include/linux/list_nulls.h

   1 #ifndef _LINUX_LIST_NULLS_H
   2 #define _LINUX_LIST_NULLS_H
   3
   4 /*
   5  * Special version of lists, where end of list is not a NULL pointer,
   6  * but a 'nulls' marker, which can have many different values.
   7  * (up to 2^31 different values guaranteed on all platforms)
   8  *
   9  * In the standard hlist, termination of a list is the NULL pointer.
  10  * In this special 'nulls' variant, we use the fact that objects stored in
  11  * a list are aligned on a word (4 or 8 bytes alignment).
  12  * We therefore use the last significant bit of 'ptr' :
  13  * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
  14  * Set to 0 : This is a pointer to some object (ptr)
  15  */
  16
  17 struct hlist_nulls_head {
  18         struct hlist_nulls_node *first;
  19 };
  20
  21 struct hlist_nulls_node {
  22         struct hlist_nulls_node *next, **pprev;
  23 };
  24 #define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
  25         ((ptr)->first = (struct hlist_nulls_node *) (1UL | (((long)nulls) << 1)))
  26
  27 #define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
  28 /**
  29  * ptr_is_a_nulls - Test if a ptr is a nulls
  30  * @ptr: ptr to be tested
  31  *
  32  */
  33 static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
  34 {
  35         return ((unsigned long)ptr & 1);
  36 }
  37
  38 /**
  39  * get_nulls_value - Get the 'nulls' value of the end of chain
  40  * @ptr: end of chain
  41  *
  42  * Should be called only if is_a_nulls(ptr);
  43  */
  44 static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
  45 {
  46         return ((unsigned long)ptr) >> 1;
  47 }
  48
  49 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
  50 {
  51         return !h->pprev;
  52 }
  53
  54 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
  55 {
  56         return is_a_nulls(h->first);
  57 }
  58
  59 static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
  60 {
  61         struct hlist_nulls_node *next = n->next;
  62         struct hlist_nulls_node **pprev = n->pprev;
  63         *pprev = next;
  64         if (!is_a_nulls(next))
  65                 next->pprev = pprev;
  66 }
  67
  68 /**
  69  * hlist_nulls_for_each_entry   - iterate over list of given type
  70  * @tpos:       the type * to use as a loop cursor.
  71  * @pos:        the &struct hlist_node to use as a loop cursor.
  72  * @head:       the head for your list.
  73  * @member:     the name of the hlist_node within the struct.
  74  *
  75  */
  76 #define hlist_nulls_for_each_entry(tpos, pos, head, member)                    \
  77         for (pos = (head)->first;                                              \
  78              (!is_a_nulls(pos)) &&                                             \
  79                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
  80              pos = pos->next)
  81
  82 /**
  83  * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
  84  * @tpos:       the type * to use as a loop cursor.
  85  * @pos:        the &struct hlist_node to use as a loop cursor.
  86  * @member:     the name of the hlist_node within the struct.
  87  *
  88  */
  89 #define hlist_nulls_for_each_entry_from(tpos, pos, member)      \
  90         for (; (!is_a_nulls(pos)) &&                            \
  91                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
  92              pos = pos->next)
  93
  94 #endif