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