146 строки
3.6 KiB
C
146 строки
3.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
#include <linux/kernel.h>
|
|
#include <linux/bug.h>
|
|
#include <linux/compiler.h>
|
|
#include <linux/export.h>
|
|
#include <linux/string.h>
|
|
#include <linux/list_sort.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;
|
|
u8 count = 0;
|
|
|
|
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.
|
|
*/
|
|
if (unlikely(!(++count)))
|
|
(*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 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);
|