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git.proxmox.com Git - mirror_ubuntu-artful-kernel.git/blob - lib/list_sort.c
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
);