LXR linux/include/linux/list

   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
  21struct hlist_nulls_head {
  22        struct hlist_nulls_node *first;
  23};
  24
  25struct 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 */
  43static 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 */
  54static 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 */
  67static 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 */
  81static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
  82{
  83        return !READ_ONCE(h->pprev);
  84}
  85
  86static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
  87{
  88        return is_a_nulls(READ_ONCE(h->first));
  89}
  90
  91static 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
 103static 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
 113static 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
 146