[RFC 0/1] virtio-net: add support for SR-IOV emulation

[Yui Washizu <yui.washidu@gmail.com>]

This patch series is the first step towards enabling
hardware offloading of the L2 packet switching feature on virtio-net device to host machine.
We are considering that this hardware offloading enables
the use of high-performance networks in virtual infrastructures,
such as container infrastructures on VMs.

To enable L2 packet switching by SR-IOV VFs, we are considering the following:
- making the guest recognize virtio-net devices as SR-IOV PF devices
  (archived with this patch series)
- allowing virtio-net devices to connect SR-IOV VFs to the backend networks,
  leaving the L2 packet switching feature to the management layer like libvirt
  - This makes hardware offloading of L2 packet switching possible.
    For example, when using vDPA devices, it allows the guest
    to utilize SR-IOV NIC embedded switch of hosts.

This patch series aims to enable SR-IOV emulation on virtio-net devices.
With this series, the guest can identify the virtio-net device as an SR-IOV PF device.
The newly added property 'sriov_max_vfs' allows us to enable the SR-IOV feature
on the virtio-net device.
Currently, we are unable to specify the properties of a VF created from the guest.
The properties are set to their default values.
In the future, we plan to allow users to set the properties.

qemu-system-x86_64 --device virtio-net,sriov_max_vfs=<num>
# when 'sriov_max_vfs' is present, the SR-IOV feature will be automatically enabled
# <num> means the max number of VF on guest

Example commands to create VFs in virtio-net device from the guest:

guest% readlink -f /sys/class/net/eth1/device
 /sys/devices/pci0000:00/0000:00:02.0/0000:01:00.0/virtio1
guest% echo "2" > /sys/devices/pci0000:00/0000:00:02.0/0000:01:00.0/sriov_numvfs
guest% ip link show
 eth0: ....
 eth1: ....
 eth2: .... #virtual VF created
 eth3: .... #virtual VF created
 
Please note that communication between VF and PF/VF is not possible by this patch series itself.

Yui Washizu (1):
  virtio-pci: add SR-IOV capability

 hw/pci/msix.c                  |  8 +++--
 hw/pci/pci.c                   |  4 +++
 hw/virtio/virtio-pci.c         | 62 ++++++++++++++++++++++++++++++----
 include/hw/virtio/virtio-pci.h |  1 +
 4 files changed, 66 insertions(+), 9 deletions(-)

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2.39.3