fs/btrfs/ulist.c

   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 addressable 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  */
  47 void 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  */
  61 static 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  */
  80 void 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  */
  92 struct 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  */
 110 void ulist_free(struct ulist *ulist)
 111 {
 112         if (!ulist)
 113                 return;
 114         ulist_fini(ulist);
 115         kfree(ulist);
 116 }
 117
 118 static 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
 135 static 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
 144 static 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  */
 186 int 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
 191 int 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  */
 228 int 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  */
 261 struct 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 }