- Provides a means for the administrator to execute an arbitrary script
- to connect the guest's network to the LAN. The guest will have a tun
- device created with a name of vnetN, which can also be overridden with the
- <target> element. After creating the tun device a shell script will
- be run which is expected to do whatever host network integration is
- required. By default this script is called /etc/qemu-ifup but can be
- overridden.
+ Provides a means to use a new or existing tap device (or veth
+ device pair, depening on the needs of the hypervisor driver)
+ that is partially or wholly setup external to libvirt (either
+ prior to the guest starting, or while the guest is being started
+ via an optional script specified in the config).
+
+
+ The name of the tap device can optionally be specified with
+ the dev attribute of the
+ <target> element. If no target dev is
+ specified, libvirt will create a new standard tap device with a
+ name of the pattern "vnetN", where "N" is replaced with a
+ number. If a target dev is specified and that device doesn't
+ exist, then a new standard tap device will be created with the
+ exact dev name given. If the specified target dev does exist,
+ then that existing device will be used. Usually some basic setup
+ of the device is done by libvirt, including setting a MAC
+ address, and the IFF_UP flag, but if the dev is a
+ pre-existing device, and the managed attribute of
+ the target element is also set to "no" (the default
+ value is "yes"), even this basic setup will not be performed -
+ libvirt will simply pass the device on to the hypervisor with no
+ setup at all. Since 5.7.0 Using
+ managed='no' with a pre-created tap device is useful because
+ it permits a virtual machine managed by an unprivileged libvirtd
+ to have emulated network devices based on tap devices.
+
+
+ After creating/opening the tap device, an optional shell script
+ (given in the path attribute of
+ the <script> element) will be run; this can
+ be used to do whatever extra host network integration is
+ required.