include/linux/list_nulls.h

   1 #ifndef _LINUX_LIST_NULLS_H
   2 #define _LINUX_LIST_NULLS_H
   3
   4 #include <linux/poison.h>
   5 #include <linux/const.h>
   6
   7 /*
   8  * Special version of lists, where end of list is not a NULL pointer,
   9  * but a 'nulls' marker, which can have many different values.
  10  * (up to 2^31 different values guaranteed on all platforms)
  11  *
  12  * In the standard hlist, termination of a list is the NULL pointer.
  13  * In this special 'nulls' variant, we use the fact that objects stored in
  14  * a list are aligned on a word (4 or 8 bytes alignment).
  15  * We therefore use the last significant bit of 'ptr' :
  16  * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
  17  * Set to 0 : This is a pointer to some object (ptr)
  18  */
  19
  20 struct hlist_nulls_head {
  21         struct hlist_nulls_node *first;
  22 };
  23
  24 struct hlist_nulls_node {
  25         struct hlist_nulls_node *next, **pprev;
  26 };
  27 #define NULLS_MARKER(value) (1UL | (((long)value) << 1))
  28 #define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
  29         ((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
  30
  31 #define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
  32
  33 #define hlist_nulls_entry_safe(ptr, type, member) \
  34         ({ typeof(ptr) ____ptr = (ptr); \
  35            !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
  36         })
  37 /**
  38  * ptr_is_a_nulls - Test if a ptr is a nulls
  39  * @ptr: ptr to be tested
  40  *
  41  */
  42 static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
  43 {
  44         return ((unsigned long)ptr & 1);
  45 }
  46
  47 /**
  48  * get_nulls_value - Get the 'nulls' value of the end of chain
  49  * @ptr: end of chain
  50  *
  51  * Should be called only if is_a_nulls(ptr);
  52  */
  53 static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
  54 {
  55         return ((unsigned long)ptr) >> 1;
  56 }
  57
  58 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
  59 {
  60         return !h->pprev;
  61 }
  62
  63 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
  64 {
  65         return is_a_nulls(READ_ONCE(h->first));
  66 }
  67
  68 static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
  69                                         struct hlist_nulls_head *h)
  70 {
  71         struct hlist_nulls_node *first = h->first;
  72
  73         n->next = first;
  74         n->pprev = &h->first;
  75         h->first = n;
  76         if (!is_a_nulls(first))
  77                 first->pprev = &n->next;
  78 }
  79
  80 static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
  81 {
  82         struct hlist_nulls_node *next = n->next;
  83         struct hlist_nulls_node **pprev = n->pprev;
  84
  85         WRITE_ONCE(*pprev, next);
  86         if (!is_a_nulls(next))
  87                 next->pprev = pprev;
  88 }
  89
  90 static inline void hlist_nulls_del(struct hlist_nulls_node *n)
  91 {
  92         __hlist_nulls_del(n);
  93         n->pprev = LIST_POISON2;
  94 }
  95
  96 /**
  97  * hlist_nulls_for_each_entry   - iterate over list of given type
  98  * @tpos:       the type * to use as a loop cursor.
  99  * @pos:        the &struct hlist_node to use as a loop cursor.
 100  * @head:       the head for your list.
 101  * @member:     the name of the hlist_node within the struct.
 102  *
 103  */
 104 #define hlist_nulls_for_each_entry(tpos, pos, head, member)                    \
 105         for (pos = (head)->first;                                              \
 106              (!is_a_nulls(pos)) &&                                             \
 107                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
 108              pos = pos->next)
 109
 110 /**
 111  * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
 112  * @tpos:       the type * to use as a loop cursor.
 113  * @pos:        the &struct hlist_node to use as a loop cursor.
 114  * @member:     the name of the hlist_node within the struct.
 115  *
 116  */
 117 #define hlist_nulls_for_each_entry_from(tpos, pos, member)      \
 118         for (; (!is_a_nulls(pos)) &&                            \
 119                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
 120              pos = pos->next)
 121
 122 #endif