include/linux/list_nulls.h

   1 #ifndef _LINUX_LIST_NULLS_H
   2 #define _LINUX_LIST_NULLS_H
   3
   4 #include <linux/poison.h>
   5 #include <linux/const.h>
   6
   7 /*
   8  * Special version of lists, where end of list is not a NULL pointer,
   9  * but a 'nulls' marker, which can have many different values.
  10  * (up to 2^31 different values guaranteed on all platforms)
  11  *
  12  * In the standard hlist, termination of a list is the NULL pointer.
  13  * In this special 'nulls' variant, we use the fact that objects stored in
  14  * a list are aligned on a word (4 or 8 bytes alignment).
  15  * We therefore use the last significant bit of 'ptr' :
  16  * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
  17  * Set to 0 : This is a pointer to some object (ptr)
  18  */
  19
  20 struct hlist_nulls_head {
  21         struct hlist_nulls_node *first;
  22 };
  23
  24 struct hlist_nulls_node {
  25         struct hlist_nulls_node *next, **pprev;
  26 };
  27 #define NULLS_MARKER(value) (1UL | (((long)value) << 1))
  28 #define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
  29         ((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
  30
  31 #define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
  32 /**
  33  * ptr_is_a_nulls - Test if a ptr is a nulls
  34  * @ptr: ptr to be tested
  35  *
  36  */
  37 static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
  38 {
  39         return ((unsigned long)ptr & 1);
  40 }
  41
  42 /**
  43  * get_nulls_value - Get the 'nulls' value of the end of chain
  44  * @ptr: end of chain
  45  *
  46  * Should be called only if is_a_nulls(ptr);
  47  */
  48 static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
  49 {
  50         return ((unsigned long)ptr) >> 1;
  51 }
  52
  53 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
  54 {
  55         return !h->pprev;
  56 }
  57
  58 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
  59 {
  60         return is_a_nulls(READ_ONCE(h->first));
  61 }
  62
  63 static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
  64                                         struct hlist_nulls_head *h)
  65 {
  66         struct hlist_nulls_node *first = h->first;
  67
  68         n->next = first;
  69         n->pprev = &h->first;
  70         h->first = n;
  71         if (!is_a_nulls(first))
  72                 first->pprev = &n->next;
  73 }
  74
  75 static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
  76 {
  77         struct hlist_nulls_node *next = n->next;
  78         struct hlist_nulls_node **pprev = n->pprev;
  79
  80         WRITE_ONCE(*pprev, next);
  81         if (!is_a_nulls(next))
  82                 next->pprev = pprev;
  83 }
  84
  85 static inline void hlist_nulls_del(struct hlist_nulls_node *n)
  86 {
  87         __hlist_nulls_del(n);
  88         n->pprev = LIST_POISON2;
  89 }
  90
  91 /**
  92  * hlist_nulls_for_each_entry   - iterate over list of given type
  93  * @tpos:       the type * to use as a loop cursor.
  94  * @pos:        the &struct hlist_node to use as a loop cursor.
  95  * @head:       the head for your list.
  96  * @member:     the name of the hlist_node within the struct.
  97  *
  98  */
  99 #define hlist_nulls_for_each_entry(tpos, pos, head, member)                    \
 100         for (pos = (head)->first;                                              \
 101              (!is_a_nulls(pos)) &&                                             \
 102                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
 103              pos = pos->next)
 104
 105 /**
 106  * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
 107  * @tpos:       the type * to use as a loop cursor.
 108  * @pos:        the &struct hlist_node to use as a loop cursor.
 109  * @member:     the name of the hlist_node within the struct.
 110  *
 111  */
 112 #define hlist_nulls_for_each_entry_from(tpos, pos, member)      \
 113         for (; (!is_a_nulls(pos)) &&                            \
 114                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
 115              pos = pos->next)
 116
 117 #endif