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