fs/btrfs/ulist.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2011 STRATO AG
   4  * written by Arne Jansen <sensille@gmx.net>
   5  */
   6
   7 #include <linux/slab.h>
   8 #include "messages.h"
   9 #include "ulist.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  * Freshly initialize a ulist.
  42  *
  43  * @ulist:      the ulist to initialize
  44  *
  45  * Note: don't use this function to init an already used ulist, use
  46  * ulist_reinit instead.
  47  */
  48 void ulist_init(struct ulist *ulist)
  49 {
  50         INIT_LIST_HEAD(&ulist->nodes);
  51         ulist->root = RB_ROOT;
  52         ulist->nnodes = 0;
  53         ulist->prealloc = NULL;
  54 }
  55
  56 /*
  57  * Free up additionally allocated memory for the ulist.
  58  *
  59  * @ulist:      the ulist from which to free the additional memory
  60  *
  61  * This is useful in cases where the base 'struct ulist' has been statically
  62  * allocated.
  63  */
  64 void ulist_release(struct ulist *ulist)
  65 {
  66         struct ulist_node *node;
  67         struct ulist_node *next;
  68
  69         list_for_each_entry_safe(node, next, &ulist->nodes, list) {
  70                 kfree(node);
  71         }
  72         kfree(ulist->prealloc);
  73         ulist->prealloc = NULL;
  74         ulist->root = RB_ROOT;
  75         INIT_LIST_HEAD(&ulist->nodes);
  76 }
  77
  78 /*
  79  * Prepare a ulist for reuse.
  80  *
  81  * @ulist:      ulist to be reused
  82  *
  83  * Free up all additional memory allocated for the list elements and reinit
  84  * the ulist.
  85  */
  86 void ulist_reinit(struct ulist *ulist)
  87 {
  88         ulist_release(ulist);
  89         ulist_init(ulist);
  90 }
  91
  92 /*
  93  * Dynamically allocate a ulist.
  94  *
  95  * @gfp_mask:   allocation flags to for base allocation
  96  *
  97  * The allocated ulist will be returned in an initialized state.
  98  */
  99 struct ulist *ulist_alloc(gfp_t gfp_mask)
 100 {
 101         struct ulist *ulist = kmalloc(sizeof(*ulist), gfp_mask);
 102
 103         if (!ulist)
 104                 return NULL;
 105
 106         ulist_init(ulist);
 107
 108         return ulist;
 109 }
 110
 111 void ulist_prealloc(struct ulist *ulist, gfp_t gfp_mask)
 112 {
 113         if (!ulist->prealloc)
 114                 ulist->prealloc = kzalloc(sizeof(*ulist->prealloc), gfp_mask);
 115 }
 116
 117 /*
 118  * Free dynamically allocated ulist.
 119  *
 120  * @ulist:      ulist to free
 121  *
 122  * It is not necessary to call ulist_release before.
 123  */
 124 void ulist_free(struct ulist *ulist)
 125 {
 126         if (!ulist)
 127                 return;
 128         ulist_release(ulist);
 129         kfree(ulist);
 130 }
 131
 132 static struct ulist_node *ulist_rbtree_search(struct ulist *ulist, u64 val)
 133 {
 134         struct rb_node *n = ulist->root.rb_node;
 135         struct ulist_node *u = NULL;
 136
 137         while (n) {
 138                 u = rb_entry(n, struct ulist_node, rb_node);
 139                 if (u->val < val)
 140                         n = n->rb_right;
 141                 else if (u->val > val)
 142                         n = n->rb_left;
 143                 else
 144                         return u;
 145         }
 146         return NULL;
 147 }
 148
 149 static void ulist_rbtree_erase(struct ulist *ulist, struct ulist_node *node)
 150 {
 151         rb_erase(&node->rb_node, &ulist->root);
 152         list_del(&node->list);
 153         kfree(node);
 154         BUG_ON(ulist->nnodes == 0);
 155         ulist->nnodes--;
 156 }
 157
 158 static int ulist_rbtree_insert(struct ulist *ulist, struct ulist_node *ins)
 159 {
 160         struct rb_node **p = &ulist->root.rb_node;
 161         struct rb_node *parent = NULL;
 162         struct ulist_node *cur = NULL;
 163
 164         while (*p) {
 165                 parent = *p;
 166                 cur = rb_entry(parent, struct ulist_node, rb_node);
 167
 168                 if (cur->val < ins->val)
 169                         p = &(*p)->rb_right;
 170                 else if (cur->val > ins->val)
 171                         p = &(*p)->rb_left;
 172                 else
 173                         return -EEXIST;
 174         }
 175         rb_link_node(&ins->rb_node, parent, p);
 176         rb_insert_color(&ins->rb_node, &ulist->root);
 177         return 0;
 178 }
 179
 180 /*
 181  * Add an element to the ulist.
 182  *
 183  * @ulist:      ulist to add the element to
 184  * @val:        value to add to ulist
 185  * @aux:        auxiliary value to store along with val
 186  * @gfp_mask:   flags to use for allocation
 187  *
 188  * Note: locking must be provided by the caller. In case of rwlocks write
 189  *       locking is needed
 190  *
 191  * Add an element to a ulist. The @val will only be added if it doesn't
 192  * already exist. If it is added, the auxiliary value @aux is stored along with
 193  * it. In case @val already exists in the ulist, @aux is ignored, even if
 194  * it differs from the already stored value.
 195  *
 196  * ulist_add returns 0 if @val already exists in ulist and 1 if @val has been
 197  * inserted.
 198  * In case of allocation failure -ENOMEM is returned and the ulist stays
 199  * unaltered.
 200  */
 201 int ulist_add(struct ulist *ulist, u64 val, u64 aux, gfp_t gfp_mask)
 202 {
 203         return ulist_add_merge(ulist, val, aux, NULL, gfp_mask);
 204 }
 205
 206 int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux,
 207                     u64 *old_aux, gfp_t gfp_mask)
 208 {
 209         int ret;
 210         struct ulist_node *node;
 211
 212         node = ulist_rbtree_search(ulist, val);
 213         if (node) {
 214                 if (old_aux)
 215                         *old_aux = node->aux;
 216                 return 0;
 217         }
 218
 219         if (ulist->prealloc) {
 220                 node = ulist->prealloc;
 221                 ulist->prealloc = NULL;
 222         } else {
 223                 node = kmalloc(sizeof(*node), gfp_mask);
 224                 if (!node)
 225                         return -ENOMEM;
 226         }
 227
 228         node->val = val;
 229         node->aux = aux;
 230
 231         ret = ulist_rbtree_insert(ulist, node);
 232         ASSERT(!ret);
 233         list_add_tail(&node->list, &ulist->nodes);
 234         ulist->nnodes++;
 235
 236         return 1;
 237 }
 238
 239 /*
 240  * Delete one node from ulist.
 241  *
 242  * @ulist:      ulist to remove node from
 243  * @val:        value to delete
 244  * @aux:        aux to delete
 245  *
 246  * The deletion will only be done when *BOTH* val and aux matches.
 247  * Return 0 for successful delete.
 248  * Return > 0 for not found.
 249  */
 250 int ulist_del(struct ulist *ulist, u64 val, u64 aux)
 251 {
 252         struct ulist_node *node;
 253
 254         node = ulist_rbtree_search(ulist, val);
 255         /* Not found */
 256         if (!node)
 257                 return 1;
 258
 259         if (node->aux != aux)
 260                 return 1;
 261
 262         /* Found and delete */
 263         ulist_rbtree_erase(ulist, node);
 264         return 0;
 265 }
 266
 267 /*
 268  * Iterate ulist.
 269  *
 270  * @ulist:      ulist to iterate
 271  * @uiter:      iterator variable, initialized with ULIST_ITER_INIT(&iterator)
 272  *
 273  * Note: locking must be provided by the caller. In case of rwlocks only read
 274  *       locking is needed
 275  *
 276  * This function is used to iterate an ulist.
 277  * It returns the next element from the ulist or %NULL when the
 278  * end is reached. No guarantee is made with respect to the order in which
 279  * the elements are returned. They might neither be returned in order of
 280  * addition nor in ascending order.
 281  * It is allowed to call ulist_add during an enumeration. Newly added items
 282  * are guaranteed to show up in the running enumeration.
 283  */
 284 struct ulist_node *ulist_next(const struct ulist *ulist, struct ulist_iterator *uiter)
 285 {
 286         struct ulist_node *node;
 287
 288         if (list_empty(&ulist->nodes))
 289                 return NULL;
 290         if (uiter->cur_list && uiter->cur_list->next == &ulist->nodes)
 291                 return NULL;
 292         if (uiter->cur_list) {
 293                 uiter->cur_list = uiter->cur_list->next;
 294         } else {
 295                 uiter->cur_list = ulist->nodes.next;
 296         }
 297         node = list_entry(uiter->cur_list, struct ulist_node, list);
 298         return node;
 299 }