arch/x86/include/asm/atomic.h

#ifndef _ASM_X86_ATOMIC_H
#define _ASM_X86_ATOMIC_H

#include <linux/compiler.h>
#include <linux/types.h>
#include <asm/processor.h>

typedef struct { volatile int counter; } atomic_t;

/*
 * Atomic operations that C can't guarantee us.  Useful for
 * resource counting etc..
 */

#define ATOMIC_INIT(i)	{ (i) }

/**
 * atomic_read - read atomic variable
 * @v: pointer of type atomic_t
 *
 * Atomically reads the value of @v.
 */
static inline int atomic_read(const atomic_t *v)
{
	return ACCESS_ONCE((v)->counter);
}

/**
 * atomic_set - set atomic variable
 * @v: pointer of type atomic_t
 * @i: required value
 *
 * Atomically sets the value of @v to @i.
 */
static inline void atomic_set(atomic_t *v, int i)
{
	v->counter = i;
}

/**
 * atomic_add - add integer to atomic variable
 * @i: integer value to add
 * @v: pointer of type atomic_t
 *
 * Atomically adds @i to @v.
 */
static inline void atomic_add(int i, atomic_t *v)
{
	asm volatile(LOCK_PREFIX "addl %1,%0"
		     : "+m" (v->counter)
		     : "ir" (i));
}

/**
 * atomic_sub - subtract integer from atomic variable
 * @i: integer value to subtract
 * @v: pointer of type atomic_t
 *
 * Atomically subtracts @i from @v.
 */
static inline void atomic_sub(int i, atomic_t *v)
{
	asm volatile(LOCK_PREFIX "subl %1,%0"
		     : "+m" (v->counter)
		     : "ir" (i));
}

/**
 * atomic_inc - increment atomic variable
 * @v: pointer of type atomic_t
 *
 * Atomically increments @v by 1.
 */
static inline void atomic_inc(atomic_t *v)
{
	asm volatile(LOCK_PREFIX "incl %0"
		     : "+m" (v->counter));
}

/**
 * atomic_dec - decrement atomic variable
 * @v: pointer of type atomic_t
 *
 * Atomically decrements @v by 1.
 */
static inline void atomic_dec(atomic_t *v)
{
	asm volatile(LOCK_PREFIX "decl %0"
		     : "+m" (v->counter));
}

/**
 * atomic_inc_short - increment of a short integer
 * @v: pointer to type int
 *
 * Atomically adds 1 to @v
 * Returns the new value of @u
 */
static inline short int atomic_inc_short(short int *v)
{
	asm(LOCK_PREFIX "addw $1, %0" : "+m" (*v));
	return *v;
}

/* These are x86-specific, used by some header files */
#define atomic_clear_mask(mask, addr)				\
	asm volatile(LOCK_PREFIX "andl %0,%1"			\
		     : : "r" (~(mask)), "m" (*(addr)) : "memory")

#define atomic_set_mask(mask, addr)				\
	asm volatile(LOCK_PREFIX "orl %0,%1"			\
		     : : "r" ((unsigned)(mask)), "m" (*(addr))	\
		     : "memory")

#endif /* _ASM_X86_ATOMIC_H */