list_nulls.h

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/* 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; \
    })
static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
{
    return ((unsigned long)ptr & 1);
}
 
static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
{
    return ((unsigned long)ptr) >> 1;
}
 
static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
{
    return !h->pprev;
}
 
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);
}
 
#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)
 
#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