Re: [Qemu-devel] [RFC PATCH 0/2] implement the failover feature for assigned network devices

[Markus Armbruster <armbru@redhat.com>]

Jens Freimann <jfreimann@redhat.com> writes:

> On Fri, Apr 05, 2019 at 09:56:29AM +0100, Dr. David Alan Gilbert wrote:
>>* Jens Freimann (jfreimann@redhat.com) wrote:
> [...]
>>> > Commandline: There is a dependency between vfio-pci and virtio-net
>>> > devices. One points to the other via new parameters
>>> > primar=<primary qdev id> and standby='<standby qdev id>'. This means
>>> > that the primary device needs to be specified after standby device on
>>> > the qemu command line. Not sure how to solve this.
>>> >
>>> > Error handling: Patches don't cover all possible error scenarios yet.
>>> >
>>> > I have tested this with a mlx5 NIC and was able to migrate the VM with
>>> > above mentioned workarounds for open problems.
>>> >
>>> > Command line example:
>>> >
>>> > qemu-system-x86_64 -enable-kvm -m 3072 -smp 3 \
>>> >        -machine q35,kernel-irqchip=split -cpu host   \
>>> >        -k fr   \
>>> >        -serial stdio   \
>>> >        -net none \
>>> >        -qmp unix:/tmp/qmp.socket,server,nowait \
>>> >        -monitor telnet:127.0.0.1:5555,server,nowait \
>>> >        -device pcie-root-port,id=root0,multifunction=on,chassis=0,addr=0xa \
>>> >        -device pcie-root-port,id=root1,bus=pcie.0,chassis=1 \
>>> >        -device pcie-root-port,id=root2,bus=pcie.0,chassis=2 \
>>> >        -netdev tap,script=/root/bin/bridge.sh,downscript=no,id=hostnet1,vhost=on \
>>> >        -device virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:6f:55:cc,bus=root2,primary=hostdev0 \
>>> >        -device vfio-pci,host=5e:00.2,id=hostdev0,bus=root1,standby=net1 \
>>
>>Yes, that's a bit grim; it's circular dependency on the 'hostdev0' and
>>'net1' id's.  cc'ing in Markus.
>
> Dan had an idea how to avoid having to specify the id for the
> virtio-net device. I'm currently looking into it, but it seems like it
> should work. 

Excellent.  A circular dependency between -device could only lead to
trouble.