Release 4.12 include/linux/list_nulls.h

#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_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);
}

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/**
 * 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;
}

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static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
{
	return !h->pprev;
}

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

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

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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))
		next->pprev = pprev;
}

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

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/**
 * 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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Directory: include/linux

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