1 #include <linux/kernel.h>
2 #include <linux/module.h>
3 #include <linux/list_sort.h>
4 #include <linux/slab.h>
5 #include <linux/list.h>
6
7 #define MAX_LIST_LENGTH_BITS 20
8
9 /*
10 * Returns a list organized in an intermediate format suited
11 * to chaining of merge() calls: null-terminated, no reserved or
12 * sentinel head node, "prev" links not maintained.
13 */
merge(void * priv,int (* cmp)(void * priv,struct list_head * a,struct list_head * b),struct list_head * a,struct list_head * b)14 static struct list_head *merge(void *priv,
15 int (*cmp)(void *priv, struct list_head *a,
16 struct list_head *b),
17 struct list_head *a, struct list_head *b)
18 {
19 struct list_head head, *tail = &head;
20
21 while (a && b) {
22 /* if equal, take 'a' -- important for sort stability */
23 if ((*cmp)(priv, a, b) <= 0) {
24 tail->next = a;
25 a = a->next;
26 } else {
27 tail->next = b;
28 b = b->next;
29 }
30 tail = tail->next;
31 }
32 tail->next = a?:b;
33 return head.next;
34 }
35
36 /*
37 * Combine final list merge with restoration of standard doubly-linked
38 * list structure. This approach duplicates code from merge(), but
39 * runs faster than the tidier alternatives of either a separate final
40 * prev-link restoration pass, or maintaining the prev links
41 * throughout.
42 */
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)43 static void merge_and_restore_back_links(void *priv,
44 int (*cmp)(void *priv, struct list_head *a,
45 struct list_head *b),
46 struct list_head *head,
47 struct list_head *a, struct list_head *b)
48 {
49 struct list_head *tail = head;
50
51 while (a && b) {
52 /* if equal, take 'a' -- important for sort stability */
53 if ((*cmp)(priv, a, b) <= 0) {
54 tail->next = a;
55 a->prev = tail;
56 a = a->next;
57 } else {
58 tail->next = b;
59 b->prev = tail;
60 b = b->next;
61 }
62 tail = tail->next;
63 }
64 tail->next = a ? : b;
65
66 do {
67 /*
68 * In worst cases this loop may run many iterations.
69 * Continue callbacks to the client even though no
70 * element comparison is needed, so the client's cmp()
71 * routine can invoke cond_resched() periodically.
72 */
73 (*cmp)(priv, tail->next, tail->next);
74
75 tail->next->prev = tail;
76 tail = tail->next;
77 } while (tail->next);
78
79 tail->next = head;
80 head->prev = tail;
81 }
82
83 /**
84 * list_sort - sort a list
85 * @priv: private data, opaque to list_sort(), passed to @cmp
86 * @head: the list to sort
87 * @cmp: the elements comparison function
88 *
89 * This function implements "merge sort", which has O(nlog(n))
90 * complexity.
91 *
92 * The comparison function @cmp must return a negative value if @a
93 * should sort before @b, and a positive value if @a should sort after
94 * @b. If @a and @b are equivalent, and their original relative
95 * ordering is to be preserved, @cmp must return 0.
96 */
list_sort(void * priv,struct list_head * head,int (* cmp)(void * priv,struct list_head * a,struct list_head * b))97 void list_sort(void *priv, struct list_head *head,
98 int (*cmp)(void *priv, struct list_head *a,
99 struct list_head *b))
100 {
101 struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
102 -- last slot is a sentinel */
103 int lev; /* index into part[] */
104 int max_lev = 0;
105 struct list_head *list;
106
107 if (list_empty(head))
108 return;
109
110 memset(part, 0, sizeof(part));
111
112 head->prev->next = NULL;
113 list = head->next;
114
115 while (list) {
116 struct list_head *cur = list;
117 list = list->next;
118 cur->next = NULL;
119
120 for (lev = 0; part[lev]; lev++) {
121 cur = merge(priv, cmp, part[lev], cur);
122 part[lev] = NULL;
123 }
124 if (lev > max_lev) {
125 if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
126 printk_once(KERN_DEBUG "list passed to"
127 " list_sort() too long for"
128 " efficiency\n");
129 lev--;
130 }
131 max_lev = lev;
132 }
133 part[lev] = cur;
134 }
135
136 for (lev = 0; lev < max_lev; lev++)
137 if (part[lev])
138 list = merge(priv, cmp, part[lev], list);
139
140 merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
141 }
142 EXPORT_SYMBOL(list_sort);
143
144 #ifdef CONFIG_TEST_LIST_SORT
145
146 #include <linux/random.h>
147
148 /*
149 * The pattern of set bits in the list length determines which cases
150 * are hit in list_sort().
151 */
152 #define TEST_LIST_LEN (512+128+2) /* not including head */
153
154 #define TEST_POISON1 0xDEADBEEF
155 #define TEST_POISON2 0xA324354C
156
157 struct debug_el {
158 unsigned int poison1;
159 struct list_head list;
160 unsigned int poison2;
161 int value;
162 unsigned serial;
163 };
164
165 /* Array, containing pointers to all elements in the test list */
166 static struct debug_el **elts __initdata;
167
check(struct debug_el * ela,struct debug_el * elb)168 static int __init check(struct debug_el *ela, struct debug_el *elb)
169 {
170 if (ela->serial >= TEST_LIST_LEN) {
171 printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
172 ela->serial);
173 return -EINVAL;
174 }
175 if (elb->serial >= TEST_LIST_LEN) {
176 printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
177 elb->serial);
178 return -EINVAL;
179 }
180 if (elts[ela->serial] != ela || elts[elb->serial] != elb) {
181 printk(KERN_ERR "list_sort_test: error: phantom element\n");
182 return -EINVAL;
183 }
184 if (ela->poison1 != TEST_POISON1 || ela->poison2 != TEST_POISON2) {
185 printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
186 ela->poison1, ela->poison2);
187 return -EINVAL;
188 }
189 if (elb->poison1 != TEST_POISON1 || elb->poison2 != TEST_POISON2) {
190 printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
191 elb->poison1, elb->poison2);
192 return -EINVAL;
193 }
194 return 0;
195 }
196
cmp(void * priv,struct list_head * a,struct list_head * b)197 static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
198 {
199 struct debug_el *ela, *elb;
200
201 ela = container_of(a, struct debug_el, list);
202 elb = container_of(b, struct debug_el, list);
203
204 check(ela, elb);
205 return ela->value - elb->value;
206 }
207
list_sort_test(void)208 static int __init list_sort_test(void)
209 {
210 int i, count = 1, err = -EINVAL;
211 struct debug_el *el;
212 struct list_head *cur, *tmp;
213 LIST_HEAD(head);
214
215 printk(KERN_DEBUG "list_sort_test: start testing list_sort()\n");
216
217 elts = kmalloc(sizeof(void *) * TEST_LIST_LEN, GFP_KERNEL);
218 if (!elts) {
219 printk(KERN_ERR "list_sort_test: error: cannot allocate "
220 "memory\n");
221 goto exit;
222 }
223
224 for (i = 0; i < TEST_LIST_LEN; i++) {
225 el = kmalloc(sizeof(*el), GFP_KERNEL);
226 if (!el) {
227 printk(KERN_ERR "list_sort_test: error: cannot "
228 "allocate memory\n");
229 goto exit;
230 }
231 /* force some equivalencies */
232 el->value = random32() % (TEST_LIST_LEN/3);
233 el->serial = i;
234 el->poison1 = TEST_POISON1;
235 el->poison2 = TEST_POISON2;
236 elts[i] = el;
237 list_add_tail(&el->list, &head);
238 }
239
240 list_sort(NULL, &head, cmp);
241
242 for (cur = head.next; cur->next != &head; cur = cur->next) {
243 struct debug_el *el1;
244 int cmp_result;
245
246 if (cur->next->prev != cur) {
247 printk(KERN_ERR "list_sort_test: error: list is "
248 "corrupted\n");
249 goto exit;
250 }
251
252 cmp_result = cmp(NULL, cur, cur->next);
253 if (cmp_result > 0) {
254 printk(KERN_ERR "list_sort_test: error: list is not "
255 "sorted\n");
256 goto exit;
257 }
258
259 el = container_of(cur, struct debug_el, list);
260 el1 = container_of(cur->next, struct debug_el, list);
261 if (cmp_result == 0 && el->serial >= el1->serial) {
262 printk(KERN_ERR "list_sort_test: error: order of "
263 "equivalent elements not preserved\n");
264 goto exit;
265 }
266
267 if (check(el, el1)) {
268 printk(KERN_ERR "list_sort_test: error: element check "
269 "failed\n");
270 goto exit;
271 }
272 count++;
273 }
274
275 if (count != TEST_LIST_LEN) {
276 printk(KERN_ERR "list_sort_test: error: bad list length %d",
277 count);
278 goto exit;
279 }
280
281 err = 0;
282 exit:
283 kfree(elts);
284 list_for_each_safe(cur, tmp, &head) {
285 list_del(cur);
286 kfree(container_of(cur, struct debug_el, list));
287 }
288 return err;
289 }
290 module_init(list_sort_test);
291 #endif /* CONFIG_TEST_LIST_SORT */
292