summaryrefslogtreecommitdiff
path: root/lib/list_sort.c
blob: 1183fa70a44d26cfc673b6d5d2f645b7026f50dd (plain) (blame)
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
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/list_sort.h>
#include <linux/slab.h>
#include <linux/list.h>

#define MAX_LIST_LENGTH_BITS 20

/*
 * Returns a list organized in an intermediate format suited
 * to chaining of merge() calls: null-terminated, no reserved or
 * sentinel head node, "prev" links not maintained.
 */
static struct list_head *merge(void *priv,
				int (*cmp)(void *priv, struct list_head *a,
					struct list_head *b),
				struct list_head *a, struct list_head *b)
{
	struct list_head head, *tail = &head;

	while (a && b) {
		/* if equal, take 'a' -- important for sort stability */
		if ((*cmp)(priv, a, b) <= 0) {
			tail->next = a;
			a = a->next;
		} else {
			tail->next = b;
			b = b->next;
		}
		tail = tail->next;
	}
	tail->next = a?:b;
	return head.next;
}

/*
 * Combine final list merge with restoration of standard doubly-linked
 * list structure.  This approach duplicates code from merge(), but
 * runs faster than the tidier alternatives of either a separate final
 * prev-link restoration pass, or maintaining the prev links
 * throughout.
 */
static void merge_and_restore_back_links(void *priv,
				int (*cmp)(void *priv, struct list_head *a,
					struct list_head *b),
				struct list_head *head,
				struct list_head *a, struct list_head *b)
{
	struct list_head *tail = head;

	while (a && b) {
		/* if equal, take 'a' -- important for sort stability */
		if ((*cmp)(priv, a, b) <= 0) {
			tail->next = a;
			a->prev = tail;
			a = a->next;
		} else {
			tail->next = b;
			b->prev = tail;
			b = b->next;
		}
		tail = tail->next;
	}
	tail->next = a ? : b;

	do {
		/*
		 * In worst cases this loop may run many iterations.
		 * Continue callbacks to the client even though no
		 * element comparison is needed, so the client's cmp()
		 * routine can invoke cond_resched() periodically.
		 */
		(*cmp)(priv, tail->next, tail->next);

		tail->next->prev = tail;
		tail = tail->next;
	} while (tail->next);

	tail->next = head;
	head->prev = tail;
}

/**
 * list_sort - sort a list
 * @priv: private data, opaque to list_sort(), passed to @cmp
 * @head: the list to sort
 * @cmp: the elements comparison function
 *
 * This function implements "merge sort", which has O(nlog(n))
 * complexity.
 *
 * The comparison function @cmp must return a negative value if @a
 * should sort before @b, and a positive value if @a should sort after
 * @b. If @a and @b are equivalent, and their original relative
 * ordering is to be preserved, @cmp must return 0.
 */
void list_sort(void *priv, struct list_head *head,
		int (*cmp)(void *priv, struct list_head *a,
			struct list_head *b))
{
	struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
						-- last slot is a sentinel */
	int lev;  /* index into part[] */
	int max_lev = 0;
	struct list_head *list;

	if (list_empty(head))
		return;

	memset(part, 0, sizeof(part));

	head->prev->next = NULL;
	list = head->next;

	while (list) {
		struct list_head *cur = list;
		list = list->next;
		cur->next = NULL;

		for (lev = 0; part[lev]; lev++) {
			cur = merge(priv, cmp, part[lev], cur);
			part[lev] = NULL;
		}
		if (lev > max_lev) {
			if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
				printk_once(KERN_DEBUG "list passed to"
					" list_sort() too long for"
					" efficiency\n");
				lev--;
			}
			max_lev = lev;
		}
		part[lev] = cur;
	}

	for (lev = 0; lev < max_lev; lev++)
		if (part[lev])
			list = merge(priv, cmp, part[lev], list);

	merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
}
EXPORT_SYMBOL(list_sort);

#ifdef CONFIG_TEST_LIST_SORT

#include <linux/random.h>

/*
 * The pattern of set bits in the list length determines which cases
 * are hit in list_sort().
 */
#define TEST_LIST_LEN (512+128+2) /* not including head */

#define TEST_POISON1 0xDEADBEEF
#define TEST_POISON2 0xA324354C

struct debug_el {
	unsigned int poison1;
	struct list_head list;
	unsigned int poison2;
	int value;
	unsigned serial;
};

/* Array, containing pointers to all elements in the test list */
static struct debug_el **elts __initdata;

static int __init check(struct debug_el *ela, struct debug_el *elb)
{
	if (ela->serial >= TEST_LIST_LEN) {
		printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
				ela->serial);
		return -EINVAL;
	}
	if (elb->serial >= TEST_LIST_LEN) {
		printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
				elb->serial);
		return -EINVAL;
	}
	if (elts[ela->serial] != ela || elts[elb->serial] != elb) {
		printk(KERN_ERR "list_sort_test: error: phantom element\n");
		return -EINVAL;
	}
	if (ela->poison1 != TEST_POISON1 || ela->poison2 != TEST_POISON2) {
		printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
				ela->poison1, ela->poison2);
		return -EINVAL;
	}
	if (elb->poison1 != TEST_POISON1 || elb->poison2 != TEST_POISON2) {
		printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
				elb->poison1, elb->poison2);
		return -EINVAL;
	}
	return 0;
}

static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
{
	struct debug_el *ela, *elb;

	ela = container_of(a, struct debug_el, list);
	elb = container_of(b, struct debug_el, list);

	check(ela, elb);
	return ela->value - elb->value;
}

static int __init list_sort_test(void)
{
	int i, count = 1, err = -EINVAL;
	struct debug_el *el;
	struct list_head *cur, *tmp;
	LIST_HEAD(head);

	printk(KERN_DEBUG "list_sort_test: start testing list_sort()\n");

	elts = kmalloc(sizeof(void *) * TEST_LIST_LEN, GFP_KERNEL);
	if (!elts) {
		printk(KERN_ERR "list_sort_test: error: cannot allocate "
				"memory\n");
		goto exit;
	}

	for (i = 0; i < TEST_LIST_LEN; i++) {
		el = kmalloc(sizeof(*el), GFP_KERNEL);
		if (!el) {
			printk(KERN_ERR "list_sort_test: error: cannot "
					"allocate memory\n");
			goto exit;
		}
		 /* force some equivalencies */
		el->value = prandom_u32() % (TEST_LIST_LEN / 3);
		el->serial = i;
		el->poison1 = TEST_POISON1;
		el->poison2 = TEST_POISON2;
		elts[i] = el;
		list_add_tail(&el->list, &head);
	}

	list_sort(NULL, &head, cmp);

	for (cur = head.next; cur->next != &head; cur = cur->next) {
		struct debug_el *el1;
		int cmp_result;

		if (cur->next->prev != cur) {
			printk(KERN_ERR "list_sort_test: error: list is "
					"corrupted\n");
			goto exit;
		}

		cmp_result = cmp(NULL, cur, cur->next);
		if (cmp_result > 0) {
			printk(KERN_ERR "list_sort_test: error: list is not "
					"sorted\n");
			goto exit;
		}

		el = container_of(cur, struct debug_el, list);
		el1 = container_of(cur->next, struct debug_el, list);
		if (cmp_result == 0 && el->serial >= el1->serial) {
			printk(KERN_ERR "list_sort_test: error: order of "
					"equivalent elements not preserved\n");
			goto exit;
		}

		if (check(el, el1)) {
			printk(KERN_ERR "list_sort_test: error: element check "
					"failed\n");
			goto exit;
		}
		count++;
	}

	if (count != TEST_LIST_LEN) {
		printk(KERN_ERR "list_sort_test: error: bad list length %d",
				count);
		goto exit;
	}

	err = 0;
exit:
	kfree(elts);
	list_for_each_safe(cur, tmp, &head) {
		list_del(cur);
		kfree(container_of(cur, struct debug_el, list));
	}
	return err;
}
module_init(list_sort_test);
#endif /* CONFIG_TEST_LIST_SORT */