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>
7 #define MAX_LIST_LENGTH_BITS 20
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.
14 static struct list_head *merge(void *priv,
15 int (*cmp)(void *priv, struct list_head *a,
17 struct list_head *a, struct list_head *b)
19 struct list_head head, *tail = &head;
22 /* if equal, take 'a' -- important for sort stability */
23 if ((*cmp)(priv, a, b) <= 0) {
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
43 static void merge_and_restore_back_links(void *priv,
44 int (*cmp)(void *priv, struct list_head *a,
46 struct list_head *head,
47 struct list_head *a, struct list_head *b)
49 struct list_head *tail = head;
52 /* if equal, take 'a' -- important for sort stability */
53 if ((*cmp)(priv, a, b) <= 0) {
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.
73 (*cmp)(priv, tail, tail);
75 tail->next->prev = tail;
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
89 * This function implements "merge sort" which has O(nlog(n)) complexity.
90 * The list is sorted in ascending order.
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.
96 void list_sort(void *priv, struct list_head *head,
97 int (*cmp)(void *priv, struct list_head *a,
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[] */
104 struct list_head *list;
106 if (list_empty(head))
109 memset(part, 0, sizeof(part));
111 head->prev->next = NULL;
115 struct list_head *cur = list;
119 for (lev = 0; part[lev]; lev++) {
120 cur = merge(priv, cmp, part[lev], cur);
124 if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
125 printk_once(KERN_DEBUG "list passed to"
126 " list_sort() too long for"
135 for (lev = 0; lev < max_lev; lev++)
137 list = merge(priv, cmp, part[lev], list);
139 merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
141 EXPORT_SYMBOL(list_sort);
143 #ifdef DEBUG_LIST_SORT
145 struct list_head l_h;
150 static int cmp(void *priv, struct list_head *a, struct list_head *b)
152 return container_of(a, struct debug_el, l_h)->value
153 - container_of(b, struct debug_el, l_h)->value;
157 * The pattern of set bits in the list length determines which cases
158 * are hit in list_sort().
160 #define LIST_SORT_TEST_LENGTH (512+128+2) /* not including head */
162 static int __init list_sort_test(void)
165 struct list_head *head = kmalloc(sizeof(*head), GFP_KERNEL);
166 struct list_head *cur;
168 printk(KERN_WARNING "testing list_sort()\n");
171 for (i = 0; i < LIST_SORT_TEST_LENGTH; i++) {
172 struct debug_el *el = kmalloc(sizeof(*el), GFP_KERNEL);
174 /* force some equivalencies */
175 el->value = (r = (r * 725861) % 6599) % (LIST_SORT_TEST_LENGTH/3);
179 cur->next = &el->l_h;
184 list_sort(NULL, head, cmp);
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");
194 } else if (cmp_result > 0) {
195 printk(KERN_EMERG "list_sort() failed to sort!\n");
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");
208 if (count != LIST_SORT_TEST_LENGTH) {
209 printk(KERN_EMERG "list_sort() returned list of"
210 "different length!\n");
215 module_init(list_sort_test);