1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _LINUX_LIST_NULLS_H 3 #define _LINUX_LIST_NULLS_H 4 5 #include <linux/poison.h> 6 #include <linux/const.h> 7 8 /* 9 * Special version of lists, where end of list is not a NULL pointer, 10 * but a 'nulls' marker, which can have many different values. 11 * (up to 2^31 different values guaranteed on all platforms) 12 * 13 * In the standard hlist, termination of a list is the NULL pointer. 14 * In this special 'nulls' variant, we use the fact that objects stored in 15 * a list are aligned on a word (4 or 8 bytes alignment). 16 * We therefore use the last significant bit of 'ptr' : 17 * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1) 18 * Set to 0 : This is a pointer to some object (ptr) 19 */ 20 21 struct hlist_nulls_head { 22 struct hlist_nulls_node *first; 23 }; 24 25 struct hlist_nulls_node { 26 struct hlist_nulls_node *next, **pprev; 27 }; 28 #define NULLS_MARKER(value) (1UL | (((long)value) << 1)) 29 #define INIT_HLIST_NULLS_HEAD(ptr, nulls) \ 30 ((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls)) 31 32 #define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member) 33 34 #define hlist_nulls_entry_safe(ptr, type, member) \ 35 ({ typeof(ptr) ____ptr = (ptr); \ 36 !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \ 37 }) 38 /** 39 * ptr_is_a_nulls - Test if a ptr is a nulls 40 * @ptr: ptr to be tested 41 * 42 */ 43 static inline int is_a_nulls(const struct hlist_nulls_node *ptr) 44 { 45 return ((unsigned long)ptr & 1); 46 } 47 48 /** 49 * get_nulls_value - Get the 'nulls' value of the end of chain 50 * @ptr: end of chain 51 * 52 * Should be called only if is_a_nulls(ptr); 53 */ 54 static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr) 55 { 56 return ((unsigned long)ptr) >> 1; 57 } 58 59 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h) 60 { 61 return !h->pprev; 62 } 63 64 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h) 65 { 66 return is_a_nulls(READ_ONCE(h->first)); 67 } 68 69 static inline void hlist_nulls_add_head(struct hlist_nulls_node *n, 70 struct hlist_nulls_head *h) 71 { 72 struct hlist_nulls_node *first = h->first; 73 74 n->next = first; 75 n->pprev = &h->first; 76 h->first = n; 77 if (!is_a_nulls(first)) 78 first->pprev = &n->next; 79 } 80 81 static inline void __hlist_nulls_del(struct hlist_nulls_node *n) 82 { 83 struct hlist_nulls_node *next = n->next; 84 struct hlist_nulls_node **pprev = n->pprev; 85 86 WRITE_ONCE(*pprev, next); 87 if (!is_a_nulls(next)) 88 next->pprev = pprev; 89 } 90 91 static inline void hlist_nulls_del(struct hlist_nulls_node *n) 92 { 93 __hlist_nulls_del(n); 94 n->pprev = LIST_POISON2; 95 } 96 97 /** 98 * hlist_nulls_for_each_entry - iterate over list of given type 99 * @tpos: the type * to use as a loop cursor. 100 * @pos: the &struct hlist_node to use as a loop cursor. 101 * @head: the head for your list. 102 * @member: the name of the hlist_node within the struct. 103 * 104 */ 105 #define hlist_nulls_for_each_entry(tpos, pos, head, member) \ 106 for (pos = (head)->first; \ 107 (!is_a_nulls(pos)) && \ 108 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \ 109 pos = pos->next) 110 111 /** 112 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point 113 * @tpos: the type * to use as a loop cursor. 114 * @pos: the &struct hlist_node to use as a loop cursor. 115 * @member: the name of the hlist_node within the struct. 116 * 117 */ 118 #define hlist_nulls_for_each_entry_from(tpos, pos, member) \ 119 for (; (!is_a_nulls(pos)) && \ 120 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \ 121 pos = pos->next) 122 123 #endif 124