Linux Ethernet Bridging - Apr 2007 - [Bridge] Little problem with 1.x versions (if_indextoname)

Hi, 
I have used bridge-utils 0.9.6 so far in a kernel 2.4.26, uClibc and ppc
environment.

When I use version 1.0.3 I have the problem that I do not see the brige with the
'brctl show' command if it is not fully set up. It was working with
0.9.6.
I tracked the problem down to an 'incompatibility' in
bridge/uClibc/kernel.

0.9.6 uses its own if_indextoname function which uses the SIOCGIFNAME ioctl
which works with the kernel.
Version 1.x uses the libc if_indextoname (here uClibc) which uses the
SIOCGIFCONF ioctl and scans the if list to resolv the name for an if_index.
The kernel will not send back interfaces which do not have an ip address (or
exactly only for protocol family inet or decnet).
So if the bridge does not have an ip address the name resolution fails and
old_foreach_bridge() fails as well.

I'm not sure who has the problem now (kernel, uClibc, bridge) , but I think
I will insert if_indextoname() back to the bridge.

I hope that this information is useful.

Regards
Harald K?the

On Thu, 03 Jun 2004 09:37:34 +0200
"Harald K?the" <Harald.Kuethe@controlware.de> wrote:
> Hi, 
> I have used bridge-utils 0.9.6 so far in a kernel 2.4.26, uClibc and ppc
environment.
> 
> When I use version 1.0.3 I have the problem that I do not see the brige
with the 'brctl show' command if it is not fully set up. It was working
with 0.9.6.
> I tracked the problem down to an 'incompatibility' in
bridge/uClibc/kernel.
> 
> 0.9.6 uses its own if_indextoname function which uses the SIOCGIFNAME ioctl
which works with the kernel.
> Version 1.x uses the libc if_indextoname (here uClibc) which uses the
SIOCGIFCONF ioctl and scans the if list to resolv the name for an if_index.
> The kernel will not send back interfaces which do not have an ip address
(or exactly only for protocol family inet or decnet).
> So if the bridge does not have an ip address the name resolution fails and
old_foreach_bridge() fails as well.
> 
> I'm not sure who has the problem now (kernel, uClibc, bridge) , but I
think I will insert if_indextoname() back to the bridge.
> 
> I hope that this information is useful.
> 
> Regards
> Harald K?the
Rather than copy more code back into the bridge-utilities, how about applying
this
change to uClibc?  I hate when packages get cluttered for workarounds for other
incompatibilities.

The problem is that SIOCGIFCONF only lists interfaces that have IP addresses, so
it
doesn't find the other interfaces that are being used for bridging. It could
be fixed
in the kernel to return all interfaces, but then something else might break; and
still
it mean a kernel update for the 2.4 users. 

The whole use of ifindex in the bridge API is a bad idea. But we probably have
to live
with it for compatibility.

Patch against uClibc 0.9.26
------------------------------------------------------------
--- if_nametoindex.c.orig	2002-12-04 10:27:15.000000000 -0800
+++ if_nametoindex.c	2004-06-03 10:31:34.732707064 -0700
@@ -148,6 +148,27 @@
 
 char * if_indextoname (unsigned int ifindex, char *ifname)
 {
+#ifdef SIOCGIFNAME
+  /* Use ioctl to avoid searching the list. */
+  struct ifreq ifr;
+  int fd, saved_errno;
+
+  fd = __opensock ();
+  
+  if (fd < 0)
+      return NULL;
+
+  ifr.ifr_ifindex = ifindex;
+  if (ioctl (fd, SIOCGIFNAME, &ifr) < 0) {
+      saved_errno = errno;
+      close (fd);
+      __set_errno (saved_errno);
+      return NULL;
+  }
+  close (fd);
+
+  return strncpy (ifname, ifr.ifr_name, IFNAMSIZ);
+#else
     struct if_nameindex *idx;
     struct if_nameindex *p;
     char *result = NULL;
@@ -163,5 +184,6 @@
 	if_freenameindex (idx);
     }
     return result;
+#endif
 }