#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);