Hi
Thanks for the reply. I followed the same and found out that the
function devinet_ioctl() function does the configuration changes. This
function is defined in /usr/src/linux/net/ipv4/devinet.c
But if you the code it copies the contents from user space memory to
kernel space (copy_from_user). It would mean that I cannot call this
function from kernel space, as the buffer I would be passing would
definitely be in kernel space.
I cannot even use get_fs() and set_fs() (using get_ds()) and continue
calling the function because it is not always true that my module will
always be initated in process context.
Please comment if I am wrong.
Regards
bhaskar
On Wed, 2004-06-16 at 16:12, Jan Hudec wrote:
> On Wed, Jun 16, 2004 at 11:58:15 +0530, Bhaskar-ROCSYS wrote:
> > Hi all,
> >
> > Is there any way to create a dynamic interface from kernel space.
> >
> > Is it possible to change the parameters of an interface from kernel
> > space?
> >
> > All these can be done by using ifconfig. But I want to do it from
> > kernel space.
> > I want to change the IP address from kernel space and change the IP
> > address. I have written a small code to do this but i am not able to
> > see the effect.
>
> ifconfig obviously runs in userspace. So it can't touch the kernel
> varaibles. So it has to communicate the data somehow. Look how it works
> (strace will suffice -- you just need to know the syscalls it calls).
> Then read the code of those syscalls until you get past the
> copy_from_user stuff and basic sanity-checiking. Then call the function
> that does the works.
>
> > The code I had written is:
>
> > [...]
> > int init_module()
> > {
> > struct in_device *in_dev;
> > struct in_ifaddr **ifap = NULL;
> > struct in_ifaddr *ifa = NULL;
> > struct net_device *dev;
> >
> > if((dev = __dev_get_by_name("eth0")) == NULL)
> > {
> > printk("<1>Cannot get info for eth0\n");
> > return -1;
> > }
> >
> > if((in_dev = __in_dev_get(dev))!= NULL)
> > {
> > for (ifap=&in_dev->ifa_list; (ifa=*ifap) != NULL; ifap=&ifa->ifa_next)
> > {
> > if ((strcmp("eth0", ifa->ifa_label) == 0))
> > break; /* found */
> > }
> > }
> > if(ifa)
> > {
> > ifa->ifa_local = htonl(0xac100f63);
> >
> > ifa->ifa_prefixlen = 24;
> > ifa->ifa_mask = inet_make_mask(ifa->ifa_prefixlen);
> > if ((dev->flags&IFF_BROADCAST) && ifa->ifa_prefixlen <
> > 31)
> > ifa->ifa_broadcast =
> > ifa->ifa_address|~ifa->ifa_mask;
> > }
> > else printk("<1>Could not find the device\n");
> >
> > return 0;
> > }
> >
> > The changes are made but when I am trying to send packet its failing.
> >
> > Is there any other way to change the interface parameters from kernel
> > space ?
>
> It's likely harder than just changing the value. There might be other
> data structures, that need updating. Just read the code used by ifconfig
> to set it and call it or do the same.
>
> -------------------------------------------------------------------------------
> Jan 'Bulb' Hudec <bulb@ucw.cz>
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