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