1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef __LINUX_GUARDS_H 3 #define __LINUX_GUARDS_H 4 5 #include <linux/compiler.h> 6 7 /* 8 * DEFINE_FREE(name, type, free): 9 * simple helper macro that defines the required wrapper for a __free() 10 * based cleanup function. @free is an expression using '_T' to access the 11 * variable. @free should typically include a NULL test before calling a 12 * function, see the example below. 13 * 14 * __free(name): 15 * variable attribute to add a scoped based cleanup to the variable. 16 * 17 * no_free_ptr(var): 18 * like a non-atomic xchg(var, NULL), such that the cleanup function will 19 * be inhibited -- provided it sanely deals with a NULL value. 20 * 21 * NOTE: this has __must_check semantics so that it is harder to accidentally 22 * leak the resource. 23 * 24 * return_ptr(p): 25 * returns p while inhibiting the __free(). 26 * 27 * Ex. 28 * 29 * DEFINE_FREE(kfree, void *, if (_T) kfree(_T)) 30 * 31 * void *alloc_obj(...) 32 * { 33 * struct obj *p __free(kfree) = kmalloc(...); 34 * if (!p) 35 * return NULL; 36 * 37 * if (!init_obj(p)) 38 * return NULL; 39 * 40 * return_ptr(p); 41 * } 42 * 43 * NOTE: the DEFINE_FREE()'s @free expression includes a NULL test even though 44 * kfree() is fine to be called with a NULL value. This is on purpose. This way 45 * the compiler sees the end of our alloc_obj() function as: 46 * 47 * tmp = p; 48 * p = NULL; 49 * if (p) 50 * kfree(p); 51 * return tmp; 52 * 53 * And through the magic of value-propagation and dead-code-elimination, it 54 * eliminates the actual cleanup call and compiles into: 55 * 56 * return p; 57 * 58 * Without the NULL test it turns into a mess and the compiler can't help us. 59 */ 60 61 #define DEFINE_FREE(_name, _type, _free) \ 62 static inline void __free_##_name(void *p) { _type _T = *(_type *)p; _free; } 63 64 #define __free(_name) __cleanup(__free_##_name) 65 66 #define __get_and_null_ptr(p) \ 67 ({ __auto_type __ptr = &(p); \ 68 __auto_type __val = *__ptr; \ 69 *__ptr = NULL; __val; }) 70 71 static inline __must_check 72 const volatile void * __must_check_fn(const volatile void *val) 73 { return val; } 74 75 #define no_free_ptr(p) \ 76 ((typeof(p)) __must_check_fn(__get_and_null_ptr(p))) 77 78 #define return_ptr(p) return no_free_ptr(p) 79 80 81 /* 82 * DEFINE_CLASS(name, type, exit, init, init_args...): 83 * helper to define the destructor and constructor for a type. 84 * @exit is an expression using '_T' -- similar to FREE above. 85 * @init is an expression in @init_args resulting in @type 86 * 87 * EXTEND_CLASS(name, ext, init, init_args...): 88 * extends class @name to @name@ext with the new constructor 89 * 90 * CLASS(name, var)(args...): 91 * declare the variable @var as an instance of the named class 92 * 93 * Ex. 94 * 95 * DEFINE_CLASS(fdget, struct fd, fdput(_T), fdget(fd), int fd) 96 * 97 * CLASS(fdget, f)(fd); 98 * if (!f.file) 99 * return -EBADF; 100 * 101 * // use 'f' without concern 102 */ 103 104 #define DEFINE_CLASS(_name, _type, _exit, _init, _init_args...) \ 105 typedef _type class_##_name##_t; \ 106 static inline void class_##_name##_destructor(_type *p) \ 107 { _type _T = *p; _exit; } \ 108 static inline _type class_##_name##_constructor(_init_args) \ 109 { _type t = _init; return t; } 110 111 #define EXTEND_CLASS(_name, ext, _init, _init_args...) \ 112 typedef class_##_name##_t class_##_name##ext##_t; \ 113 static inline void class_##_name##ext##_destructor(class_##_name##_t *p)\ 114 { class_##_name##_destructor(p); } \ 115 static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \ 116 { class_##_name##_t t = _init; return t; } 117 118 #define CLASS(_name, var) \ 119 class_##_name##_t var __cleanup(class_##_name##_destructor) = \ 120 class_##_name##_constructor 121 122 123 /* 124 * DEFINE_GUARD(name, type, lock, unlock): 125 * trivial wrapper around DEFINE_CLASS() above specifically 126 * for locks. 127 * 128 * guard(name): 129 * an anonymous instance of the (guard) class 130 * 131 * scoped_guard (name, args...) { }: 132 * similar to CLASS(name, scope)(args), except the variable (with the 133 * explicit name 'scope') is declard in a for-loop such that its scope is 134 * bound to the next (compound) statement. 135 * 136 */ 137 138 #define DEFINE_GUARD(_name, _type, _lock, _unlock) \ 139 DEFINE_CLASS(_name, _type, _unlock, ({ _lock; _T; }), _type _T) 140 141 #define guard(_name) \ 142 CLASS(_name, __UNIQUE_ID(guard)) 143 144 #define scoped_guard(_name, args...) \ 145 for (CLASS(_name, scope)(args), \ 146 *done = NULL; !done; done = (void *)1) 147 148 /* 149 * Additional helper macros for generating lock guards with types, either for 150 * locks that don't have a native type (eg. RCU, preempt) or those that need a 151 * 'fat' pointer (eg. spin_lock_irqsave). 152 * 153 * DEFINE_LOCK_GUARD_0(name, lock, unlock, ...) 154 * DEFINE_LOCK_GUARD_1(name, type, lock, unlock, ...) 155 * 156 * will result in the following type: 157 * 158 * typedef struct { 159 * type *lock; // 'type := void' for the _0 variant 160 * __VA_ARGS__; 161 * } class_##name##_t; 162 * 163 * As above, both _lock and _unlock are statements, except this time '_T' will 164 * be a pointer to the above struct. 165 */ 166 167 #define __DEFINE_UNLOCK_GUARD(_name, _type, _unlock, ...) \ 168 typedef struct { \ 169 _type *lock; \ 170 __VA_ARGS__; \ 171 } class_##_name##_t; \ 172 \ 173 static inline void class_##_name##_destructor(class_##_name##_t *_T) \ 174 { \ 175 if (_T->lock) { _unlock; } \ 176 } 177 178 179 #define __DEFINE_LOCK_GUARD_1(_name, _type, _lock) \ 180 static inline class_##_name##_t class_##_name##_constructor(_type *l) \ 181 { \ 182 class_##_name##_t _t = { .lock = l }, *_T = &_t; \ 183 _lock; \ 184 return _t; \ 185 } 186 187 #define __DEFINE_LOCK_GUARD_0(_name, _lock) \ 188 static inline class_##_name##_t class_##_name##_constructor(void) \ 189 { \ 190 class_##_name##_t _t = { .lock = (void*)1 }, \ 191 *_T __maybe_unused = &_t; \ 192 _lock; \ 193 return _t; \ 194 } 195 196 #define DEFINE_LOCK_GUARD_1(_name, _type, _lock, _unlock, ...) \ 197 __DEFINE_UNLOCK_GUARD(_name, _type, _unlock, __VA_ARGS__) \ 198 __DEFINE_LOCK_GUARD_1(_name, _type, _lock) 199 200 #define DEFINE_LOCK_GUARD_0(_name, _lock, _unlock, ...) \ 201 __DEFINE_UNLOCK_GUARD(_name, void, _unlock, __VA_ARGS__) \ 202 __DEFINE_LOCK_GUARD_0(_name, _lock) 203 204 #endif /* __LINUX_GUARDS_H */ 205