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git.proxmox.com Git - mirror_ubuntu-eoan-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, 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 DEBUG_LIST_SORT
146 struct list_head l_h
;
151 static int cmp(void *priv
, struct list_head
*a
, struct list_head
*b
)
153 return container_of(a
, struct debug_el
, l_h
)->value
154 - container_of(b
, struct debug_el
, l_h
)->value
;
158 * The pattern of set bits in the list length determines which cases
159 * are hit in list_sort().
161 #define LIST_SORT_TEST_LENGTH (512+128+2) /* not including head */
163 static int __init
list_sort_test(void)
166 struct list_head
*head
= kmalloc(sizeof(*head
), GFP_KERNEL
);
167 struct list_head
*cur
;
169 printk(KERN_WARNING
"testing list_sort()\n");
172 for (i
= 0; i
< LIST_SORT_TEST_LENGTH
; i
++) {
173 struct debug_el
*el
= kmalloc(sizeof(*el
), GFP_KERNEL
);
175 /* force some equivalencies */
176 el
->value
= (r
= (r
* 725861) % 6599) % (LIST_SORT_TEST_LENGTH
/3);
180 cur
->next
= &el
->l_h
;
185 list_sort(NULL
, head
, cmp
);
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");
195 } else if (cmp_result
> 0) {
196 printk(KERN_EMERG
"list_sort() failed to sort!\n");
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");
209 if (count
!= LIST_SORT_TEST_LENGTH
) {
210 printk(KERN_EMERG
"list_sort() returned list of"
211 "different length!\n");
216 module_init(list_sort_test
);