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 * The pattern of set bits in the list length determines which cases
150 * are hit in list_sort().
152 #define TEST_LIST_LEN (512+128+2) /* not including head */
154 #define TEST_POISON1 0xDEADBEEF
155 #define TEST_POISON2 0xA324354C
158 unsigned int poison1
;
159 struct list_head list
;
160 unsigned int poison2
;
165 /* Array, containing pointers to all elements in the test list */
166 static struct debug_el
**elts __initdata
;
168 static int __init
check(struct debug_el
*ela
, struct debug_el
*elb
)
170 if (ela
->serial
>= TEST_LIST_LEN
) {
171 printk(KERN_ERR
"list_sort_test: error: incorrect serial %d\n",
175 if (elb
->serial
>= TEST_LIST_LEN
) {
176 printk(KERN_ERR
"list_sort_test: error: incorrect serial %d\n",
180 if (elts
[ela
->serial
] != ela
|| elts
[elb
->serial
] != elb
) {
181 printk(KERN_ERR
"list_sort_test: error: phantom element\n");
184 if (ela
->poison1
!= TEST_POISON1
|| ela
->poison2
!= TEST_POISON2
) {
185 printk(KERN_ERR
"list_sort_test: error: bad poison: %#x/%#x\n",
186 ela
->poison1
, ela
->poison2
);
189 if (elb
->poison1
!= TEST_POISON1
|| elb
->poison2
!= TEST_POISON2
) {
190 printk(KERN_ERR
"list_sort_test: error: bad poison: %#x/%#x\n",
191 elb
->poison1
, elb
->poison2
);
197 static int __init
cmp(void *priv
, struct list_head
*a
, struct list_head
*b
)
199 struct debug_el
*ela
, *elb
;
201 ela
= container_of(a
, struct debug_el
, list
);
202 elb
= container_of(b
, struct debug_el
, list
);
205 return ela
->value
- elb
->value
;
208 static int __init
list_sort_test(void)
210 int i
, count
= 1, err
= -EINVAL
;
212 struct list_head
*cur
, *tmp
;
215 printk(KERN_DEBUG
"list_sort_test: start testing list_sort()\n");
217 elts
= kmalloc(sizeof(void *) * TEST_LIST_LEN
, GFP_KERNEL
);
219 printk(KERN_ERR
"list_sort_test: error: cannot allocate "
224 for (i
= 0; i
< TEST_LIST_LEN
; i
++) {
225 el
= kmalloc(sizeof(*el
), GFP_KERNEL
);
227 printk(KERN_ERR
"list_sort_test: error: cannot "
228 "allocate memory\n");
231 /* force some equivalencies */
232 el
->value
= random32() % (TEST_LIST_LEN
/3);
234 el
->poison1
= TEST_POISON1
;
235 el
->poison2
= TEST_POISON2
;
237 list_add_tail(&el
->list
, &head
);
240 list_sort(NULL
, &head
, cmp
);
242 for (cur
= head
.next
; cur
->next
!= &head
; cur
= cur
->next
) {
243 struct debug_el
*el1
;
246 if (cur
->next
->prev
!= cur
) {
247 printk(KERN_ERR
"list_sort_test: error: list is "
252 cmp_result
= cmp(NULL
, cur
, cur
->next
);
253 if (cmp_result
> 0) {
254 printk(KERN_ERR
"list_sort_test: error: list is not "
259 el
= container_of(cur
, struct debug_el
, list
);
260 el1
= container_of(cur
->next
, struct debug_el
, list
);
261 if (cmp_result
== 0 && el
->serial
>= el1
->serial
) {
262 printk(KERN_ERR
"list_sort_test: error: order of "
263 "equivalent elements not preserved\n");
267 if (check(el
, el1
)) {
268 printk(KERN_ERR
"list_sort_test: error: element check "
275 if (count
!= TEST_LIST_LEN
) {
276 printk(KERN_ERR
"list_sort_test: error: bad list length %d",
284 list_for_each_safe(cur
, tmp
, &head
) {
286 kfree(container_of(cur
, struct debug_el
, list
));
290 module_init(list_sort_test
);
291 #endif /* CONFIG_TEST_LIST_SORT */
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