​【深入理解Linux内核锁】| 原子操作

/*设置原子变量的值*/
atomic_t v = ATOMIC_INIT(0);            /* 定义原子变量v并初始化为0 */
void atomic_set(atomic_t *v, int i);    /* 设置原子变量的值为i */
<p>/<em>获取原子变量的值</em>/
atomic_read(atomic_t <em>v);          /</em> 返回原子变量的值*/</p><p>/<em>原子变量的加减</em>/
void atomic_add(int i, atomic_t <em>v);      /</em> 原子变量增加i <em>/
void atomic_sub(int i, atomic_t </em>v);      /<em> 原子变量减少i </em>/</p><p>/<em>原子变量的自增，自减</em>/
void atomic_inc(atomic_t <em>v);    /</em> 原子变量增加1 <em>/
void atomic_dec(atomic_t </em>v);        /<em> 原子变量减少1 </em>/</p><p>/<em>原子变量的操作并测试</em>/
int atomic_inc_and_test(atomic_t <em>v);  /</em>进行对应操作后，测试原子变量值是否为0<em>/
int atomic_dec_and_test(atomic_t </em>v);
int atomic_sub_and_test(int i, atomic_t *v);</p><p>/<em>原子变量的操作并返回</em>/
int atomic_add_return(int i, atomic_t <em>v); /</em>进行对应操作后，返回新的值<em>/
int atomic_sub_return(int i, atomic_t </em>v);
int atomic_inc_return(atomic_t <em>v);
int atomic_dec_return(atomic_t </em>v);

typedef struct {<br />
int counter;
} atomic_t;

#define ATOMIC_INIT(i) { (i) }

#define atomic_set(v,i) WRITE_ONCE(((v)->counter), (i))</p><h1>define WRITE_ONCE(x, val) \</h1><p>({       \
union { typeof(x) <strong>val; char </strong>c[1]; } <strong>u = \
{ .</strong>val = (<strong>force typeof(x)) (val) }; \
</strong>write_once_size(&(x), <strong>u.</strong>c, sizeof(x)); \
<strong>u.</strong>val;     \
})
static <strong>always_inline void <strong>write_once_size(volatile void <em>p, void </em>res, int size)
{
switch (size) {
case 1: *(volatile </strong>u8 <em>)p = </em>(<strong>u8 <em>)res; break;
case 2: </em>(volatile </strong>u16 <em>)p = </em>(<strong>u16 <em>)res; break;
case 4: </em>(volatile </strong>u32 <em>)p = </em>(<strong>u32 <em>)res; break;
case 8: </em>(volatile </strong>u64 <em>)p = </em>(<strong>u64 *)res; break;
default:
barrier();
</strong>builtin_memcpy((void <em>)p, (const void </em>)res, size);
barrier();
}
}

/* </p><ul><li>ARMv6 UP and SMP safe atomic ops.  We use load exclusive and </li><li>store exclusive to ensure that these are atomic.  We may loop </li><li>to ensure that the update happens. 
*/<h1>define ATOMIC_OP(op, c_op, asm_op)     \</h1><p>static inline void atomic_##op(int i, atomic<em>t *v)   \
{         \
unsigned long tmp;      \
int result;       \
\
prefetchw(&v->counter);      \
<strong>asm</strong> <strong>volatile</strong>("@ atomic</em>" #op "\n"   \
"1: ldrex %0, [%3]\n"      \
" " #asm_op " %0, %0, %4\n"     \
" strex %1, %0, [%3]\n"      \
" teq %1, #0\n"      \
" bne 1b"       \
: "=&r" (result), "=&r" (tmp), "+Qo" (v->counter)  \
: "r" (&v->counter), "Ir" (i)     \
: "cc");       \
}         </p><h1>define ATOMIC_OP_RETURN(op, c_op, asm_op)    \</h1><p>static inline int atomic_##op##_return_relaxed(int i, atomic<em>t *v) \
{         \
unsigned long tmp;      \
int result;       \
\
prefetchw(&v->counter);      \
\
<strong>asm</strong> <strong>volatile</strong>("@ atomic</em>" #op "_return\n"  \
"1: ldrex %0, [%3]\n"      \
" " #asm_op " %0, %0, %4\n"     \
" strex %1, %0, [%3]\n"      \
" teq %1, #0\n"      \
" bne 1b"       \
: "=&r" (result), "=&r" (tmp), "+Qo" (v->counter)  \
: "r" (&v->counter), "Ir" (i)     \
: "cc");       \
\
return result;       \
}</p><h1>define ATOMIC_FETCH_OP(op, c_op, asm_op)    \</h1><p>static inline int atomic<em>fetch</em>##op##_relaxed(int i, atomic_t *v) \
{         \
unsigned long tmp;      \
int result, val;      \
\
prefetchw(&v->counter);      \
\
<strong>asm</strong> <strong>volatile</strong>("@ atomic<em>fetch</em>" #op "\n"   \
"1: ldrex %0, [%4]\n"      \
" " #asm_op " %1, %0, %5\n"     \
" strex %2, %1, [%4]\n"      \
" teq %2, #0\n"      \
" bne 1b"       \
: "=&r" (result), "=&r" (val), "=&r" (tmp), "+Qo" (v->counter) \
: "r" (&v->counter), "Ir" (i)     \
: "cc");       \
\
return result;       \
}</p><h1>define ATOMIC_OPS(op, c_op, asm_op)     \</h1><p>ATOMIC_OP(op, c_op, asm_op)     \
ATOMIC_OP_RETURN(op, c_op, asm_op)    \
ATOMIC_FETCH_OP(op, c_op, asm_op)

ATOMIC_OPS(add, +=, add)
ATOMIC_OPS(sub, -=, sub)

void set_bit(nr, void <em>addr);  // 设置位：将addr地址的第nr位设置为1
void clear_bit(nr, void </em>addr);  // 清除位：将addr地址的第nr位设置为0
void change_bit(nr, void <em>addr); // 改变位：对addr地址的第nr位进行反置。
test_bit(nr, void </em>addr);   // 测试位：返回addr地址的第nr位。
int test_and_set_bit(nr, void <em>addr); // 测试并设置位
int test_and_clear_bit(nr, void </em>addr); // 测试并清除位
int test_and_change_bit(nr, void *addr); // 测试并改变位

#define set_bit(nr,p)   ATOMIC_BITOP(set_bit,nr,p)</p><h1>define ATOMIC_BITOP(name,nr,p)   \</h1><p>(<strong>builtin_constant_p(nr) ? __</strong>atomic<em>##name(nr, p) : </em>##name(nr,p))
extern void _set_bit(int nr, volatile unsigned long <em> p);
/</em> </p></li><li>These functions are the basis of our bit ops. </li><li></li><li>First, the atomic bitops. These use native endian. 
<em>/
static inline void ____atomic_set_bit(unsigned int bit, volatile unsigned long </em>p)
{
unsigned long flags;
unsigned long mask = BIT_MASK(bit);
p += BIT_WORD(bit);
raw_local_irq_save(flags);
*p |= mask;
raw_local_irq_restore(flags);
}<h1>define BIT_MASK(nr)  (1UL