It seems you need to allocate the memory in the user space then you pass the pointer to the kernel space for the copy_to_user().
It would be nice if someone can point me to this kind allocate_in_kernel_for_user memory allocation facility.
David
Mandeep S. Brar wrote:
hi,
I am a newbie into linux programming. Ps help me with a small problem i am
facing while writing a sample program for a driver module.
I have a structure like
struct devstruct {
char* string;
int len;
};
I want to return information from the driver to a user process which queries
me with ioctl. The code has the following outline...
USER PROCESS
...........
struct devstruct var;
ioctl(fd, READ_COMMAND, &var);
printf("%s",var.string);
.....................
DRIVER Module
char* data="hello";
int len=5;
int myioctl (struct inode *inode, struct file *filp, unsigned int cmd,
unsigned long arg){
switch(cmd) {
.............
case READ_COMMAND: {
.....
struct devstruct* var = (struct
devstruct*)arg;
var->len = len;
/*********
allocate memory in user space?
**********/
var->string = (allocate memory = len+1 in
user space)
copy_to_user(var->string,data,len+1);
.....
}
break;
.............
}
}
My question is that how do i allocate memory in user space when i am in
kernel space or will copy_to_user do it automatically?. is there a variant
of kmalloc or what??
Thanks in advance
Mandeep
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