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 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  */
  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 int ulist_rbtree_insert(struct ulist *ulist, struct ulist_node *ins)
 136 {
 137         struct rb_node **p = &ulist->root.rb_node;
 138         struct rb_node *parent = NULL;
 139         struct ulist_node *cur = NULL;
 140
 141         while (*p) {
 142                 parent = *p;
 143                 cur = rb_entry(parent, struct ulist_node, rb_node);
 144
 145                 if (cur->val < ins->val)
 146                         p = &(*p)->rb_right;
 147                 else if (cur->val > ins->val)
 148                         p = &(*p)->rb_left;
 149                 else
 150                         return -EEXIST;
 151         }
 152         rb_link_node(&ins->rb_node, parent, p);
 153         rb_insert_color(&ins->rb_node, &ulist->root);
 154         return 0;
 155 }
 156
 157 /**
 158  * ulist_add - add an element to the ulist
 159  * @ulist:      ulist to add the element to
 160  * @val:        value to add to ulist
 161  * @aux:        auxiliary value to store along with val
 162  * @gfp_mask:   flags to use for allocation
 163  *
 164  * Note: locking must be provided by the caller. In case of rwlocks write
 165  *       locking is needed
 166  *
 167  * Add an element to a ulist. The @val will only be added if it doesn't
 168  * already exist. If it is added, the auxiliary value @aux is stored along with
 169  * it. In case @val already exists in the ulist, @aux is ignored, even if
 170  * it differs from the already stored value.
 171  *
 172  * ulist_add returns 0 if @val already exists in ulist and 1 if @val has been
 173  * inserted.
 174  * In case of allocation failure -ENOMEM is returned and the ulist stays
 175  * unaltered.
 176  */
 177 int ulist_add(struct ulist *ulist, u64 val, u64 aux, gfp_t gfp_mask)
 178 {
 179         return ulist_add_merge(ulist, val, aux, NULL, gfp_mask);
 180 }
 181
 182 int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux,
 183                     u64 *old_aux, gfp_t gfp_mask)
 184 {
 185         int ret;
 186         struct ulist_node *node;
 187
 188         node = ulist_rbtree_search(ulist, val);
 189         if (node) {
 190                 if (old_aux)
 191                         *old_aux = node->aux;
 192                 return 0;
 193         }
 194         node = kmalloc(sizeof(*node), gfp_mask);
 195         if (!node)
 196                 return -ENOMEM;
 197
 198         node->val = val;
 199         node->aux = aux;
 200 #ifdef CONFIG_BTRFS_DEBUG
 201         node->seqnum = ulist->nnodes;
 202 #endif
 203
 204         ret = ulist_rbtree_insert(ulist, node);
 205         ASSERT(!ret);
 206         list_add_tail(&node->list, &ulist->nodes);
 207         ulist->nnodes++;
 208
 209         return 1;
 210 }
 211
 212 /**
 213  * ulist_next - iterate ulist
 214  * @ulist:      ulist to iterate
 215  * @uiter:      iterator variable, initialized with ULIST_ITER_INIT(&iterator)
 216  *
 217  * Note: locking must be provided by the caller. In case of rwlocks only read
 218  *       locking is needed
 219  *
 220  * This function is used to iterate an ulist.
 221  * It returns the next element from the ulist or %NULL when the
 222  * end is reached. No guarantee is made with respect to the order in which
 223  * the elements are returned. They might neither be returned in order of
 224  * addition nor in ascending order.
 225  * It is allowed to call ulist_add during an enumeration. Newly added items
 226  * are guaranteed to show up in the running enumeration.
 227  */
 228 struct ulist_node *ulist_next(struct ulist *ulist, struct ulist_iterator *uiter)
 229 {
 230         struct ulist_node *node;
 231
 232         if (list_empty(&ulist->nodes))
 233                 return NULL;
 234         if (uiter->cur_list && uiter->cur_list->next == &ulist->nodes)
 235                 return NULL;
 236         if (uiter->cur_list) {
 237                 uiter->cur_list = uiter->cur_list->next;
 238         } else {
 239                 uiter->cur_list = ulist->nodes.next;
 240 #ifdef CONFIG_BTRFS_DEBUG
 241                 uiter->i = 0;
 242 #endif
 243         }
 244         node = list_entry(uiter->cur_list, struct ulist_node, list);
 245 #ifdef CONFIG_BTRFS_DEBUG
 246         ASSERT(node->seqnum == uiter->i);
 247         ASSERT(uiter->i >= 0 && uiter->i < ulist->nnodes);
 248         uiter->i++;
 249 #endif
 250         return node;
 251 }