1
2#define pr_fmt(fmt) "list_sort_test: " fmt
3
4#include <linux/kernel.h>
5#include <linux/bug.h>
6#include <linux/compiler.h>
7#include <linux/export.h>
8#include <linux/string.h>
9#include <linux/list_sort.h>
10#include <linux/list.h>
11
12#define MAX_LIST_LENGTH_BITS 20
13
14/*
15 * Returns a list organized in an intermediate format suited
16 * to chaining of merge() calls: null-terminated, no reserved or
17 * sentinel head node, "prev" links not maintained.
18 */
19static struct list_head *merge(void *priv,
20				int (*cmp)(void *priv, struct list_head *a,
21					struct list_head *b),
22				struct list_head *a, struct list_head *b)
23{
24	struct list_head head, *tail = &head;
25
26	while (a && b) {
27		/* if equal, take 'a' -- important for sort stability */
28		if ((*cmp)(priv, a, b) <= 0) {
29			tail->next = a;
30			a = a->next;
31		} else {
32			tail->next = b;
33			b = b->next;
34		}
35		tail = tail->next;
36	}
37	tail->next = a?:b;
38	return head.next;
39}
40
41/*
42 * Combine final list merge with restoration of standard doubly-linked
43 * list structure.  This approach duplicates code from merge(), but
44 * runs faster than the tidier alternatives of either a separate final
45 * prev-link restoration pass, or maintaining the prev links
46 * throughout.
47 */
48static void merge_and_restore_back_links(void *priv,
49				int (*cmp)(void *priv, struct list_head *a,
50					struct list_head *b),
51				struct list_head *head,
52				struct list_head *a, struct list_head *b)
53{
54	struct list_head *tail = head;
55	u8 count = 0;
56
57	while (a && b) {
58		/* if equal, take 'a' -- important for sort stability */
59		if ((*cmp)(priv, a, b) <= 0) {
60			tail->next = a;
61			a->prev = tail;
62			a = a->next;
63		} else {
64			tail->next = b;
65			b->prev = tail;
66			b = b->next;
67		}
68		tail = tail->next;
69	}
70	tail->next = a ? : b;
71
72	do {
73		/*
74		 * In worst cases this loop may run many iterations.
75		 * Continue callbacks to the client even though no
76		 * element comparison is needed, so the client's cmp()
77		 * routine can invoke cond_resched() periodically.
78		 */
79		if (unlikely(!(++count)))
80			(*cmp)(priv, tail->next, tail->next);
81
82		tail->next->prev = tail;
83		tail = tail->next;
84	} while (tail->next);
85
86	tail->next = head;
87	head->prev = tail;
88}
89
90/**
91 * list_sort - sort a list
92 * @priv: private data, opaque to list_sort(), passed to @cmp
93 * @head: the list to sort
94 * @cmp: the elements comparison function
95 *
96 * This function implements "merge sort", which has O(nlog(n))
97 * complexity.
98 *
99 * The comparison function @cmp must return a negative value if @a
100 * should sort before @b, and a positive value if @a should sort after
101 * @b. If @a and @b are equivalent, and their original relative
102 * ordering is to be preserved, @cmp must return 0.
103 */
104void list_sort(void *priv, struct list_head *head,
105		int (*cmp)(void *priv, struct list_head *a,
106			struct list_head *b))
107{
108	struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
109						-- last slot is a sentinel */
110	int lev;  /* index into part[] */
111	int max_lev = 0;
112	struct list_head *list;
113
114	if (list_empty(head))
115		return;
116
117	memset(part, 0, sizeof(part));
118
119	head->prev->next = NULL;
120	list = head->next;
121
122	while (list) {
123		struct list_head *cur = list;
124		list = list->next;
125		cur->next = NULL;
126
127		for (lev = 0; part[lev]; lev++) {
128			cur = merge(priv, cmp, part[lev], cur);
129			part[lev] = NULL;
130		}
131		if (lev > max_lev) {
132			if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
133				printk_once(KERN_DEBUG "list too long for efficiency\n");
134				lev--;
135			}
136			max_lev = lev;
137		}
138		part[lev] = cur;
139	}
140
141	for (lev = 0; lev < max_lev; lev++)
142		if (part[lev])
143			list = merge(priv, cmp, part[lev], list);
144
145	merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
146}
147EXPORT_SYMBOL(list_sort);
148
149#ifdef CONFIG_TEST_LIST_SORT
150
151#include <linux/slab.h>
152#include <linux/random.h>
153
154/*
155 * The pattern of set bits in the list length determines which cases
156 * are hit in list_sort().
157 */
158#define TEST_LIST_LEN (512+128+2) /* not including head */
159
160#define TEST_POISON1 0xDEADBEEF
161#define TEST_POISON2 0xA324354C
162
163struct debug_el {
164	unsigned int poison1;
165	struct list_head list;
166	unsigned int poison2;
167	int value;
168	unsigned serial;
169};
170
171/* Array, containing pointers to all elements in the test list */
172static struct debug_el **elts __initdata;
173
174static int __init check(struct debug_el *ela, struct debug_el *elb)
175{
176	if (ela->serial >= TEST_LIST_LEN) {
177		pr_err("error: incorrect serial %d\n", ela->serial);
178		return -EINVAL;
179	}
180	if (elb->serial >= TEST_LIST_LEN) {
181		pr_err("error: incorrect serial %d\n", elb->serial);
182		return -EINVAL;
183	}
184	if (elts[ela->serial] != ela || elts[elb->serial] != elb) {
185		pr_err("error: phantom element\n");
186		return -EINVAL;
187	}
188	if (ela->poison1 != TEST_POISON1 || ela->poison2 != TEST_POISON2) {
189		pr_err("error: bad poison: %#x/%#x\n",
190			ela->poison1, ela->poison2);
191		return -EINVAL;
192	}
193	if (elb->poison1 != TEST_POISON1 || elb->poison2 != TEST_POISON2) {
194		pr_err("error: bad poison: %#x/%#x\n",
195			elb->poison1, elb->poison2);
196		return -EINVAL;
197	}
198	return 0;
199}
200
201static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
202{
203	struct debug_el *ela, *elb;
204
205	ela = container_of(a, struct debug_el, list);
206	elb = container_of(b, struct debug_el, list);
207
208	check(ela, elb);
209	return ela->value - elb->value;
210}
211
212static int __init list_sort_test(void)
213{
214	int i, count = 1, err = -ENOMEM;
215	struct debug_el *el;
216	struct list_head *cur;
217	LIST_HEAD(head);
218
219	pr_debug("start testing list_sort()\n");
220
221	elts = kcalloc(TEST_LIST_LEN, sizeof(*elts), GFP_KERNEL);
222	if (!elts) {
223		pr_err("error: cannot allocate memory\n");
224		return err;
225	}
226
227	for (i = 0; i < TEST_LIST_LEN; i++) {
228		el = kmalloc(sizeof(*el), GFP_KERNEL);
229		if (!el) {
230			pr_err("error: cannot allocate memory\n");
231			goto exit;
232		}
233		 /* force some equivalencies */
234		el->value = prandom_u32() % (TEST_LIST_LEN / 3);
235		el->serial = i;
236		el->poison1 = TEST_POISON1;
237		el->poison2 = TEST_POISON2;
238		elts[i] = el;
239		list_add_tail(&el->list, &head);
240	}
241
242	list_sort(NULL, &head, cmp);
243
244	err = -EINVAL;
245	for (cur = head.next; cur->next != &head; cur = cur->next) {
246		struct debug_el *el1;
247		int cmp_result;
248
249		if (cur->next->prev != cur) {
250			pr_err("error: list is corrupted\n");
251			goto exit;
252		}
253
254		cmp_result = cmp(NULL, cur, cur->next);
255		if (cmp_result > 0) {
256			pr_err("error: list is not sorted\n");
257			goto exit;
258		}
259
260		el = container_of(cur, struct debug_el, list);
261		el1 = container_of(cur->next, struct debug_el, list);
262		if (cmp_result == 0 && el->serial >= el1->serial) {
263			pr_err("error: order of equivalent elements not "
264				"preserved\n");
265			goto exit;
266		}
267
268		if (check(el, el1)) {
269			pr_err("error: element check failed\n");
270			goto exit;
271		}
272		count++;
273	}
274	if (head.prev != cur) {
275		pr_err("error: list is corrupted\n");
276		goto exit;
277	}
278
279
280	if (count != TEST_LIST_LEN) {
281		pr_err("error: bad list length %d", count);
282		goto exit;
283	}
284
285	err = 0;
286exit:
287	for (i = 0; i < TEST_LIST_LEN; i++)
288		kfree(elts[i]);
289	kfree(elts);
290	return err;
291}
292module_init(list_sort_test);
293#endif /* CONFIG_TEST_LIST_SORT */
294