aboutsummaryrefslogtreecommitdiffstats
path: root/fs/btrfs/ulist.c
blob: ad993bc2df93eb3d5b0cef4473c09ef96591bc5d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
/*
 * Copyright (C) 2011 STRATO AG
 * written by Arne Jansen <sensille@gmx.net>
 * Distributed under the GNU GPL license version 2.
 */

#include <linux/slab.h>
#include <linux/module.h>
#include "ulist.h"

/*
 * ulist is a generic data structure to hold a collection of unique u64
 * values. The only operations it supports is adding to the list and
 * enumerating it.
 * It is possible to store an auxiliary value along with the key.
 *
 * The implementation is preliminary and can probably be sped up
 * significantly. A first step would be to store the values in an rbtree
 * as soon as ULIST_SIZE is exceeded.
 *
 * A sample usage for ulists is the enumeration of directed graphs without
 * visiting a node twice. The pseudo-code could look like this:
 *
 * ulist = ulist_alloc();
 * ulist_add(ulist, root);
 * elem = NULL;
 *
 * while ((elem = ulist_next(ulist, elem)) {
 * 	for (all child nodes n in elem)
 *		ulist_add(ulist, n);
 *	do something useful with the node;
 * }
 * ulist_free(ulist);
 *
 * This assumes the graph nodes are adressable by u64. This stems from the
 * usage for tree enumeration in btrfs, where the logical addresses are
 * 64 bit.
 *
 * It is also useful for tree enumeration which could be done elegantly
 * recursively, but is not possible due to kernel stack limitations. The
 * loop would be similar to the above.
 */

/**
 * ulist_init - freshly initialize a ulist
 * @ulist:	the ulist to initialize
 *
 * Note: don't use this function to init an already used ulist, use
 * ulist_reinit instead.
 */
void ulist_init(struct ulist *ulist)
{
	ulist->nnodes = 0;
	ulist->nodes = ulist->int_nodes;
	ulist->nodes_alloced = ULIST_SIZE;
}
EXPORT_SYMBOL(ulist_init);

/**
 * ulist_fini - free up additionally allocated memory for the ulist
 * @ulist:	the ulist from which to free the additional memory
 *
 * This is useful in cases where the base 'struct ulist' has been statically
 * allocated.
 */
void ulist_fini(struct ulist *ulist)
{
	/*
	 * The first ULIST_SIZE elements are stored inline in struct ulist.
	 * Only if more elements are alocated they need to be freed.
	 */
	if (ulist->nodes_alloced > ULIST_SIZE)
		kfree(ulist->nodes);
	ulist->nodes_alloced = 0;	/* in case ulist_fini is called twice */
}
EXPORT_SYMBOL(ulist_fini);

/**
 * ulist_reinit - prepare a ulist for reuse
 * @ulist:	ulist to be reused
 *
 * Free up all additional memory allocated for the list elements and reinit
 * the ulist.
 */
void ulist_reinit(struct ulist *ulist)
{
	ulist_fini(ulist);
	ulist_init(ulist);
}
EXPORT_SYMBOL(ulist_reinit);

/**
 * ulist_alloc - dynamically allocate a ulist
 * @gfp_mask:	allocation flags to for base allocation
 *
 * The allocated ulist will be returned in an initialized state.
 */
struct ulist *ulist_alloc(gfp_t gfp_mask)
{
	struct ulist *ulist = kmalloc(sizeof(*ulist), gfp_mask);

	if (!ulist)
		return NULL;

	ulist_init(ulist);

	return ulist;
}
EXPORT_SYMBOL(ulist_alloc);

/**
 * ulist_free - free dynamically allocated ulist
 * @ulist:	ulist to free
 *
 * It is not necessary to call ulist_fini before.
 */
void ulist_free(struct ulist *ulist)
{
	if (!ulist)
		return;
	ulist_fini(ulist);
	kfree(ulist);
}
EXPORT_SYMBOL(ulist_free);

/**
 * ulist_add - add an element to the ulist
 * @ulist:	ulist to add the element to
 * @val:	value to add to ulist
 * @aux:	auxiliary value to store along with val
 * @gfp_mask:	flags to use for allocation
 *
 * Note: locking must be provided by the caller. In case of rwlocks write
 *       locking is needed
 *
 * Add an element to a ulist. The @val will only be added if it doesn't
 * already exist. If it is added, the auxiliary value @aux is stored along with
 * it. In case @val already exists in the ulist, @aux is ignored, even if
 * it differs from the already stored value.
 *
 * ulist_add returns 0 if @val already exists in ulist and 1 if @val has been
 * inserted.
 * In case of allocation failure -ENOMEM is returned and the ulist stays
 * unaltered.
 */
int ulist_add(struct ulist *ulist, u64 val, unsigned long aux,
	      gfp_t gfp_mask)
{
	int i;

	for (i = 0; i < ulist->nnodes; ++i) {
		if (ulist->nodes[i].val == val)
			return 0;
	}

	if (ulist->nnodes >= ulist->nodes_alloced) {
		u64 new_alloced = ulist->nodes_alloced + 128;
		struct ulist_node *new_nodes;
		void *old = NULL;

		/*
		 * if nodes_alloced == ULIST_SIZE no memory has been allocated
		 * yet, so pass NULL to krealloc
		 */
		if (ulist->nodes_alloced > ULIST_SIZE)
			old = ulist->nodes;

		new_nodes = krealloc(old, sizeof(*new_nodes) * new_alloced,
				     gfp_mask);
		if (!new_nodes)
			return -ENOMEM;

		if (!old)
			memcpy(new_nodes, ulist->int_nodes,
			       sizeof(ulist->int_nodes));

		ulist->nodes = new_nodes;
		ulist->nodes_alloced = new_alloced;
	}
	ulist->nodes[ulist->nnodes].val = val;
	ulist->nodes[ulist->nnodes].aux = aux;
	++ulist->nnodes;

	return 1;
}
EXPORT_SYMBOL(ulist_add);

/**
 * ulist_next - iterate ulist
 * @ulist:	ulist to iterate
 * @prev:	previously returned element or %NULL to start iteration
 *
 * Note: locking must be provided by the caller. In case of rwlocks only read
 *       locking is needed
 *
 * This function is used to iterate an ulist. The iteration is started with
 * @prev = %NULL. It returns the next element from the ulist or %NULL when the
 * end is reached. No guarantee is made with respect to the order in which
 * the elements are returned. They might neither be returned in order of
 * addition nor in ascending order.
 * It is allowed to call ulist_add during an enumeration. Newly added items
 * are guaranteed to show up in the running enumeration.
 */
struct ulist_node *ulist_next(struct ulist *ulist, struct ulist_node *prev)
{
	int next;

	if (ulist->nnodes == 0)
		return NULL;

	if (!prev)
		return &ulist->nodes[0];

	next = (prev - ulist->nodes) + 1;
	if (next < 0 || next >= ulist->nnodes)
		return NULL;

	return &ulist->nodes[next];
}
EXPORT_SYMBOL(ulist_next);