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<div class="moz-cite-prefix">On 2014年01月16日 08:28, Ian Wells wrote:<br>
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<div dir="ltr">To clarify a couple of Robert's points, since we
had a conversation earlier:<br>
On 15 January 2014 23:47, Robert Li (baoli) <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:baoli@cisco.com"
target="_blank">baoli@cisco.com</a>></span> wrote:<br>
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--- do we agree that BDF address (or device id,
whatever you call it), and node id shouldn't be used as
attributes in defining a PCI flavor?
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<div>Note that the current spec doesn't actually exclude it
as an option. It's just an unwise thing to do. In
theory, you could elect to define your flavors using the
BDF attribute but determining 'the card in this slot is
equivalent to all the other cards in the same slot in
other machines' is probably not the best idea... We could
lock it out as an option or we could just assume that
administrators wouldn't be daft enough to try.<br>
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* the compute node needs to know the PCI flavor.
[...]
<div> - to support live migration, we
need to use it to create network xml</div>
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<div>I didn't understand this at first and it took me a
while to get what Robert meant here.<br>
<br>
This is based on Robert's current code for macvtap based
live migration. The issue is that if you wish to migrate
a VM and it's tied to a physical interface, you can't
guarantee that the same physical interface is going to be
used on the target machine, but at the same time you can't
change the libvirt.xml as it comes over with the migrating
machine. The answer is to define a network and refer out
to it from libvirt.xml. In Robert's current code he's
using the group name of the PCI devices to create a
network containing the list of equivalent devices (those
in the group) that can be macvtapped. Thus when the host
migrates it will find another, equivalent, interface.
This falls over in the use case under </div>
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but, with flavor we defined, the group could be a tag for this
purpose, and all Robert's design still work, so it ok, right?<br>
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<div>consideration where a device can be mapped using more
than one flavor, so we have to discard the use case or
rethink the implementation.<br>
<br>
There's a more complex solution - I think - where we
create a temporary network for each macvtap interface a
machine's going to use, with a name based on the instance
UUID and port number, and containing the device to map.
Before starting the migration we would create a
replacement network containing only the new device on the
target host; migration would find the network from the
name in the libvirt.xml, and the content of that network
would behave identically. We'd be creating libvirt
networks on the fly and a lot more of them, and we'd need
decent cleanup code too ('when freeing a PCI device,
delete any network it's a member of'), so it all becomes a
lot more hairy.<br>
-- <br>
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<div>Ian.<br>
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