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 123