Question about copy_from_user/copy_to_user

[Qiuyu Zhang <qiuyu.zhang@gmail.com>]

Hi all,

I am working on a module driver. A user application alloc a bunch of
memory for storing packet. And module driver can read /write data
from/into the memory in user space. I use ioctl function to pass the
pointer of memory of user space to module driver.  What I want to do
is to store the pointer in kernel space and when I need to write or
read data from memory of user space, I try to use copy_from_user or
copy_to_user to get/put data. But I always get wrong data. I don't
know the reason. Would you guys give me some help?

Simple description of the code:

device_ioctl() {
     // get the pointer of memory of user space, and assign the
pointer to kernel variable.
}



device_xmit(){
     // when upper layer send a packet to this device.
     //  I try to use the copy_from_user to get some information from
user space buf
     // but I cannot get correct information.   
}

Thx