2c761270d5
There are two copies of list_sort() in the tree already, one in the DRM code, another in ubifs. Now XFS needs this as well. Create a generic list_sort() function from the ubifs version and convert existing users to it so we don't end up with yet another copy in the tree. Signed-off-by: Dave Chinner <david@fromorbit.com> Acked-by: Dave Airlie <airlied@redhat.com> Acked-by: Artem Bityutskiy <dedekind@infradead.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
103 lines
2.0 KiB
C
103 lines
2.0 KiB
C
#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/list_sort.h>
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#include <linux/slab.h>
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#include <linux/list.h>
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/**
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* list_sort - sort a list.
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* @priv: private data, passed to @cmp
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* @head: the list to sort
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* @cmp: the elements comparison function
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*
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* This function has been implemented by Mark J Roberts <mjr@znex.org>. It
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* implements "merge sort" which has O(nlog(n)) complexity. The list is sorted
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* in ascending order.
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*
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* The comparison function @cmp is supposed to return a negative value if @a is
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* less than @b, and a positive value if @a is greater than @b. If @a and @b
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* are equivalent, then it does not matter what this function returns.
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*/
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void list_sort(void *priv, struct list_head *head,
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int (*cmp)(void *priv, struct list_head *a,
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struct list_head *b))
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{
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struct list_head *p, *q, *e, *list, *tail, *oldhead;
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int insize, nmerges, psize, qsize, i;
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if (list_empty(head))
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return;
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list = head->next;
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list_del(head);
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insize = 1;
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for (;;) {
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p = oldhead = list;
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list = tail = NULL;
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nmerges = 0;
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while (p) {
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nmerges++;
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q = p;
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psize = 0;
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for (i = 0; i < insize; i++) {
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psize++;
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q = q->next == oldhead ? NULL : q->next;
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if (!q)
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break;
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}
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qsize = insize;
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while (psize > 0 || (qsize > 0 && q)) {
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if (!psize) {
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e = q;
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q = q->next;
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qsize--;
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if (q == oldhead)
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q = NULL;
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} else if (!qsize || !q) {
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e = p;
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p = p->next;
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psize--;
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if (p == oldhead)
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p = NULL;
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} else if (cmp(priv, p, q) <= 0) {
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e = p;
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p = p->next;
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psize--;
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if (p == oldhead)
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p = NULL;
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} else {
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e = q;
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q = q->next;
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qsize--;
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if (q == oldhead)
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q = NULL;
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}
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if (tail)
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tail->next = e;
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else
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list = e;
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e->prev = tail;
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tail = e;
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}
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p = q;
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}
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tail->next = list;
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list->prev = tail;
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if (nmerges <= 1)
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break;
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insize *= 2;
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}
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head->next = list;
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head->prev = list->prev;
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list->prev->next = head;
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list->prev = head;
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}
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EXPORT_SYMBOL(list_sort);
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