include/list.h

   1 /*
   2  * Copyright (C) 2008 Karel Zak <kzak@redhat.com>
   3  * Copyright (C) 1999-2008 by Theodore Ts'o
   4  *
   5  * This file may be redistributed under the terms of the
   6  * GNU Lesser General Public License.
   7  *
   8  * (based on list.h from e2fsprogs)
   9  * Merge sort based on kernel's implementation.
  10  */
  11
  12 #ifndef UTIL_LINUX_LIST_H
  13 #define UTIL_LINUX_LIST_H
  14
  15 #include "c.h"
  16
  17 /* TODO: use AC_C_INLINE */
  18 #ifdef __GNUC__
  19 #define _INLINE_ static __inline__
  20 #else                         /* For Watcom C */
  21 #define _INLINE_ static inline
  22 #endif
  23
  24 /*
  25  * Simple doubly linked list implementation.
  26  *
  27  * Some of the internal functions ("__xxx") are useful when
  28  * manipulating whole lists rather than single entries, as
  29  * sometimes we already know the next/prev entries and we can
  30  * generate better code by using them directly rather than
  31  * using the generic single-entry routines.
  32  */
  33
  34 struct list_head {
  35         struct list_head *next, *prev;
  36 };
  37
  38 #define INIT_LIST_HEAD(ptr) do { \
  39         (ptr)->next = (ptr); (ptr)->prev = (ptr); \
  40 } while (0)
  41
  42 /*
  43  * Insert a new entry between two known consecutive entries.
  44  *
  45  * This is only for internal list manipulation where we know
  46  * the prev/next entries already!
  47  */
  48 _INLINE_ void __list_add(struct list_head * add,
  49         struct list_head * prev,
  50         struct list_head * next)
  51 {
  52         next->prev = add;
  53         add->next = next;
  54         add->prev = prev;
  55         prev->next = add;
  56 }
  57
  58 /**
  59  * list_add - add a new entry
  60  * @add:        new entry to be added
  61  * @head:       list head to add it after
  62  *
  63  * Insert a new entry after the specified head.
  64  * This is good for implementing stacks.
  65  */
  66 _INLINE_ void list_add(struct list_head *add, struct list_head *head)
  67 {
  68         __list_add(add, head, head->next);
  69 }
  70
  71 /**
  72  * list_add_tail - add a new entry
  73  * @add:        new entry to be added
  74  * @head:       list head to add it before
  75  *
  76  * Insert a new entry before the specified head.
  77  * This is useful for implementing queues.
  78  */
  79 _INLINE_ void list_add_tail(struct list_head *add, struct list_head *head)
  80 {
  81         __list_add(add, head->prev, head);
  82 }
  83
  84 /*
  85  * Delete a list entry by making the prev/next entries
  86  * point to each other.
  87  *
  88  * This is only for internal list manipulation where we know
  89  * the prev/next entries already!
  90  */
  91 _INLINE_ void __list_del(struct list_head * prev,
  92                                   struct list_head * next)
  93 {
  94         next->prev = prev;
  95         prev->next = next;
  96 }
  97
  98 /**
  99  * list_del - deletes entry from list.
 100  * @entry:      the element to delete from the list.
 101  *
 102  * list_empty() on @entry does not return true after this, @entry is
 103  * in an undefined state.
 104  */
 105 _INLINE_ void list_del(struct list_head *entry)
 106 {
 107         __list_del(entry->prev, entry->next);
 108 }
 109
 110 /**
 111  * list_del_init - deletes entry from list and reinitialize it.
 112  * @entry:      the element to delete from the list.
 113  */
 114 _INLINE_ void list_del_init(struct list_head *entry)
 115 {
 116         __list_del(entry->prev, entry->next);
 117         INIT_LIST_HEAD(entry);
 118 }
 119
 120 /**
 121  * list_empty - tests whether a list is empty
 122  * @head:       the list to test.
 123  */
 124 _INLINE_ int list_empty(struct list_head *head)
 125 {
 126         return head->next == head;
 127 }
 128
 129 /**
 130  * list_entry_is_last - tests whether is entry last in the list
 131  * @entry:      the entry to test.
 132  * @head:       the list to test.
 133  */
 134 _INLINE_ int list_entry_is_last(struct list_head *entry, struct list_head *head)
 135 {
 136         return head->prev == entry;
 137 }
 138
 139 /**
 140  * list_splice - join two lists
 141  * @list:       the new list to add.
 142  * @head:       the place to add it in the first list.
 143  */
 144 _INLINE_ void list_splice(struct list_head *list, struct list_head *head)
 145 {
 146         struct list_head *first = list->next;
 147
 148         if (first != list) {
 149                 struct list_head *last = list->prev;
 150                 struct list_head *at = head->next;
 151
 152                 first->prev = head;
 153                 head->next = first;
 154
 155                 last->next = at;
 156                 at->prev = last;
 157         }
 158 }
 159
 160 /**
 161  * list_entry - get the struct for this entry
 162  * @ptr:        the &struct list_head pointer.
 163  * @type:       the type of the struct this is embedded in.
 164  * @member:     the name of the list_struct within the struct.
 165  */
 166 #define list_entry(ptr, type, member)   container_of(ptr, type, member)
 167
 168 #define list_first_entry(head, type, member) \
 169         ((head) && (head)->next != (head) ? list_entry((head)->next, type, member) : NULL)
 170
 171 #define list_last_entry(head, type, member) \
 172         ((head) && (head)->prev != (head) ? list_entry((head)->prev, type, member) : NULL)
 173
 174 /**
 175  * list_for_each - iterate over elements in a list
 176  * @pos:        the &struct list_head to use as a loop counter.
 177  * @head:       the head for your list.
 178  */
 179 #define list_for_each(pos, head) \
 180         for (pos = (head)->next; pos != (head); pos = pos->next)
 181
 182 /**
 183  * list_for_each_backwardly - iterate over elements in a list in reverse
 184  * @pos:        the &struct list_head to use as a loop counter.
 185  * @head:       the head for your list.
 186  */
 187 #define list_for_each_backwardly(pos, head) \
 188         for (pos = (head)->prev; pos != (head); pos = pos->prev)
 189
 190 /**
 191  * list_for_each_safe - iterate over elements in a list, but don't dereference
 192  *                      pos after the body is done (in case it is freed)
 193  * @pos:        the &struct list_head to use as a loop counter.
 194  * @pnext:      the &struct list_head to use as a pointer to the next item.
 195  * @head:       the head for your list (not included in iteration).
 196  */
 197 #define list_for_each_safe(pos, pnext, head) \
 198         for (pos = (head)->next, pnext = pos->next; pos != (head); \
 199              pos = pnext, pnext = pos->next)
 200
 201 #define MAX_LIST_LENGTH_BITS 20
 202
 203 /*
 204  * Returns a list organized in an intermediate format suited
 205  * to chaining of merge() calls: null-terminated, no reserved or
 206  * sentinel head node, "prev" links not maintained.
 207  */
 208 _INLINE_ struct list_head *merge(int (*cmp)(struct list_head *a,
 209                                           struct list_head *b,
 210                                           void *data),
 211                                void *data,
 212                                struct list_head *a, struct list_head *b)
 213 {
 214         struct list_head head, *tail = &head;
 215
 216         while (a && b) {
 217                 /* if equal, take 'a' -- important for sort stability */
 218                 if ((*cmp)(a, b, data) <= 0) {
 219                         tail->next = a;
 220                         a = a->next;
 221                 } else {
 222                         tail->next = b;
 223                         b = b->next;
 224                 }
 225                 tail = tail->next;
 226         }
 227         tail->next = a ? a : b;
 228         return head.next;
 229 }
 230
 231 /*
 232  * Combine final list merge with restoration of standard doubly-linked
 233  * list structure.  This approach duplicates code from merge(), but
 234  * runs faster than the tidier alternatives of either a separate final
 235  * prev-link restoration pass, or maintaining the prev links
 236  * throughout.
 237  */
 238 _INLINE_ void merge_and_restore_back_links(int (*cmp)(struct list_head *a,
 239                                                     struct list_head *b,
 240                                                     void *data),
 241                                          void *data,
 242                                          struct list_head *head,
 243                                          struct list_head *a, struct list_head *b)
 244 {
 245         struct list_head *tail = head;
 246
 247         while (a && b) {
 248                 /* if equal, take 'a' -- important for sort stability */
 249                 if ((*cmp)(a, b, data) <= 0) {
 250                         tail->next = a;
 251                         a->prev = tail;
 252                         a = a->next;
 253                 } else {
 254                         tail->next = b;
 255                         b->prev = tail;
 256                         b = b->next;
 257                 }
 258                 tail = tail->next;
 259         }
 260         tail->next = a ? a : b;
 261
 262         do {
 263                 /*
 264                  * In worst cases this loop may run many iterations.
 265                  * Continue callbacks to the client even though no
 266                  * element comparison is needed, so the client's cmp()
 267                  * routine can invoke cond_resched() periodically.
 268                  */
 269                 (*cmp)(tail->next, tail->next, data);
 270
 271                 tail->next->prev = tail;
 272                 tail = tail->next;
 273         } while (tail->next);
 274
 275         tail->next = head;
 276         head->prev = tail;
 277 }
 278
 279
 280 /**
 281  * list_sort - sort a list
 282  * @head: the list to sort
 283  * @cmp: the elements comparison function
 284  *
 285  * This function implements "merge sort", which has O(nlog(n))
 286  * complexity.
 287  *
 288  * The comparison function @cmp must return a negative value if @a
 289  * should sort before @b, and a positive value if @a should sort after
 290  * @b. If @a and @b are equivalent, and their original relative
 291  * ordering is to be preserved, @cmp must return 0.
 292  */
 293 _INLINE_ void list_sort(struct list_head *head,
 294                         int (*cmp)(struct list_head *a,
 295                                    struct list_head *b,
 296                                    void *data),
 297                         void *data)
 298 {
 299         struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
 300                                                            -- last slot is a sentinel */
 301         size_t lev;  /* index into part[] */
 302         size_t max_lev = 0;
 303         struct list_head *list;
 304
 305         if (list_empty(head))
 306                 return;
 307
 308         memset(part, 0, sizeof(part));
 309
 310         head->prev->next = NULL;
 311         list = head->next;
 312
 313         while (list) {
 314                 struct list_head *cur = list;
 315                 list = list->next;
 316                 cur->next = NULL;
 317
 318                 for (lev = 0; part[lev]; lev++) {
 319                         cur = merge(cmp, data, part[lev], cur);
 320                         part[lev] = NULL;
 321                 }
 322                 if (lev > max_lev) {
 323                         /* list passed to list_sort() too long for efficiency */
 324                         if (lev >= ARRAY_SIZE(part) - 1)
 325                                 lev--;
 326                         max_lev = lev;
 327                 }
 328                 part[lev] = cur;
 329         }
 330
 331         for (lev = 0; lev < max_lev; lev++)
 332                 if (part[lev])
 333                         list = merge(cmp, data, part[lev], list);
 334
 335         merge_and_restore_back_links(cmp, data, head, part[max_lev], list);
 336 }
 337
 338 #undef _INLINE_
 339
 340 #endif /* UTIL_LINUX_LIST_H */