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TOMOYO Linux Cross Reference
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 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 }
277 

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