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_del(struct hlist_nulls_node *n) 60 { 61 struct hlist_nulls_node *next = n->next; 62 struct hlist_nulls_node **pprev = n->pprev; 63 *pprev = next; 64 if (!is_a_nulls(next)) 65 next->pprev = pprev; 66 } 67 68 /** 69 * hlist_nulls_for_each_entry - iterate over list of given type 70 * @tpos: the type * to use as a loop cursor. 71 * @pos: the &struct hlist_node to use as a loop cursor. 72 * @head: the head for your list. 73 * @member: the name of the hlist_node within the struct. 74 * 75 */ 76 #define hlist_nulls_for_each_entry(tpos, pos, head, member) \ 77 for (pos = (head)->first; \ 78 (!is_a_nulls(pos)) && \ 79 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \ 80 pos = pos->next) 81 82 /** 83 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point 84 * @tpos: the type * to use as a loop cursor. 85 * @pos: the &struct hlist_node to use as a loop cursor. 86 * @member: the name of the hlist_node within the struct. 87 * 88 */ 89 #define hlist_nulls_for_each_entry_from(tpos, pos, member) \ 90 for (; (!is_a_nulls(pos)) && \ 91 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \ 92 pos = pos->next) 93 94 #endif 95