Re: [libvirt] [Qemu-devel] Problems using netdev_del+netdev_add w/o corresponding device_del+device_add

On Sat, Oct 13, 2012 at 04:47:14PM -0400, Laine Stump wrote: > Here is the sequence sent to disconnect only the host side, then > reconnect it with a new tap device. (although the fd is the same, this > is because the old tap device had already been closed, so the number is > just being used - the same thing happens when doing sequential full > detach/attach cycles, and they all work with no problems): > > > 168.750 > 0x7f8e20000c90 > {"execute":"netdev_del","arguments":{"id":"hostnet0"},"id":"libvirt-30"} > 168.762 < 0x7f8e20000c90 {"return": {}, "id": "libvirt-30"} > 168.800 > 0x7f8e20000c90 > {"execute":"getfd","arguments":{"fdname":"fd-net0"},"id":"libvirt-31"} > (fd=27) > 168.801 < 0x7f8e20000c90 {"return": {}, "id": "libvirt-31"} > 168.801 > 0x7f8e20000c90 > {"execute":"netdev_add","arguments":{"type":"tap","fd":"fd-net0","id":"hostnet0"},"id":"libvirt-32"} > 168.802 < 0x7f8e20000c90 {"return": {}, "id": "libvirt-32"} > 168.802 > 0x7f8e20000c90 > {"execute":"set_link","arguments":{"name":"net0","up":true},"id":"libvirt-33"} > 168.803 < 0x7f8e20000c90 {"return": {}, "id": "libvirt-33"} > > After this sequence is done, everything about the network device > *appears* normal on both the guest and host (at least the things I know > to look at), but no traffic from the host shows up in a tcpdump of the > interface on the guest, and no traffic from the guest shows up in a > tcpdump of the tap device on the host. What you are trying to do isn't possible today. The device associates with the netdev during initialization only - there is no command to associate at a later point in time. That is why your example works only when the device is deleted together with the netdev. It is certainly possible to implement a command to switch netdevs but I'm curious what the use case is. Is this necessary just because QEMU doesn't provide a way to modify the existing netdev or because you really want to switch to a completely different netdev?