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Until now, the "live" XML status of an <interface type='network'>
device would always show the network information, rather than the
exact hardware device that was used. It would also show the name of
any portgroup the interface belonged to, rather than providing the
configuration that was derived from that portgroup. As an example,
given the following network definition:
[A]
<network>
<name>testnet</name>
<forward type='bridge' dev='p4p1_0'>
<interface dev='p4p1_0'/>
<interface dev='p4p1_1'/>
<interface dev='p4p1_2'/>
<interface dev='p4p1_3'/>
</forward>
<portgroup name='admin'>
<bandwidth>
<inbound average='1000' peak='5000' burst='1024'/>
<outbound average='128' peak='256' burst='256'/>
</bandwidth>
</portgroup>
</network>
and the following domain <interface>:
[B]
<interface type='network'>
<source network='testnet' portgroup='admin'/>
</interface>
the output of "virsh dumpxml $domain" while the domain was running
would yield something like this:
[C]
<interface type='network'>
<source network='testnet' portgroup='admin'/>
<target dev='macvtap0'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
In order to learn the exact bandwidth information of the interface, a
management application would need to retrieve the XML for testnet,
then search for the portgroup named "admin". Even worse, there was no
simple and standard way to learn which host physdev the macvtap0
device is attached to.
Internally, libvirt has always kept this information in the
virDomainDef that is held in memory, as well as storing it in the
(libvirt-internal-only) domain status XML (in
/var/run/libvirt/qemu/$domain.xml). In order to not confuse the runtime
"actual state" with the config of the device, it's internally stored
like this:
[D]
<interface type='network'>
<source network='testnet' portgroup='admin'/>
<actual type='direct'>
<source dev='p4p1_0' mode='bridge'/>
<bandwidth>
<inbound average='1000' peak='5000' burst='1024'/>
<outbound average='128' peak='256' burst='256'/>
</bandwidth>
</actual>
<target dev='macvtap0'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
This was never exposed outside of libvirt though, because I thought it
would be too awkward for a management application to need to look in
two places for the same information, but I also wasn't sure that it
would be okay to overwrite the config info (in this case "<source
network='testnet' portgroup='admin'/>") with the actual runtime info
(everything inside <actual> above).
Now we have a need for this information to be made available to
management applications (in particular, so that a network "plugged"
hook will have full information about the device that is being plugged
in), so it's time to take the leap and decide that it is acceptable
for the config info to be replaced with actual runtime state (but
*only* when reporting domain live status, *not* when saving state in
/var/run/libvirt/qemu/$domain.xml - that remains the same so that
there is no loss of information). That is what this patch does - once
applied, the output of "virsh dumpxml $domain" when the domain is
running will contain something like this:
[E]
<interface type='direct'>
<source dev='p4p1_0' mode='bridge'/>
<bandwidth>
<inbound average='1000' peak='5000' burst='1024'/>
<outbound average='128' peak='256' burst='256'/>
</bandwidth>
<target dev='macvtap0'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
In effect, everything that is internally stored within <actual> is
moved up a level to where a management application will expect
it. This means that the management application will only look in a
single place to learn - the type of interface in use, the name of the
physdev (if relevant), the <bandwidth>, <vlan>, and <virtualport>
settings in use.
The potential downside is that a management app looking at this output
will not see that the physdev 'p4p1_0' was actually allocated from the
network named 'testnet', or that the bandwidth numbers were taken from
the portgroup 'admin'. However, if they are interested in that info,
they can always get the "inactive" XML for the domain.
An example of where this could cause problems is in virt-manager's
network device display, which shows the status of the device, but
allows you to edit that status info and save it as the new
config. Previously virt-manager would always display the information
in example [C] above, and allow editing that. With this patch, it will
instead display what is in [E] and allow editing it directly, which
could lead to some confusion. I would suggest that virt-manager have
an "edit" button which would change the display from the "live" xml to
the "inactive" xml, so that editing would be done on that; such a
change would both handle the new situation, and also be compatible
with older releases.
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>