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products/sources/formale Sprachen/C/Linux/include/linux/ (Open Source Betriebssystem Version 6.17.9^©) Datei vom 24.10.2025 mit Größe 4 kB

Quelle list_nulls.h Sprache: C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_LIST_NULLS_H
#define _LINUX_LIST_NULLS_H

#include <linux/poison.h>
#include <linux/const.h>

/*
* Special version of lists, where end of list is not a NULL pointer,
* but a 'nulls' marker, which can have many different values.
* (up to 2^31 different values guaranteed on all platforms)
*
* In the standard hlist, termination of a list is the NULL pointer.
* In this special 'nulls' variant, we use the fact that objects stored in
* a list are aligned on a word (4 or 8 bytes alignment).
* We therefore use the last significant bit of 'ptr' :
* Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
* Set to 0 : This is a pointer to some object (ptr)
*/

struct hlist_nulls_head {
struct hlist_nulls_node *first;
};

struct hlist_nulls_node {
struct hlist_nulls_node *next, **pprev;
};
#define NULLS_MARKER(value) (1UL | (((long)value) << 1))
#define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
#define HLIST_NULLS_HEAD_INIT(nulls) {.first = (struct hlist_nulls_node *)NULLS_MARKER(nulls)}

#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)

#define hlist_nulls_entry_safe(ptr, type, member) \
({ typeof(ptr) ____ptr = (ptr); \
    !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
})
/**
* ptr_is_a_nulls - Test if a ptr is a nulls
* @ptr: ptr to be tested
*
*/
static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
{
return ((unsigned long)ptr & 1);
}

/**
* get_nulls_value - Get the 'nulls' value of the end of chain
* @ptr: end of chain
*
* Should be called only if is_a_nulls(ptr);
*/
static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
{
return ((unsigned long)ptr) >> 1;
}

/**
* hlist_nulls_unhashed - Has node been removed and reinitialized?
* @h: Node to be checked
*
* Not that not all removal functions will leave a node in unhashed state.
* For example, hlist_del_init_rcu() leaves the node in unhashed state,
* but hlist_nulls_del() does not.
*/
static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
{
return !h->pprev;
}

/**
* hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
* @h: Node to be checked
*
* Not that not all removal functions will leave a node in unhashed state.
* For example, hlist_del_init_rcu() leaves the node in unhashed state,
* but hlist_nulls_del() does not.  Unlike hlist_nulls_unhashed(), this
* function may be used locklessly.
*/
static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
{
return !READ_ONCE(h->pprev);
}

static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
{
return is_a_nulls(READ_ONCE(h->first));
}

static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
     struct hlist_nulls_head *h)
{
struct hlist_nulls_node *first = h->first;

n->next = first;
WRITE_ONCE(n->pprev, &h->first);
h->first = n;
if (!is_a_nulls(first))
  WRITE_ONCE(first->pprev, &n->next);
}

static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
{
struct hlist_nulls_node *next = n->next;
struct hlist_nulls_node **pprev = n->pprev;

WRITE_ONCE(*pprev, next);
if (!is_a_nulls(next))
  WRITE_ONCE(next->pprev, pprev);
}

static inline void hlist_nulls_del(struct hlist_nulls_node *n)
{
__hlist_nulls_del(n);
WRITE_ONCE(n->pprev, LIST_POISON2);
}

/**
* hlist_nulls_for_each_entry - iterate over list of given type
* @tpos: the type * to use as a loop cursor.
* @pos: the &struct hlist_node to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the hlist_node within the struct.
*
*/
#define hlist_nulls_for_each_entry(tpos, pos, head, member)         \
for (pos = (head)->first;            \
      (!is_a_nulls(pos)) &&            \
  ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
      pos = pos->next)

/**
* hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
* @tpos: the type * to use as a loop cursor.
* @pos: the &struct hlist_node to use as a loop cursor.
* @member: the name of the hlist_node within the struct.
*
*/
#define hlist_nulls_for_each_entry_from(tpos, pos, member) \
for (; (!is_a_nulls(pos)) &&     \
  ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
      pos = pos->next)

#endif

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