251 lines
7.5 KiB
C
251 lines
7.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __LINUX_GUARDS_H
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#define __LINUX_GUARDS_H
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#include <linux/compiler.h>
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/*
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* DEFINE_FREE(name, type, free):
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* simple helper macro that defines the required wrapper for a __free()
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* based cleanup function. @free is an expression using '_T' to access the
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* variable. @free should typically include a NULL test before calling a
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* function, see the example below.
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*
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* __free(name):
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* variable attribute to add a scoped based cleanup to the variable.
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*
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* no_free_ptr(var):
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* like a non-atomic xchg(var, NULL), such that the cleanup function will
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* be inhibited -- provided it sanely deals with a NULL value.
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*
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* NOTE: this has __must_check semantics so that it is harder to accidentally
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* leak the resource.
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*
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* return_ptr(p):
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* returns p while inhibiting the __free().
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*
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* Ex.
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*
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* DEFINE_FREE(kfree, void *, if (_T) kfree(_T))
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*
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* void *alloc_obj(...)
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* {
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* struct obj *p __free(kfree) = kmalloc(...);
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* if (!p)
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* return NULL;
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*
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* if (!init_obj(p))
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* return NULL;
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*
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* return_ptr(p);
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* }
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*
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* NOTE: the DEFINE_FREE()'s @free expression includes a NULL test even though
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* kfree() is fine to be called with a NULL value. This is on purpose. This way
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* the compiler sees the end of our alloc_obj() function as:
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*
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* tmp = p;
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* p = NULL;
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* if (p)
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* kfree(p);
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* return tmp;
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*
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* And through the magic of value-propagation and dead-code-elimination, it
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* eliminates the actual cleanup call and compiles into:
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*
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* return p;
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*
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* Without the NULL test it turns into a mess and the compiler can't help us.
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*/
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#define DEFINE_FREE(_name, _type, _free) \
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static inline void __free_##_name(void *p) { _type _T = *(_type *)p; _free; }
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#define __free(_name) __cleanup(__free_##_name)
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#define __get_and_null_ptr(p) \
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({ __auto_type __ptr = &(p); \
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__auto_type __val = *__ptr; \
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*__ptr = NULL; __val; })
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static inline __must_check
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const volatile void * __must_check_fn(const volatile void *val)
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{ return val; }
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#define no_free_ptr(p) \
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((typeof(p)) __must_check_fn(__get_and_null_ptr(p)))
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#define return_ptr(p) return no_free_ptr(p)
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/*
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* DEFINE_CLASS(name, type, exit, init, init_args...):
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* helper to define the destructor and constructor for a type.
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* @exit is an expression using '_T' -- similar to FREE above.
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* @init is an expression in @init_args resulting in @type
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*
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* EXTEND_CLASS(name, ext, init, init_args...):
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* extends class @name to @name@ext with the new constructor
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*
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* CLASS(name, var)(args...):
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* declare the variable @var as an instance of the named class
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*
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* Ex.
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*
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* DEFINE_CLASS(fdget, struct fd, fdput(_T), fdget(fd), int fd)
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*
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* CLASS(fdget, f)(fd);
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* if (!f.file)
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* return -EBADF;
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*
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* // use 'f' without concern
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*/
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#define DEFINE_CLASS(_name, _type, _exit, _init, _init_args...) \
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typedef _type class_##_name##_t; \
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static inline void class_##_name##_destructor(_type *p) \
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{ _type _T = *p; _exit; } \
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static inline _type class_##_name##_constructor(_init_args) \
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{ _type t = _init; return t; }
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#define EXTEND_CLASS(_name, ext, _init, _init_args...) \
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typedef class_##_name##_t class_##_name##ext##_t; \
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static inline void class_##_name##ext##_destructor(class_##_name##_t *p)\
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{ class_##_name##_destructor(p); } \
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static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
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{ class_##_name##_t t = _init; return t; }
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#define CLASS(_name, var) \
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class_##_name##_t var __cleanup(class_##_name##_destructor) = \
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class_##_name##_constructor
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/*
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* DEFINE_GUARD(name, type, lock, unlock):
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* trivial wrapper around DEFINE_CLASS() above specifically
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* for locks.
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*
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* DEFINE_GUARD_COND(name, ext, condlock)
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* wrapper around EXTEND_CLASS above to add conditional lock
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* variants to a base class, eg. mutex_trylock() or
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* mutex_lock_interruptible().
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*
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* guard(name):
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* an anonymous instance of the (guard) class, not recommended for
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* conditional locks.
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*
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* scoped_guard (name, args...) { }:
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* similar to CLASS(name, scope)(args), except the variable (with the
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* explicit name 'scope') is declard in a for-loop such that its scope is
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* bound to the next (compound) statement.
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*
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* for conditional locks the loop body is skipped when the lock is not
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* acquired.
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*
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* scoped_cond_guard (name, fail, args...) { }:
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* similar to scoped_guard(), except it does fail when the lock
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* acquire fails.
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*
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*/
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#define DEFINE_GUARD(_name, _type, _lock, _unlock) \
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DEFINE_CLASS(_name, _type, if (_T) { _unlock; }, ({ _lock; _T; }), _type _T); \
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static inline void * class_##_name##_lock_ptr(class_##_name##_t *_T) \
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{ return *_T; }
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#define DEFINE_GUARD_COND(_name, _ext, _condlock) \
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EXTEND_CLASS(_name, _ext, \
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({ void *_t = _T; if (_T && !(_condlock)) _t = NULL; _t; }), \
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class_##_name##_t _T) \
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static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
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{ return class_##_name##_lock_ptr(_T); }
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#define guard(_name) \
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CLASS(_name, __UNIQUE_ID(guard))
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#define __guard_ptr(_name) class_##_name##_lock_ptr
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#define scoped_guard(_name, args...) \
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for (CLASS(_name, scope)(args), \
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*done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)
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#define scoped_cond_guard(_name, _fail, args...) \
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for (CLASS(_name, scope)(args), \
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*done = NULL; !done; done = (void *)1) \
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if (!__guard_ptr(_name)(&scope)) _fail; \
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else
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/*
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* Additional helper macros for generating lock guards with types, either for
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* locks that don't have a native type (eg. RCU, preempt) or those that need a
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* 'fat' pointer (eg. spin_lock_irqsave).
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*
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* DEFINE_LOCK_GUARD_0(name, lock, unlock, ...)
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* DEFINE_LOCK_GUARD_1(name, type, lock, unlock, ...)
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* DEFINE_LOCK_GUARD_1_COND(name, ext, condlock)
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*
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* will result in the following type:
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*
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* typedef struct {
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* type *lock; // 'type := void' for the _0 variant
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* __VA_ARGS__;
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* } class_##name##_t;
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*
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* As above, both _lock and _unlock are statements, except this time '_T' will
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* be a pointer to the above struct.
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*/
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#define __DEFINE_UNLOCK_GUARD(_name, _type, _unlock, ...) \
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typedef struct { \
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_type *lock; \
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__VA_ARGS__; \
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} class_##_name##_t; \
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\
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static inline void class_##_name##_destructor(class_##_name##_t *_T) \
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{ \
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if (_T->lock) { _unlock; } \
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} \
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\
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static inline void *class_##_name##_lock_ptr(class_##_name##_t *_T) \
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{ \
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return _T->lock; \
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}
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#define __DEFINE_LOCK_GUARD_1(_name, _type, _lock) \
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static inline class_##_name##_t class_##_name##_constructor(_type *l) \
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{ \
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class_##_name##_t _t = { .lock = l }, *_T = &_t; \
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_lock; \
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return _t; \
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}
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#define __DEFINE_LOCK_GUARD_0(_name, _lock) \
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static inline class_##_name##_t class_##_name##_constructor(void) \
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{ \
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class_##_name##_t _t = { .lock = (void*)1 }, \
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*_T __maybe_unused = &_t; \
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_lock; \
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return _t; \
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}
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#define DEFINE_LOCK_GUARD_1(_name, _type, _lock, _unlock, ...) \
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__DEFINE_UNLOCK_GUARD(_name, _type, _unlock, __VA_ARGS__) \
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__DEFINE_LOCK_GUARD_1(_name, _type, _lock)
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#define DEFINE_LOCK_GUARD_0(_name, _lock, _unlock, ...) \
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__DEFINE_UNLOCK_GUARD(_name, void, _unlock, __VA_ARGS__) \
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__DEFINE_LOCK_GUARD_0(_name, _lock)
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#define DEFINE_LOCK_GUARD_1_COND(_name, _ext, _condlock) \
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EXTEND_CLASS(_name, _ext, \
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({ class_##_name##_t _t = { .lock = l }, *_T = &_t;\
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if (_T->lock && !(_condlock)) _T->lock = NULL; \
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_t; }), \
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typeof_member(class_##_name##_t, lock) l) \
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static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
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{ return class_##_name##_lock_ptr(_T); }
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#endif /* __LINUX_GUARDS_H */
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