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#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/list_sort.h>
#include <linux/slab.h>
#include <linux/list.h>
#define MAX_LIST_LENGTH_BITS 20
/*
* Returns a list organized in an intermediate format suited
* to chaining of merge() calls: null-terminated, no reserved or
* sentinel head node, "prev" links not maintained.
*/
static struct list_head *merge(void *priv,
int (*cmp)(void *priv, struct list_head *a,
struct list_head *b),
struct list_head *a, struct list_head *b)
{
struct list_head head, *tail = &head;
while (a && b) {
/* if equal, take 'a' -- important for sort stability */
if ((*cmp)(priv, a, b) <= 0) {
tail->next = a;
a = a->next;
} else {
tail->next = b;
b = b->next;
}
tail = tail->next;
}
tail->next = a?:b;
return head.next;
}
/*
* Combine final list merge with restoration of standard doubly-linked
* list structure. This approach duplicates code from merge(), but
* runs faster than the tidier alternatives of either a separate final
* prev-link restoration pass, or maintaining the prev links
* throughout.
*/
static void merge_and_restore_back_links(void *priv,
int (*cmp)(void *priv, struct list_head *a,
struct list_head *b),
struct list_head *head,
struct list_head *a, struct list_head *b)
{
struct list_head *tail = head;
while (a && b) {
/* if equal, take 'a' -- important for sort stability */
if ((*cmp)(priv, a, b) <= 0) {
tail->next = a;
a->prev = tail;
a = a->next;
} else {
tail->next = b;
b->prev = tail;
b = b->next;
}
tail = tail->next;
}
tail->next = a ? : b;
do {
/*
* In worst cases this loop may run many iterations.
* Continue callbacks to the client even though no
* element comparison is needed, so the client's cmp()
* routine can invoke cond_resched() periodically.
*/
(*cmp)(priv, tail->next, tail->next);
tail->next->prev = tail;
tail = tail->next;
} while (tail->next);
tail->next = head;
head->prev = tail;
}
/**
* list_sort - sort a list
* @priv: private data, opaque to list_sort(), passed to @cmp
* @head: the list to sort
* @cmp: the elements comparison function
*
* This function implements "merge sort", which has O(nlog(n))
* complexity.
*
* The comparison function @cmp must return a negative value if @a
* should sort before @b, and a positive value if @a should sort after
* @b. If @a and @b are equivalent, and their original relative
* ordering is to be preserved, @cmp must return 0.
*/
void list_sort(void *priv, struct list_head *head,
int (*cmp)(void *priv, struct list_head *a,
struct list_head *b))
{
struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
-- last slot is a sentinel */
int lev; /* index into part[] */
int max_lev = 0;
struct list_head *list;
if (list_empty(head))
return;
memset(part, 0, sizeof(part));
head->prev->next = NULL;
list = head->next;
while (list) {
struct list_head *cur = list;
list = list->next;
cur->next = NULL;
for (lev = 0; part[lev]; lev++) {
cur = merge(priv, cmp, part[lev], cur);
part[lev] = NULL;
}
if (lev > max_lev) {
if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
printk_once(KERN_DEBUG "list passed to"
" list_sort() too long for"
" efficiency\n");
lev--;
}
max_lev = lev;
}
part[lev] = cur;
}
for (lev = 0; lev < max_lev; lev++)
if (part[lev])
list = merge(priv, cmp, part[lev], list);
merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
}
EXPORT_SYMBOL(list_sort);
#ifdef CONFIG_TEST_LIST_SORT
#include <linux/random.h>
struct debug_el {
struct list_head list;
int value;
unsigned serial;
};
static int cmp(void *priv, struct list_head *a, struct list_head *b)
{
return container_of(a, struct debug_el, list)->value
- container_of(b, struct debug_el, list)->value;
}
/*
* The pattern of set bits in the list length determines which cases
* are hit in list_sort().
*/
#define TEST_LIST_LEN (512+128+2) /* not including head */
static int __init list_sort_test(void)
{
int i, count = 1, err = -EINVAL;
struct debug_el *el;
struct list_head *cur, *tmp;
LIST_HEAD(head);
printk(KERN_DEBUG "list_sort_test: start testing list_sort()\n");
for (i = 0; i < TEST_LIST_LEN; i++) {
el = kmalloc(sizeof(*el), GFP_KERNEL);
if (!el) {
printk(KERN_ERR "list_sort_test: error: cannot "
"allocate memory\n");
goto exit;
}
/* force some equivalencies */
el->value = random32() % (TEST_LIST_LEN/3);
el->serial = i;
list_add_tail(&el->list, &head);
}
list_sort(NULL, &head, cmp);
for (cur = head.next; cur->next != &head; cur = cur->next) {
struct debug_el *el1;
int cmp_result;
if (cur->next->prev != cur) {
printk(KERN_ERR "list_sort_test: error: list is "
"corrupted\n");
goto exit;
}
cmp_result = cmp(NULL, cur, cur->next);
if (cmp_result > 0) {
printk(KERN_ERR "list_sort_test: error: list is not "
"sorted\n");
goto exit;
}
el = container_of(cur, struct debug_el, list);
el1 = container_of(cur->next, struct debug_el, list);
if (cmp_result == 0 && el->serial >= el1->serial) {
printk(KERN_ERR "list_sort_test: error: order of "
"equivalent elements not preserved\n");
goto exit;
}
count++;
}
if (count != TEST_LIST_LEN) {
printk(KERN_ERR "list_sort_test: error: bad list length %d",
count);
goto exit;
}
err = 0;
exit:
list_for_each_safe(cur, tmp, &head) {
list_del(cur);
kfree(container_of(cur, struct debug_el, list));
}
return err;
}
module_init(list_sort_test);
#endif /* CONFIG_TEST_LIST_SORT */
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