[libvirt] libvirt 0.6.4: Confusing error message during virDomainRestore() if network not started

[Charles Duffy]

Howdy, 'yall -- I found myself scratching my head for a few minutes 
trying to start a VM image via virDomainRestore().

Looking through the header definition in the XML, it read as follows:

     <interface type="network">
       <mac address="00:15:3d:49:ec:0e"/>
       <source network="fvte-MIXED-DEFAULT"/>
       <target dev="vnet3"/>
       <model type="e1000"/>
     </interface>

...and on trying to do a virDomainRestore(), it exited with the following:

Traceback (most recent call last):
   File "/usr/bin/fvte", line 8, in <module>
     load_entry_point('fvte==1.0', 'console_scripts', 'fvte')()
   File "/local/home-aux/cduffy/public_git/fvte/src/m1/fvte/cli.py", 
line 1838, in main
     cli.cmdloop()
   File "/opt/python25/lib/python2.5/cmd.py", line 142, in cmdloop
     stop = self.onecmd(line)
   File "/local/home-aux/cduffy/public_git/fvte/src/m1/fvte/cli.py", 
line 1791, in onecmd
     cmd.Cmd.onecmd(self, c)
   File "/opt/python25/lib/python2.5/cmd.py", line 219, in onecmd
     return func(arg)
   File "/local/home-aux/cduffy/public_git/fvte/src/m1/fvte/cli.py", 
line 1538, in do_mode
     self._vmm.vh_set_runmode(name, desired)
   File "/local/home-aux/cduffy/public_git/fvte/src/m1/fvte/vmmanip.py", 
line 324, in vh_set_runmode
     succp = (0 == virt['connect'].restore(ramfile))
   File "/opt/python25/lib/python2.5/site-packages/libvirt.py", line 
1224, in restore
     if ret == -1: raise libvirtError ('virDomainRestore() failed', 
conn=self)
libvirt.libvirtError: internal error Failed to add tap interface 
'vnet%d' to bridge 'fvtebr0' : No such device

The actual issue was that the fvte-MIXED-DEFAULT network was not 
running, and an appropriate "virsh net-start" allowed the domain to 
restore correctly; detecting this condition and providing a clearer 
error message would probably be a Good Thing.