Re: [PATCH] sort: Introduce generic list_sort function

[Artem Bityutskiy <dedekind@infradead.org>]

On Tue, 2010-01-05 at 10:54 +1100, Dave Chinner wrote:
> 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.
> 
> CC: Dave Airlie <airlied@redhat.com>
> CC: Artem Bityutskiy <dedekind@infradead.org>
> CC: Adrian Hunter <adrian.hunter@nokia.com>
> 
> Signed-off-by: Dave Chinner <david@fromorbit.com>
> ---
>  drivers/gpu/drm/drm_modes.c |   90 ++--------------------------------------
>  fs/ubifs/gc.c               |   95 ------------------------------------------
>  include/linux/sort.h        |    5 ++
>  lib/sort.c                  |   97 +++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 106 insertions(+), 181 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index 51f6772..3846ed4 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -1,9 +1,4 @@
>  /*
> - * The list_sort function is (presumably) licensed under the GPL (see the
> - * top level "COPYING" file for details).
> - *
> - * The remainder of this file is:
> - *
>   * Copyright © 1997-2003 by The XFree86 Project, Inc.
>   * Copyright © 2007 Dave Airlie
>   * Copyright © 2007-2008 Intel Corporation
> @@ -36,6 +31,7 @@
>   */
>  
>  #include <linux/list.h>
> +#include <linux/sort.h>
>  #include "drmP.h"
>  #include "drm.h"
>  #include "drm_crtc.h"
> @@ -829,6 +825,7 @@ EXPORT_SYMBOL(drm_mode_prune_invalid);
>  
>  /**
>   * drm_mode_compare - compare modes for favorability
> + * @priv: unused
>   * @lh_a: list_head for first mode
>   * @lh_b: list_head for second mode
>   *
> @@ -842,7 +839,7 @@ EXPORT_SYMBOL(drm_mode_prune_invalid);
>   * Negative if @lh_a is better than @lh_b, zero if they're equivalent, or
>   * positive if @lh_b is better than @lh_a.
>   */
> -static int drm_mode_compare(struct list_head *lh_a, struct list_head *lh_b)
> +static int drm_mode_compare(void *priv, struct list_head *lh_a, struct list_head *lh_b)
>  {
>  	struct drm_display_mode *a = list_entry(lh_a, struct drm_display_mode, head);
>  	struct drm_display_mode *b = list_entry(lh_b, struct drm_display_mode, head);
> @@ -859,85 +856,6 @@ static int drm_mode_compare(struct list_head *lh_a, struct list_head *lh_b)
>  	return diff;
>  }
>  
> -/* FIXME: what we don't have a list sort function? */
> -/* list sort from Mark J Roberts (mjr@znex.org) */
> -void list_sort(struct list_head *head,
> -	       int (*cmp)(struct list_head *a, struct list_head *b))
> -{
> -	struct list_head *p, *q, *e, *list, *tail, *oldhead;
> -	int insize, nmerges, psize, qsize, i;
> -
> -	list = head->next;
> -	list_del(head);
> -	insize = 1;
> -	for (;;) {
> -		p = oldhead = list;
> -		list = tail = NULL;
> -		nmerges = 0;
> -
> -		while (p) {
> -			nmerges++;
> -			q = p;
> -			psize = 0;
> -			for (i = 0; i < insize; i++) {
> -				psize++;
> -				q = q->next == oldhead ? NULL : q->next;
> -				if (!q)
> -					break;
> -			}
> -
> -			qsize = insize;
> -			while (psize > 0 || (qsize > 0 && q)) {
> -				if (!psize) {
> -					e = q;
> -					q = q->next;
> -					qsize--;
> -					if (q == oldhead)
> -						q = NULL;
> -				} else if (!qsize || !q) {
> -					e = p;
> -					p = p->next;
> -					psize--;
> -					if (p == oldhead)
> -						p = NULL;
> -				} else if (cmp(p, q) <= 0) {
> -					e = p;
> -					p = p->next;
> -					psize--;
> -					if (p == oldhead)
> -						p = NULL;
> -				} else {
> -					e = q;
> -					q = q->next;
> -					qsize--;
> -					if (q == oldhead)
> -						q = NULL;
> -				}
> -				if (tail)
> -					tail->next = e;
> -				else
> -					list = e;
> -				e->prev = tail;
> -				tail = e;
> -			}
> -			p = q;
> -		}
> -
> -		tail->next = list;
> -		list->prev = tail;
> -
> -		if (nmerges <= 1)
> -			break;
> -
> -		insize *= 2;
> -	}
> -
> -	head->next = list;
> -	head->prev = list->prev;
> -	list->prev->next = head;
> -	list->prev = head;
> -}
> -
>  /**
>   * drm_mode_sort - sort mode list
>   * @mode_list: list to sort
> @@ -949,7 +867,7 @@ void list_sort(struct list_head *head,
>   */
>  void drm_mode_sort(struct list_head *mode_list)
>  {
> -	list_sort(mode_list, drm_mode_compare);
> +	list_sort(NULL, mode_list, drm_mode_compare);
>  }
>  EXPORT_SYMBOL(drm_mode_sort);
>  
> diff --git a/fs/ubifs/gc.c b/fs/ubifs/gc.c
> index 618c270..4976e07 100644
> --- a/fs/ubifs/gc.c
> +++ b/fs/ubifs/gc.c
> @@ -108,101 +108,6 @@ static int switch_gc_head(struct ubifs_info *c)
>  }
>  
>  /**
> - * list_sort - sort a list.
> - * @priv: private data, passed to @cmp
> - * @head: the list to sort
> - * @cmp: the elements comparison function
> - *
> - * This function has been implemented by Mark J Roberts <mjr@znex.org>. It
> - * implements "merge sort" which has O(nlog(n)) complexity. The list is sorted
> - * in ascending order.
> - *
> - * The comparison function @cmp is supposed to return a negative value if @a is
> - * than @b, and a positive value if @a is greater than @b. If @a and @b are
> - * equivalent, then it does not matter what this function returns.
> - */
> -static void list_sort(void *priv, struct list_head *head,
> -		      int (*cmp)(void *priv, struct list_head *a,
> -				 struct list_head *b))
> -{
> -	struct list_head *p, *q, *e, *list, *tail, *oldhead;
> -	int insize, nmerges, psize, qsize, i;
> -
> -	if (list_empty(head))
> -		return;
> -
> -	list = head->next;
> -	list_del(head);
> -	insize = 1;
> -	for (;;) {
> -		p = oldhead = list;
> -		list = tail = NULL;
> -		nmerges = 0;
> -
> -		while (p) {
> -			nmerges++;
> -			q = p;
> -			psize = 0;
> -			for (i = 0; i < insize; i++) {
> -				psize++;
> -				q = q->next == oldhead ? NULL : q->next;
> -				if (!q)
> -					break;
> -			}
> -
> -			qsize = insize;
> -			while (psize > 0 || (qsize > 0 && q)) {
> -				if (!psize) {
> -					e = q;
> -					q = q->next;
> -					qsize--;
> -					if (q == oldhead)
> -						q = NULL;
> -				} else if (!qsize || !q) {
> -					e = p;
> -					p = p->next;
> -					psize--;
> -					if (p == oldhead)
> -						p = NULL;
> -				} else if (cmp(priv, p, q) <= 0) {
> -					e = p;
> -					p = p->next;
> -					psize--;
> -					if (p == oldhead)
> -						p = NULL;
> -				} else {
> -					e = q;
> -					q = q->next;
> -					qsize--;
> -					if (q == oldhead)
> -						q = NULL;
> -				}
> -				if (tail)
> -					tail->next = e;
> -				else
> -					list = e;
> -				e->prev = tail;
> -				tail = e;
> -			}
> -			p = q;
> -		}
> -
> -		tail->next = list;
> -		list->prev = tail;
> -
> -		if (nmerges <= 1)
> -			break;
> -
> -		insize *= 2;
> -	}
> -
> -	head->next = list;
> -	head->prev = list->prev;
> -	list->prev->next = head;
> -	list->prev = head;
> -}
> -
> -/**
>   * data_nodes_cmp - compare 2 data nodes.
>   * @priv: UBIFS file-system description object
>   * @a: first data node
> diff --git a/include/linux/sort.h b/include/linux/sort.h
> index d534da2..99a2ed5 100644
> --- a/include/linux/sort.h
> +++ b/include/linux/sort.h
> @@ -3,8 +3,13 @@
>  
>  #include <linux/types.h>
>  
> +struct list_head;
> +
>  void sort(void *base, size_t num, size_t size,
>  	  int (*cmp)(const void *, const void *),
>  	  void (*swap)(void *, void *, int));
>  
> +void list_sort(void *priv, struct list_head *head,
> +	       int (*cmp)(void *priv, struct list_head *a,
> +			  struct list_head *b));
>  #endif
> diff --git a/lib/sort.c b/lib/sort.c
> index 926d004..1772c45 100644
> --- a/lib/sort.c
> +++ b/lib/sort.c
> @@ -8,6 +8,7 @@
>  #include <linux/module.h>
>  #include <linux/sort.h>
>  #include <linux/slab.h>
> +#include <linux/list.h>
>  
>  static void u32_swap(void *a, void *b, int size)
>  {
> @@ -121,3 +122,99 @@ static int sort_test(void)
>  
>  module_init(sort_test);
>  #endif
> +
> +/**
> + * list_sort - sort a list.
> + * @priv: private data, passed to @cmp
> + * @head: the list to sort
> + * @cmp: the elements comparison function
> + *
> + * This function has been implemented by Mark J Roberts <mjr@znex.org>. It
> + * implements "merge sort" which has O(nlog(n)) complexity. The list is sorted
> + * in ascending order.
> + *
> + * The comparison function @cmp is supposed to return a negative value if @a is
> + * than @b, and a positive value if @a is greater than @b. If @a and @b are

While you are on it, could you also please fix the typo: "if @a is less
than @b".

> + * equivalent, then it does not matter what this function returns.
> + */

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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