copy_from_user(to, from, n)

/*include\asm-mips\Uaccess.h*/

/*
* copy_from_user: - Copy a block of data from user space.
* @to:   Destination address, in kernel space.
* @from: Source address, in user space.
* @n:    Number of bytes to copy.
*
* Context: User context only. This function may sleep.
*
* Copy data from user space to kernel space.
*
* Returns number of bytes that could not be copied.
* On success, this will be zero.
*
* If some data could not be copied, this function will pad the copied
* data to the requested size using zero bytes.
*/

#define copy_from_user(to, from, n)      \
({          \
void *__cu_to;        \
const void __user *__cu_from;      \
long __cu_len;        \
          \
might_sleep();        \
__cu_to = (to);        \
__cu_from = (from);       \
__cu_len = (n);        \
if (access_ok(VERIFY_READ, __cu_from, __cu_len))   \
   __cu_len = __invoke_copy_from_user(__cu_to, __cu_from, \
                                     __cu_len);   \
__cu_len;        \
})

昨天在接触CC2500 Device Driver时,在应用程序(用户空间中)向内核写入一数据时,需要调用copy_from_user来传递,可是发现传不过来...

通过在用户空间获得errno,提示Bad Address

后来发现在使用copy_from_user时,需要对其返回作下判断就可以了...

之前代码:

内核空间:

if(!copy_from_user(tmpbuf, buf, count))
   return -EFAULT;

用户空间:

write(CC2500_Fd, buf, count);

printf(" errno = %s\n", strerror(errno));

此时会显示errno = Bad Address,无法向内核空间写入数据,也即无法在内核空间向下进展了

之后代码:

ret = copy_from_user(tmpbuf, buf, count);

if(ret != 0)

    return -EFAULT;

用户空间:

write(CC2500_Fd, buf, count);

printf(" errno = %s\n", strerror(errno));

此时显示errno = Success,从用户空间成功的向内核空间内写入数据了