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2c761270 DC |
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 | ||
835cc0c8 DM |
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 | */ | |
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 | */ | |
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, tail); | |
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 | ||
2c761270 DC |
83 | /** |
84 | * list_sort - sort a list. | |
85 | * @priv: private data, passed to @cmp | |
86 | * @head: the list to sort | |
87 | * @cmp: the elements comparison function | |
88 | * | |
835cc0c8 DM |
89 | * This function implements "merge sort" which has O(nlog(n)) complexity. |
90 | * The list is sorted in ascending order. | |
2c761270 DC |
91 | * |
92 | * The comparison function @cmp is supposed to return a negative value if @a is | |
93 | * less than @b, and a positive value if @a is greater than @b. If @a and @b | |
94 | * are equivalent, then it does not matter what this function returns. | |
95 | */ | |
96 | void list_sort(void *priv, struct list_head *head, | |
835cc0c8 DM |
97 | int (*cmp)(void *priv, struct list_head *a, |
98 | struct list_head *b)) | |
2c761270 | 99 | { |
835cc0c8 DM |
100 | struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists |
101 | -- last slot is a sentinel */ | |
102 | int lev; /* index into part[] */ | |
103 | int max_lev = 0; | |
104 | struct list_head *list; | |
2c761270 DC |
105 | |
106 | if (list_empty(head)) | |
107 | return; | |
108 | ||
835cc0c8 DM |
109 | memset(part, 0, sizeof(part)); |
110 | ||
111 | head->prev->next = NULL; | |
2c761270 | 112 | list = head->next; |
2c761270 | 113 | |
835cc0c8 DM |
114 | while (list) { |
115 | struct list_head *cur = list; | |
116 | list = list->next; | |
117 | cur->next = NULL; | |
118 | ||
119 | for (lev = 0; part[lev]; lev++) { | |
120 | cur = merge(priv, cmp, part[lev], cur); | |
121 | part[lev] = NULL; | |
122 | } | |
123 | if (lev > max_lev) { | |
124 | if (unlikely(lev >= ARRAY_SIZE(part)-1)) { | |
125 | printk_once(KERN_DEBUG "list passed to" | |
126 | " list_sort() too long for" | |
127 | " efficiency\n"); | |
128 | lev--; | |
2c761270 | 129 | } |
835cc0c8 | 130 | max_lev = lev; |
2c761270 | 131 | } |
835cc0c8 DM |
132 | part[lev] = cur; |
133 | } | |
2c761270 | 134 | |
835cc0c8 DM |
135 | for (lev = 0; lev < max_lev; lev++) |
136 | if (part[lev]) | |
137 | list = merge(priv, cmp, part[lev], list); | |
2c761270 | 138 | |
835cc0c8 DM |
139 | merge_and_restore_back_links(priv, cmp, head, part[max_lev], list); |
140 | } | |
141 | EXPORT_SYMBOL(list_sort); | |
2c761270 | 142 | |
835cc0c8 DM |
143 | #ifdef DEBUG_LIST_SORT |
144 | struct debug_el { | |
145 | struct list_head l_h; | |
146 | int value; | |
147 | unsigned serial; | |
148 | }; | |
2c761270 | 149 | |
835cc0c8 DM |
150 | static int cmp(void *priv, struct list_head *a, struct list_head *b) |
151 | { | |
152 | return container_of(a, struct debug_el, l_h)->value | |
153 | - container_of(b, struct debug_el, l_h)->value; | |
2c761270 DC |
154 | } |
155 | ||
835cc0c8 DM |
156 | /* |
157 | * The pattern of set bits in the list length determines which cases | |
158 | * are hit in list_sort(). | |
159 | */ | |
160 | #define LIST_SORT_TEST_LENGTH (512+128+2) /* not including head */ | |
161 | ||
162 | static int __init list_sort_test(void) | |
163 | { | |
164 | int i, r = 1, count; | |
165 | struct list_head *head = kmalloc(sizeof(*head), GFP_KERNEL); | |
166 | struct list_head *cur; | |
167 | ||
168 | printk(KERN_WARNING "testing list_sort()\n"); | |
169 | ||
170 | cur = head; | |
171 | for (i = 0; i < LIST_SORT_TEST_LENGTH; i++) { | |
172 | struct debug_el *el = kmalloc(sizeof(*el), GFP_KERNEL); | |
173 | BUG_ON(!el); | |
174 | /* force some equivalencies */ | |
175 | el->value = (r = (r * 725861) % 6599) % (LIST_SORT_TEST_LENGTH/3); | |
176 | el->serial = i; | |
177 | ||
178 | el->l_h.prev = cur; | |
179 | cur->next = &el->l_h; | |
180 | cur = cur->next; | |
181 | } | |
182 | head->prev = cur; | |
183 | ||
184 | list_sort(NULL, head, cmp); | |
185 | ||
186 | count = 1; | |
187 | for (cur = head->next; cur->next != head; cur = cur->next) { | |
188 | struct debug_el *el = container_of(cur, struct debug_el, l_h); | |
189 | int cmp_result = cmp(NULL, cur, cur->next); | |
190 | if (cur->next->prev != cur) { | |
191 | printk(KERN_EMERG "list_sort() returned " | |
192 | "a corrupted list!\n"); | |
193 | return 1; | |
194 | } else if (cmp_result > 0) { | |
195 | printk(KERN_EMERG "list_sort() failed to sort!\n"); | |
196 | return 1; | |
197 | } else if (cmp_result == 0 && | |
198 | el->serial >= container_of(cur->next, | |
199 | struct debug_el, l_h)->serial) { | |
200 | printk(KERN_EMERG "list_sort() failed to preserve order" | |
201 | " of equivalent elements!\n"); | |
202 | return 1; | |
203 | } | |
204 | kfree(cur->prev); | |
205 | count++; | |
206 | } | |
207 | kfree(cur); | |
208 | if (count != LIST_SORT_TEST_LENGTH) { | |
209 | printk(KERN_EMERG "list_sort() returned list of" | |
210 | "different length!\n"); | |
211 | return 1; | |
212 | } | |
213 | return 0; | |
214 | } | |
215 | module_init(list_sort_test); | |
216 | #endif |