As i know, you have to allocate memory either statically or dynamically
in user space for var.string and pass pointer thro. ioctl.
copy_to_user() is not going to allocate memory, it just copies data from
kernel space to user space.
Ensure that allocated memory for string member will always be more than
len+1 (of kernel) to avoid memory corruption.
Regards,
Madhu
On Thu, 16 Jan 2003, 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
>
>
> --
> Kernelnewbies: Help each other learn about the Linux kernel.
> Archive: http://mail.nl.linux.org/kernelnewbies/
> FAQ: http://kernelnewbies.org/faq/
>
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