PATCH: default number of netloop devices to number of network devices

[Eric Schwartz <eric.schwartz@hp.com>]

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Right now, unless specifically overridden, loopback_init() in 
drivers/xen/netback/loopback.c creates 4 netloop devices.  If your 
default network device is eth4 or higher, you're out of luck creating a 
xenbrN device with /etc/xen/scripts/network-bridge unless you explicitly 
set netloop.nloopbacks to something higher.  This patch attempts to set 
a more reasonable default: the number of network devices that exist, as 
reported by dev_get_by_index().

This isn't a perfect solution-- in particular, there will generally be a 
few more devices than there are physical network devices, but looking 
around and consulting with Paul Moore (netlabel maintainer), there 
doesn't seem to be a good way to tell real network devices from pseudo 
ones.  My initial attempt at a patch checked tmp->name for whether it 
began with 'eth', but it's completely reasonable to have network devices 
named anything-- an old laptop used to have its wireless interface named 
'ath0', for instance, and another used 'wlan0'.  So while this approach 
may waste a little bit of memory, at module load time, we can ensure 
that no matter how many devices you have in your system, at least at 
boot time, you can create that many xenbrN devices.

Signed-off-by: Eric Schwartz <eric.schwartz@hp.com>

-=Eric

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--- linux-2.6.18.ia64/drivers/xen/netback/loopback.c.old	2007-10-25 13:05:30.716516696 -0400
+++ linux-2.6.18.ia64/drivers/xen/netback/loopback.c	2007-10-25 14:14:07.835744809 -0400
@@ -298,9 +298,18 @@
 static int __init loopback_init(void)
 {
 	int i, err = 0;
+	struct net_device *tmp;
 
-	if (nloopbacks == -1)
-		nloopbacks = is_initial_xendomain() ? 4 : 0;
+	if (nloopbacks == -1) {
+		nloopbacks = 0;
+
+		if (is_initial_xendomain()) {
+			for(i = 1; tmp = dev_get_by_index(i); i++) {
+				nloopbacks++;
+				dev_put(tmp);
+			} 
+		} 
+	}
 
 	for (i = 0; i < nloopbacks; i++)
 		if ((err = make_loopback(i)) != 0)

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