give a more useful diagnostic for tap-add failure w/ENOTSUP

* src/qemu_conf.c (qemudNetworkIfaceConnect):
Suggestion from Daniel P. Berrange.

ChangeLog

+Wed Jul  9 07:23:31 CEST 2008 Jim Meyering <meyering@redhat.com>
+
+	give a more useful diagnostic for tap-add failure w/ENOTSUP
+	* src/qemu_conf.c (qemudNetworkIfaceConnect):
+	Suggestion from Daniel P. Berrange.
+
 Tue Jul  8 18:47:56 BST 2008 Daniel P. Berrange <berrange@redhat.com>
 
 	* src/xs_internal.c: Fix typo in domain state constant (Toth
@@ -49,7 +55,7 @@ Fri Jun 27 15:05:31 PDT 2008 Dan Smith <danms@us.ibm.com>
 	Fix compiler warnings in LXC
 	* src/veth.c: remove unused and fix uninitialized variable
 
-Thu Jun 26 19:51:19 JST 2008 Atsushi SAKAI <sakaia@jp.fujitsu.com> 
+Thu Jun 26 19:51:19 JST 2008 Atsushi SAKAI <sakaia@jp.fujitsu.com>
 
 	fix make syntax-check
 	* src/xm_internal.c: replace tabs to spaces

src/qemu_conf.c

@@ -2304,9 +2304,17 @@ qemudNetworkIfaceConnect(virConnectPtr conn,
 
     if ((err = brAddTap(driver->brctl, brname,
                         ifname, BR_IFNAME_MAXLEN, &tapfd))) {
-        qemudReportError(conn, NULL, NULL, VIR_ERR_INTERNAL_ERROR,
-                     _("Failed to add tap interface '%s' to bridge '%s' : %s"),
-                         ifname, brname, strerror(err));
+        if (errno == ENOTSUP) {
+            /* In this particular case, give a better diagnostic. */
+            qemudReportError(conn, NULL, NULL, VIR_ERR_INTERNAL_ERROR,
+                             _("Failed to add tap interface to bridge. "
+                               "%s is not a bridge device"), brname);
+        } else {
+            qemudReportError(conn, NULL, NULL, VIR_ERR_INTERNAL_ERROR,
+                             _("Failed to add tap interface '%s' "
+                               "to bridge '%s' : %s"),
+                             ifname, brname, strerror(err));
+        }
         goto error;
     }