_erase(&node->rb_node, &ulist->root);
 138        list_del(&node->list);
 139        kfree(node);
 140        BUG_ON(ulist->nnodes == 0);
 141        ulist->nnodes--;
 142}
 143
 144static int ulist_rbtree_insert(struct ulist *ulist, struct ulist_node *ins)
 145{
 146        struct rb_node **p = &ulist->root.rb_node;
 147        struct rb_node *parent = NULL;
 148        struct ulist_node *cur = NULL;
 149
 150        while (*p) {
 151                parent = *p;
 152                cur = rb_entry(parent, struct ulist_node, rb_node);
 153
 154                if (cur->val < ins->val)
 155                        p = &(*p)->rb_right;
 156                else if (cur->val > ins->val)
 157                        p = &(*p)->rb_left;
 158                else
 159                        return -EEXIST;
 160        }
 161        rb_link_node(&ins->rb_node, parent, p);
 162        rb_insert_color(&ins->rb_node, &ulist->root);
 163        return 0;
 164}
 165
 166/**
 167 * ulist_add - add an element to the ulist
 168 * @ulist:      ulist to add the element to
 169 * @val:        value to add to ulist
 170 * @aux:        auxiliary value to store along with val
 171 * @gfp_mask:   flags to use for allocation
 172 *
 173 * Note: locking must be provided by the caller. In case of rwlocks write
 174 *       locking is needed
 175 *
 176 * Add an element to a ulist. The @val will only be added if it doesn't
 177 * already exist. If it is added, the auxiliary value @aux is stored along with
 178 * it. In case @val already exists in the ulist, @aux is ignored, even if
 179 * it differs from the already stored value.
 180 *
 181 * ulist_add returns 0 if @val already exists in ulist and 1 if @val has been
 182 * inserted.
 183 * In case of allocation failure -ENOMEM is returned and the ulist stays
 184 * unaltered.
 185 */
 186int ulist_add(struct ulist *ulist, u64 val, u64 aux, gfp_t gfp_mask)
 187{
 188        return ulist_add_merge(ulist, val, aux, NULL, gfp_mask);
 189}
 190
 191int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux,
 192                    u64 *old_aux, gfp_t gfp_mask)
 193{
 194        int ret;
 195        struct ulist_node *node;
 196
 197        node = ulist_rbtree_search(ulist, val);
 198        if (node) {
 199                if (old_aux)
 200                        *old_aux = node->aux;
 201                return 0;
 202        }
 203        node = kmalloc(sizeof(*node), gfp_mask);
 204        if (!node)
 205                return -ENOMEM;
 206
 207        node->val = val;
 208        node->aux = aux;
 209
 210        ret = ulist_rbtree_insert(ulist, node);
 211        ASSERT(!ret);
 212        list_add_tail(&node->list, &ulist->nodes);
 213        ulist->nnodes++;
 214
 215        return 1;
 216}
 217
 218/*
 219 * ulist_del - delete one node from ulist
 220 * @ulist:      ulist to remove node from
 221 * @val:        value to delete
 222 * @aux:        aux to delete
 223 *
 224 * The deletion will only be done when *BOTH* val and aux matches.
 225 * Return 0 for successful delete.
 226 * Return > 0 for not found.
 227 */
 228int ulist_del(struct ulist *ulist, u64 val, u64 aux)
 229{
 230        struct ulist_node *node;
 231
 232        node = ulist_rbtree_search(ulist, val);
 233        /* Not found */
 234        if (!node)
 235                return 1;
 236
 237        if (node->aux != aux)
 238                return 1;
 239
 240        /* Found and delete */
 241        ulist_rbtree_erase(ulist, node);
 242        return 0;
 243}
 244
 245/**
 246 * ulist_next - iterate ulist
 247 * @ulist:      ulist to iterate
 248 * @uiter:      iterator variable, initialized with ULIST_ITER_INIT(&iterator)
 249 *
 250 * Note: locking must be provided by the caller. In case of rwlocks only read
 251 *       locking is needed
 252 *
 253 * This function is used to iterate an ulist.
 254 * It returns the next element from the ulist or %NULL when the
 255 * end is reached. No guarantee is made with respect to the order in which
 256 * the elements are returned. They might neither be returned in order of
 257 * addition nor in ascending order.
 258 * It is allowed to call ulist_add during an enumeration. Newly added items
 259 * are guaranteed to show up in the running enumeration.
 260 */
 261struct ulist_node *ulist_next(struct ulist *ulist, struct ulist_iterator *uiter)
 262{
 263        struct ulist_node *node;
 264
 265        if (list_empty(&ulist->nodes))
 266                return NULL;
 267        if (uiter->cur_list && uiter->cur_list->next == &ulist->nodes)
 268                return NULL;
 269        if (uiter->cur_list) {
 270                uiter->cur_list = uiter->cur_list->next;
 271        } else {
 272                uiter->cur_list = ulist->nodes.next;
 273        }
 274        node = list_entry(uiter->cur_list, struct ulist_node, list);
 275        return node;
 276}
 277