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
  59static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
  60{
  61        return !h->pprev;
  62}
  63
  64static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
  65{
  66        return is_a_nulls(READ_ONCE(h->first));
  67}
  68
  69static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
  70                                        struct hlist_nulls_head *h)
  71{
  72        struct hlist_nulls_node *first = h->first;
  73
  74        n->next = first;
  75        n->pprev = &h->first;
  76        h->first = n;
  77        if (!is_a_nulls(first))
  78                first->pprev = &n->next;
  79}
  80
  81static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
  82{
  83        struct hlist_nulls_node *next = n->next;
  84        struct hlist_nulls_node **pprev = n->pprev;
  85
  86        WRITE_ONCE(*pprev, next);
  87        if (!is_a_nulls(next))
  88                next->pprev = pprev;
  89}
  90
  91static inline void hlist_nulls_del(struct hlist_nulls_node *n)
  92{
  93        __hlist_nulls_del(n);
  94        n->pprev = LIST_POISON2;
  95}
  96
  97/**
  98 * hlist_nulls_for_each_entry   - iterate over list of given type
  99 * @tpos:       the type * to use as a loop cursor.
 100 * @pos:        the &struct hlist_node to use as a loop cursor.
 101 * @head:       the head for your list.
 102 * @member:     the name of the hlist_node within the struct.
 103 *
 104 */
 105#define hlist_nulls_for_each_entry(tpos, pos, head, member)                    \
 106        for (pos = (head)->first;                                              \
 107             (!is_a_nulls(pos)) &&                                             \
 108                ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
 109             pos = pos->next)
 110
 111/**
 112 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
 113 * @tpos:       the type * to use as a loop cursor.
 114 * @pos:        the &struct hlist_node to use as a loop cursor.
 115 * @member:     the name of the hlist_node within the struct.
 116 *
 117 */
 118#define hlist_nulls_for_each_entry_from(tpos, pos, member)      \
 119        for (; (!is_a_nulls(pos)) &&                            \
 120                ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
 121             pos = pos->next)
 122
 123#endif
 124