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 */
 47void 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 */
 61static 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 */
 80void 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 */
 92struct 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 */
110void ulist_free(struct ulist *ulist)
111{
112	if (!ulist)
113		return;
114	ulist_fini(ulist);
115	kfree(ulist);
116}
117
118static 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
135static 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 */
177int 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
182int 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 */
228struct 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}