Daniel P. Berrange wrote: >For the QEMU / KVM driver, if the user doesn't specify an explicit name for >the TAP device associated with a virtual NIC, we auto-generate one with a >name vnetXXX. You can see this if you dump XML for a running QEMU guest. >Unfortunately if you dump XML, make a change and then feed it back in with >the define XML API, you have now persisted this auto-generated VIF name. > >Do this for several domains at varying times and you'll eventually get >2 domains which have persisted the same auto-generated vnetXXX device >name. You can now not start both of these VMs at once. > >The fix for this is simple - simply strip any TAP device name starting with >the string 'vnet' when defining a new VM. It will thus get assigned a new >automatically generate name which doesn't clash. The patch also strips out >hardcoded vnetXXX names when starting a VM to proactively deal with any >existing VMs whose config has been broken in this way. Hang about though, don't we sometimes want to explicitly set the name of some interfaces to vnetXXX?

On Tue, Dec 04, 2007 at 05:40:44PM +0000, Richard W.M. Jones wrote: > Daniel P. Berrange wrote: > >For the QEMU / KVM driver, if the user doesn't specify an explicit name for > >the TAP device associated with a virtual NIC, we auto-generate one with a > >name vnetXXX. You can see this if you dump XML for a running QEMU guest. > >Unfortunately if you dump XML, make a change and then feed it back in with > >the define XML API, you have now persisted this auto-generated VIF name. > > > >Do this for several domains at varying times and you'll eventually get > >2 domains which have persisted the same auto-generated vnetXXX device > >name. You can now not start both of these VMs at once. > > > >The fix for this is simple - simply strip any TAP device name starting with > >the string 'vnet' when defining a new VM. It will thus get assigned a new > >automatically generate name which doesn't clash. The patch also strips out > >hardcoded vnetXXX names when starting a VM to proactively deal with any > >existing VMs whose config has been broken in this way. > > Hang about though, don't we sometimes want to explicitly set the name of > some interfaces to vnetXXX? No, if you want to manually set interface names, you have to use something other than a 'vnet' prefix. 'vnet' is the prefix for auto-generated names in same way as 'vif' is the prefix for Xen auto-generated names.