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
->next
, tail
->next
);
75 tail
->next
->prev
= tail
;
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
89 * This function implements "merge sort", which has O(nlog(n))
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.
97 void list_sort(void *priv
, struct list_head
*head
,
98 int (*cmp
)(void *priv
, struct list_head
*a
,
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[] */
105 struct list_head
*list
;
107 if (list_empty(head
))
110 memset(part
, 0, sizeof(part
));
112 head
->prev
->next
= NULL
;
116 struct list_head
*cur
= list
;
120 for (lev
= 0; part
[lev
]; lev
++) {
121 cur
= merge(priv
, cmp
, part
[lev
], cur
);
125 if (unlikely(lev
>= ARRAY_SIZE(part
)-1)) {
126 printk_once(KERN_DEBUG
"list passed to"
127 " list_sort() too long for"
136 for (lev
= 0; lev
< max_lev
; lev
++)
138 list
= merge(priv
, cmp
, part
[lev
], list
);
140 merge_and_restore_back_links(priv
, cmp
, head
, part
[max_lev
], list
);
142 EXPORT_SYMBOL(list_sort
);
144 #ifdef CONFIG_TEST_LIST_SORT
146 #include <linux/random.h>
149 struct list_head list
;
154 static int cmp(void *priv
, struct list_head
*a
, struct list_head
*b
)
156 return container_of(a
, struct debug_el
, list
)->value
157 - container_of(b
, struct debug_el
, list
)->value
;
161 * The pattern of set bits in the list length determines which cases
162 * are hit in list_sort().
164 #define TEST_LIST_LEN (512+128+2) /* not including head */
166 static int __init
list_sort_test(void)
169 struct list_head
*head
= kmalloc(sizeof(*head
), GFP_KERNEL
);
170 struct list_head
*cur
;
172 printk(KERN_DEBUG
"testing list_sort()\n");
175 for (i
= 0; i
< TEST_LIST_LEN
; i
++) {
176 struct debug_el
*el
= kmalloc(sizeof(*el
), GFP_KERNEL
);
178 /* force some equivalencies */
179 el
->value
= random32() % (TEST_LIST_LEN
/3);
183 cur
->next
= &el
->list
;
188 list_sort(NULL
, head
, cmp
);
191 for (cur
= head
->next
; cur
->next
!= head
; cur
= cur
->next
) {
192 struct debug_el
*el
= container_of(cur
, struct debug_el
, list
);
193 int cmp_result
= cmp(NULL
, cur
, cur
->next
);
194 if (cur
->next
->prev
!= cur
) {
195 printk(KERN_ERR
"list_sort() returned "
196 "a corrupted list!\n");
198 } else if (cmp_result
> 0) {
199 printk(KERN_ERR
"list_sort() failed to sort!\n");
201 } else if (cmp_result
== 0 &&
202 el
->serial
>= container_of(cur
->next
,
203 struct debug_el
, list
)->serial
) {
204 printk(KERN_ERR
"list_sort() failed to preserve order "
205 "of equivalent elements!\n");
212 if (count
!= TEST_LIST_LEN
) {
213 printk(KERN_ERR
"list_sort() returned list of "
214 "different length!\n");
219 module_init(list_sort_test
);
220 #endif /* CONFIG_TEST_LIST_SORT */