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include/linux/list_nulls.h
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#ifndef _LINUX_LIST_NULLS_H
#define _LINUX_LIST_NULLS_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 INIT_HLIST_NULLS_HEAD(ptr, nulls) \
((ptr)->first = (struct hlist_nulls_node *) (1UL | (((long)nulls) << 1)))
#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
/**
* 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;
}
static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
{
return !h->pprev;
}
static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
{
return is_a_nulls(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;
*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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