> I have two structures that i share between kernel/userspace as
> follows:
>
> struct foo {
> int num;
> struct bar *bartable;
> };
>
> struct bar {
> u32 ipaddr;
> unsigned char mac_addr[6];
> };
> The ioctl
> handling routine in the kernel is as follows:
> --
> struct foo fookern;
> struct foo *userinfo = (struct foo *)ifr->ifr_data;
> struct bar *entry;
>
> copy_from_user(&fookern, userinfo, sizeof(struct foo));
>
> for(i=0, entry = fookern.bartable; i < fookern.num; i++, entry++) {
> print(entry->ipaddr, entry->mac_addr) // pseudo code
> }
> --
>
> The complete table calloc'ed to 'bartable' and initialized in the
> userspace is not reflected in the kernel. Printing entry->ipaddr and
> entry->mac_addr 'fookern.num' times prints all entry->ipaddr entries
Are you sure this prints the right values? After the copy_from_user(),
fookern.bartable still points to a userland address. How can you
dereference it in the kernel?
> So, how can be correctly copy pointer variables from userspace to
> kernelspace? Or should there be a change in the sizeof parameter in
> the copy_from_user() call?
You need a second copy_from_user() to copy data that the pointer
variable refers to. In your example, you'd need to copy in
sizeof(struct bar) bytes from each fookern.bartable pointer.
Hope this helps,
Ravi.
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