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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 | */ | |
f015ac3e | 73 | (*cmp)(priv, tail->next, tail->next); |
835cc0c8 DM |
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 | 83 | /** |
02b12b7a DM |
84 | * list_sort - sort a list |
85 | * @priv: private data, opaque to list_sort(), passed to @cmp | |
2c761270 DC |
86 | * @head: the list to sort |
87 | * @cmp: the elements comparison function | |
88 | * | |
02b12b7a DM |
89 | * This function implements "merge sort", which has O(nlog(n)) |
90 | * complexity. | |
2c761270 | 91 | * |
02b12b7a DM |
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. | |
2c761270 DC |
96 | */ |
97 | void list_sort(void *priv, struct list_head *head, | |
835cc0c8 DM |
98 | int (*cmp)(void *priv, struct list_head *a, |
99 | struct list_head *b)) | |
2c761270 | 100 | { |
835cc0c8 DM |
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; | |
2c761270 DC |
106 | |
107 | if (list_empty(head)) | |
108 | return; | |
109 | ||
835cc0c8 DM |
110 | memset(part, 0, sizeof(part)); |
111 | ||
112 | head->prev->next = NULL; | |
2c761270 | 113 | list = head->next; |
2c761270 | 114 | |
835cc0c8 DM |
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--; | |
2c761270 | 130 | } |
835cc0c8 | 131 | max_lev = lev; |
2c761270 | 132 | } |
835cc0c8 DM |
133 | part[lev] = cur; |
134 | } | |
2c761270 | 135 | |
835cc0c8 DM |
136 | for (lev = 0; lev < max_lev; lev++) |
137 | if (part[lev]) | |
138 | list = merge(priv, cmp, part[lev], list); | |
2c761270 | 139 | |
835cc0c8 DM |
140 | merge_and_restore_back_links(priv, cmp, head, part[max_lev], list); |
141 | } | |
142 | EXPORT_SYMBOL(list_sort); | |
2c761270 | 143 | |
835cc0c8 DM |
144 | #ifdef DEBUG_LIST_SORT |
145 | struct debug_el { | |
146 | struct list_head l_h; | |
147 | int value; | |
148 | unsigned serial; | |
149 | }; | |
2c761270 | 150 | |
835cc0c8 DM |
151 | static int cmp(void *priv, struct list_head *a, struct list_head *b) |
152 | { | |
153 | return container_of(a, struct debug_el, l_h)->value | |
154 | - container_of(b, struct debug_el, l_h)->value; | |
2c761270 DC |
155 | } |
156 | ||
835cc0c8 DM |
157 | /* |
158 | * The pattern of set bits in the list length determines which cases | |
159 | * are hit in list_sort(). | |
160 | */ | |
161 | #define LIST_SORT_TEST_LENGTH (512+128+2) /* not including head */ | |
162 | ||
163 | static int __init list_sort_test(void) | |
164 | { | |
165 | int i, r = 1, count; | |
166 | struct list_head *head = kmalloc(sizeof(*head), GFP_KERNEL); | |
167 | struct list_head *cur; | |
168 | ||
169 | printk(KERN_WARNING "testing list_sort()\n"); | |
170 | ||
171 | cur = head; | |
172 | for (i = 0; i < LIST_SORT_TEST_LENGTH; i++) { | |
173 | struct debug_el *el = kmalloc(sizeof(*el), GFP_KERNEL); | |
174 | BUG_ON(!el); | |
175 | /* force some equivalencies */ | |
176 | el->value = (r = (r * 725861) % 6599) % (LIST_SORT_TEST_LENGTH/3); | |
177 | el->serial = i; | |
178 | ||
179 | el->l_h.prev = cur; | |
180 | cur->next = &el->l_h; | |
181 | cur = cur->next; | |
182 | } | |
183 | head->prev = cur; | |
184 | ||
185 | list_sort(NULL, head, cmp); | |
186 | ||
187 | count = 1; | |
188 | for (cur = head->next; cur->next != head; cur = cur->next) { | |
189 | struct debug_el *el = container_of(cur, struct debug_el, l_h); | |
190 | int cmp_result = cmp(NULL, cur, cur->next); | |
191 | if (cur->next->prev != cur) { | |
192 | printk(KERN_EMERG "list_sort() returned " | |
193 | "a corrupted list!\n"); | |
194 | return 1; | |
195 | } else if (cmp_result > 0) { | |
196 | printk(KERN_EMERG "list_sort() failed to sort!\n"); | |
197 | return 1; | |
198 | } else if (cmp_result == 0 && | |
199 | el->serial >= container_of(cur->next, | |
200 | struct debug_el, l_h)->serial) { | |
201 | printk(KERN_EMERG "list_sort() failed to preserve order" | |
202 | " of equivalent elements!\n"); | |
203 | return 1; | |
204 | } | |
205 | kfree(cur->prev); | |
206 | count++; | |
207 | } | |
208 | kfree(cur); | |
209 | if (count != LIST_SORT_TEST_LENGTH) { | |
210 | printk(KERN_EMERG "list_sort() returned list of" | |
211 | "different length!\n"); | |
212 | return 1; | |
213 | } | |
214 | return 0; | |
215 | } | |
216 | module_init(list_sort_test); | |
217 | #endif |