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
__must_check_fn(const volatile void * val)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 * DEFINE_GUARD_COND(name, ext, condlock)
129 * wrapper around EXTEND_CLASS above to add conditional lock
130 * variants to a base class, eg. mutex_trylock() or
131 * mutex_lock_interruptible().
132 *
133 * guard(name):
134 * an anonymous instance of the (guard) class, not recommended for
135 * conditional locks.
136 *
137 * scoped_guard (name, args...) { }:
138 * similar to CLASS(name, scope)(args), except the variable (with the
139 * explicit name 'scope') is declard in a for-loop such that its scope is
140 * bound to the next (compound) statement.
141 *
142 * for conditional locks the loop body is skipped when the lock is not
143 * acquired.
144 *
145 * scoped_cond_guard (name, fail, args...) { }:
146 * similar to scoped_guard(), except it does fail when the lock
147 * acquire fails.
148 *
149 */
150
151 #define DEFINE_GUARD(_name, _type, _lock, _unlock) \
152 DEFINE_CLASS(_name, _type, if (_T) { _unlock; }, ({ _lock; _T; }), _type _T); \
153 static inline void * class_##_name##_lock_ptr(class_##_name##_t *_T) \
154 { return *_T; }
155
156 #define DEFINE_GUARD_COND(_name, _ext, _condlock) \
157 EXTEND_CLASS(_name, _ext, \
158 ({ void *_t = _T; if (_T && !(_condlock)) _t = NULL; _t; }), \
159 class_##_name##_t _T) \
160 static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
161 { return class_##_name##_lock_ptr(_T); }
162
163 #define guard(_name) \
164 CLASS(_name, __UNIQUE_ID(guard))
165
166 #define __guard_ptr(_name) class_##_name##_lock_ptr
167
168 #define scoped_guard(_name, args...) \
169 for (CLASS(_name, scope)(args), \
170 *done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)
171
172 #define scoped_cond_guard(_name, _fail, args...) \
173 for (CLASS(_name, scope)(args), \
174 *done = NULL; !done; done = (void *)1) \
175 if (!__guard_ptr(_name)(&scope)) _fail; \
176 else
177
178 /*
179 * Additional helper macros for generating lock guards with types, either for
180 * locks that don't have a native type (eg. RCU, preempt) or those that need a
181 * 'fat' pointer (eg. spin_lock_irqsave).
182 *
183 * DEFINE_LOCK_GUARD_0(name, lock, unlock, ...)
184 * DEFINE_LOCK_GUARD_1(name, type, lock, unlock, ...)
185 * DEFINE_LOCK_GUARD_1_COND(name, ext, condlock)
186 *
187 * will result in the following type:
188 *
189 * typedef struct {
190 * type *lock; // 'type := void' for the _0 variant
191 * __VA_ARGS__;
192 * } class_##name##_t;
193 *
194 * As above, both _lock and _unlock are statements, except this time '_T' will
195 * be a pointer to the above struct.
196 */
197
198 #define __DEFINE_UNLOCK_GUARD(_name, _type, _unlock, ...) \
199 typedef struct { \
200 _type *lock; \
201 __VA_ARGS__; \
202 } class_##_name##_t; \
203 \
204 static inline void class_##_name##_destructor(class_##_name##_t *_T) \
205 { \
206 if (_T->lock) { _unlock; } \
207 } \
208 \
209 static inline void *class_##_name##_lock_ptr(class_##_name##_t *_T) \
210 { \
211 return _T->lock; \
212 }
213
214
215 #define __DEFINE_LOCK_GUARD_1(_name, _type, _lock) \
216 static inline class_##_name##_t class_##_name##_constructor(_type *l) \
217 { \
218 class_##_name##_t _t = { .lock = l }, *_T = &_t; \
219 _lock; \
220 return _t; \
221 }
222
223 #define __DEFINE_LOCK_GUARD_0(_name, _lock) \
224 static inline class_##_name##_t class_##_name##_constructor(void) \
225 { \
226 class_##_name##_t _t = { .lock = (void*)1 }, \
227 *_T __maybe_unused = &_t; \
228 _lock; \
229 return _t; \
230 }
231
232 #define DEFINE_LOCK_GUARD_1(_name, _type, _lock, _unlock, ...) \
233 __DEFINE_UNLOCK_GUARD(_name, _type, _unlock, __VA_ARGS__) \
234 __DEFINE_LOCK_GUARD_1(_name, _type, _lock)
235
236 #define DEFINE_LOCK_GUARD_0(_name, _lock, _unlock, ...) \
237 __DEFINE_UNLOCK_GUARD(_name, void, _unlock, __VA_ARGS__) \
238 __DEFINE_LOCK_GUARD_0(_name, _lock)
239
240 #define DEFINE_LOCK_GUARD_1_COND(_name, _ext, _condlock) \
241 EXTEND_CLASS(_name, _ext, \
242 ({ class_##_name##_t _t = { .lock = l }, *_T = &_t;\
243 if (_T->lock && !(_condlock)) _T->lock = NULL; \
244 _t; }), \
245 typeof_member(class_##_name##_t, lock) l) \
246 static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
247 { return class_##_name##_lock_ptr(_T); }
248
249
250 #endif /* __LINUX_GUARDS_H */
251