include/linux/list_nulls.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _LINUX_LIST_NULLS_H
   3 #define _LINUX_LIST_NULLS_H
   4
   5 #include <linux/poison.h>
   6 #include <linux/const.h>
   7
   8 /*
   9  * Special version of lists, where end of list is not a NULL pointer,
  10  * but a 'nulls' marker, which can have many different values.
  11  * (up to 2^31 different values guaranteed on all platforms)
  12  *
  13  * In the standard hlist, termination of a list is the NULL pointer.
  14  * In this special 'nulls' variant, we use the fact that objects stored in
  15  * a list are aligned on a word (4 or 8 bytes alignment).
  16  * We therefore use the last significant bit of 'ptr' :
  17  * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
  18  * Set to 0 : This is a pointer to some object (ptr)
  19  */
  20
  21 struct hlist_nulls_head {
  22         struct hlist_nulls_node *first;
  23 };
  24
  25 struct hlist_nulls_node {
  26         struct hlist_nulls_node *next, **pprev;
  27 };
  28 #define NULLS_MARKER(value) (1UL | (((long)value) << 1))
  29 #define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
  30         ((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
  31
  32 #define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
  33
  34 #define hlist_nulls_entry_safe(ptr, type, member) \
  35         ({ typeof(ptr) ____ptr = (ptr); \
  36            !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
  37         })
  38 /**
  39  * ptr_is_a_nulls - Test if a ptr is a nulls
  40  * @ptr: ptr to be tested
  41  *
  42  */
  43 static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
  44 {
  45         return ((unsigned long)ptr & 1);
  46 }
  47
  48 /**
  49  * get_nulls_value - Get the 'nulls' value of the end of chain
  50  * @ptr: end of chain
  51  *
  52  * Should be called only if is_a_nulls(ptr);
  53  */
  54 static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
  55 {
  56         return ((unsigned long)ptr) >> 1;
  57 }
  58
  59 /**
  60  * hlist_nulls_unhashed - Has node been removed and reinitialized?
  61  * @h: Node to be checked
  62  *
  63  * Not that not all removal functions will leave a node in unhashed state.
  64  * For example, hlist_del_init_rcu() leaves the node in unhashed state,
  65  * but hlist_nulls_del() does not.
  66  */
  67 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
  68 {
  69         return !h->pprev;
  70 }
  71
  72 /**
  73  * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
  74  * @h: Node to be checked
  75  *
  76  * Not that not all removal functions will leave a node in unhashed state.
  77  * For example, hlist_del_init_rcu() leaves the node in unhashed state,
  78  * but hlist_nulls_del() does not.  Unlike hlist_nulls_unhashed(), this
  79  * function may be used locklessly.
  80  */
  81 static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
  82 {
  83         return !READ_ONCE(h->pprev);
  84 }
  85
  86 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
  87 {
  88         return is_a_nulls(READ_ONCE(h->first));
  89 }
  90
  91 static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
  92                                         struct hlist_nulls_head *h)
  93 {
  94         struct hlist_nulls_node *first = h->first;
  95
  96         n->next = first;
  97         WRITE_ONCE(n->pprev, &h->first);
  98         h->first = n;
  99         if (!is_a_nulls(first))
 100                 WRITE_ONCE(first->pprev, &n->next);
 101 }
 102
 103 static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
 104 {
 105         struct hlist_nulls_node *next = n->next;
 106         struct hlist_nulls_node **pprev = n->pprev;
 107
 108         WRITE_ONCE(*pprev, next);
 109         if (!is_a_nulls(next))
 110                 WRITE_ONCE(next->pprev, pprev);
 111 }
 112
 113 static inline void hlist_nulls_del(struct hlist_nulls_node *n)
 114 {
 115         __hlist_nulls_del(n);
 116         WRITE_ONCE(n->pprev, LIST_POISON2);
 117 }
 118
 119 /**
 120  * hlist_nulls_for_each_entry   - iterate over list of given type
 121  * @tpos:       the type * to use as a loop cursor.
 122  * @pos:        the &struct hlist_node to use as a loop cursor.
 123  * @head:       the head for your list.
 124  * @member:     the name of the hlist_node within the struct.
 125  *
 126  */
 127 #define hlist_nulls_for_each_entry(tpos, pos, head, member)                    \
 128         for (pos = (head)->first;                                              \
 129              (!is_a_nulls(pos)) &&                                             \
 130                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
 131              pos = pos->next)
 132
 133 /**
 134  * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
 135  * @tpos:       the type * to use as a loop cursor.
 136  * @pos:        the &struct hlist_node to use as a loop cursor.
 137  * @member:     the name of the hlist_node within the struct.
 138  *
 139  */
 140 #define hlist_nulls_for_each_entry_from(tpos, pos, member)      \
 141         for (; (!is_a_nulls(pos)) &&                            \
 142                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
 143              pos = pos->next)
 144
 145 #endif