Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 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 | |
Don Mullis | 835cc0c | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 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 | |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 83 | /** |
Don Mullis | 02b12b7 | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 84 | * list_sort - sort a list |
| 85 | * @priv: private data, opaque to list_sort(), passed to @cmp |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 86 | * @head: the list to sort |
| 87 | * @cmp: the elements comparison function |
| 88 | * |
Don Mullis | 02b12b7 | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 89 | * This function implements "merge sort", which has O(nlog(n)) |
| 90 | * complexity. |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 91 | * |
Don Mullis | 02b12b7 | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 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. |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 96 | */ |
| 97 | void list_sort(void *priv, struct list_head *head, |
Don Mullis | 835cc0c | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 98 | int (*cmp)(void *priv, struct list_head *a, |
| 99 | struct list_head *b)) |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 100 | { |
Don Mullis | 835cc0c | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 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; |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 106 | |
| 107 | if (list_empty(head)) |
| 108 | return; |
| 109 | |
Don Mullis | 835cc0c | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 110 | memset(part, 0, sizeof(part)); |
| 111 | |
| 112 | head->prev->next = NULL; |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 113 | list = head->next; |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 114 | |
Don Mullis | 835cc0c | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 115 | while (list) { |
| 116 | struct list_head *cur = list; |
| 117 | list = list->next; |
| 118 | cur->next = NULL; |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 119 | |
Don Mullis | 835cc0c | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 120 | for (lev = 0; part[lev]; lev++) { |
| 121 | cur = merge(priv, cmp, part[lev], cur); |
| 122 | part[lev] = NULL; |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 123 | } |
Don Mullis | 835cc0c | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 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; |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 134 | } |
| 135 | |
Don Mullis | 835cc0c | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 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 DEBUG_LIST_SORT |
| 145 | struct debug_el { |
| 146 | struct list_head l_h; |
| 147 | int value; |
| 148 | unsigned serial; |
| 149 | }; |
| 150 | |
| 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; |
Dave Chinner | 2c76127 | 2010-01-12 17:39:16 +1100 | [diff] [blame] | 155 | } |
| 156 | |
Don Mullis | 835cc0c | 2010-03-05 13:43:15 -0800 | [diff] [blame] | 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 |