netdev - Re: Get the IP address of an interface with a given name

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Date:	Tue, 20 Nov 2007 15:00:48 +0200
From:	"Rami Rosen" <roszenrami@...il.com>
To:	Giacomo <delleceste@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Get the IP address of an interface with a given name

Giacomo,

  Consider using the dev_get_by_name/() kernel method; this is a
simplified example which works with device named "eth0" :

  struct net_device* device;
  struct in_device* in_dev;
  struct in_ifaddr* if_info;

  device = dev_get_by_name("eth0");
  in_dev = (struct in_device *)device->ip_ptr;
  if_info = in_dev->ifa_list;
	for (;if_info;if_info=if_info->ifa_next)
		{
		if (!(strcmp(if_info->ifa_label,"eth0")))
			{
			printk("if_info->ifa_address=%x\n",if_info->ifa_address);	
			break;
			}
		}


Yous should of course add check for NULL, etc.

Regards,
Rami Rosen


On Nov 20, 2007 10:09 AM, Giacomo <delleceste@...il.com> wrote:
> Good morning.
>
>  I have written a kernel function which needs to get the IP address of
> an active network interface
>  given its name.
>
>  The actual implementation i have done is like this
>  but i suspect this does not always work.
>  Is there any API already provided by the kernel to do the same?
>
>  Thanks a lot
>
>  Giacomo
>
>  -- actual implementation: ---
>
>  /* returns in *addr the internet address having the name ifname */
>  int get_ifaddr_by_name(const char *ifname, __u32 * addr)
>  {
>         struct net_device *pnet_device;
>         struct in_device *pin_device;
>         struct in_ifaddr* inet_ifaddr;
>
>         read_lock_bh(&dev_base_lock);
>  #if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,22)
>         pnet_device = dev_base;
>  #else
>         pnet_device = first_net_device();
>  #endif
>         while (pnet_device != NULL)
>         {
>                 if ((netif_running(pnet_device))
>                                 && (pnet_device->ip_ptr != NULL)
>                                 && (strcmp(pnet_device->name, ifname) == 0))
>                 {
>                         pin_device =
>                                 (struct in_device *) pnet_device->ip_ptr;
>                         inet_ifaddr = pin_device->ifa_list;
>                         if(inet_ifaddr == NULL)
>                         {
>                                 printk("ifa_list is null!\n");
>                                 break;
>                         }
>                         /* ifa_local: ifa_address is the remote point in ppp */
>                         *addr = (inet_ifaddr->ifa_local);
>                           read_unlock_bh(&dev_base_lock);
>                         return 1;
>                 }
>  #if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,22)
>                 pnet_device = pnet_device->next;
>  #else
>                 pnet_device = next_net_device(pnet_device);
>  #endif
>
>         }
>
>         read_unlock_bh(&dev_base_lock);
>         return -1;              /* address not found! */
>  }
>
> --
> Giacomo S.
> http://www.giacomos.it
>
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>
> IPFIREwall (http://www.giacomos.it/ipfire) viene presentato
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> Linux Day 2006:
> http://iglu.cc.uniud.it/linuxday
>
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