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On Fri, 20 Jun 2003 21:17:52 +0200
Daniele Bellucci <bellucda@tiscali.it> wrote:
>Hi,
>i'm trying to make a simple hack to my e100 netdriver.... but i've a problem:
>i need to understand what does "ifconfig eth0 up" performs...
Let's take a look at what happens.
When you do "ifconfig eth0 up" a simple strace(8) tracing tells you a
ioctl(SIOCSIFFLAGS) starts. This is useful for setting IFF_UP flag in dev->flag.
What's important to realize is what really happens (please take net/core/dev.c
handy).
In dev_ioctl() you can see
case SIOCSIFFLAGS:
if (!capable(CAP_NET_ADMIN))
return -EPERM;
dev_load(ifr.ifr_name);
dev_probe_lock();
rtnl_lock();
ret = dev_ifsioc(&ifr, cmd);
rtnl_unlock();
dev_probe_unlock();
return ret;
Let's take a look at dev_ifsioc().
case SIOCSIFFLAGS: /* Set interface flags */
return dev_change_flags(dev, ifr->ifr_flags);
And now the really interesting part of dev_change_flags()
int old_flags = dev->flags;
/*
* Set the flags on our device.
*/
dev->flags = (flags & (IFF_DEBUG|IFF_NOTRAILERS|IFF_NOARP|
IFF_DYNAMIC| IFF_MULTICAST|IFF_PORTSEL|
IFF_AUTOMEDIA)) | (dev->flags & (IFF_UP|
IFF_VOLATILE|IFF_PROMISC|IFF_ALLMULTI));
/*
* Load in the correct multicast list now the flags have changed.
*/
dev_mc_upload(dev);
/*
* Have we downed the interface. We handle IFF_UP ourselves
* according to user attempts to set it, rather than blindly
* setting it.
*/
ret = 0;
if ((old_flags^flags)&IFF_UP) /* Bit is different ? */
{
ret = ((old_flags & IFF_UP) ? dev_close : dev_open)(dev);
if (ret == 0)
dev_mc_upload(dev);
}
Please take a look here. As you can see, if IFF_UP was not set (if down),
what happens is simply
ret = dev_open(dev);
and if you look at dev_open()
if (dev->open) {
ret = dev->open(dev);
so it calls the interface open method thus 'opening' your NIC. The open
method usually requests an IRQ and register it and does few other things.
Similarly, when you clear IFF_UP the interface close method is called.
Take a look at dev.c please. You can find anything there.
>I need to know what syscalls are needed to "wakeup"/setup a net link....
> i suppose that an ioctl cmd is needed ... but i can't understand what
> should be open in /dev ....
Network interfaces do not use dev special files but they are maintained by
the kernel through struct netdevice's linked through a global linked list.
Ciao.
- --
Angelo Dell'Aera 'buffer'
Antifork Research, Inc. http://buffer.antifork.org
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