On Wed, Nov 27, 2013 at 9:57 PM, 乃宏周 <naive231@gmail.com> wrote:

In module code:
unsigned char buf[20];
struct file *device;

device = filp_open(...);
device->f_op->read(device,buf,20,&device->f_pos);

In signature(interface) of read() of struct file, buf should came from user-space. I fed my buffer, and I get correct data from that, Is that correct? Shouldn't I provide a user-space buffer to that ?

Some convention in kernel programming:

long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)

{

here __user is used for declaration - explicitly saying that the pointer is pointing to userspace data.

without it, all pointer necessarily need to point to kernel allocated memory, and u used copy_from_user() to copy data from userspace to kernel pointer.

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Regards,
Peter Teoh