The virtio queue reset function has already been defined in the virtio spec 1.2.
The relevant virtio spec information is here:

    https://github.com/oasis-tcs/virtio-spec/issues/124
    https://github.com/oasis-tcs/virtio-spec/issues/139

This patch set is to support this function in QEMU. It consists of several parts:
1. Patches 1-7 are the basic interfaces for vq reset in virtio and virtio-pci.
2. Patches 8-11 support vq reset and vq restart for vhost-kernel.
3. Patches 12-14 support vq reset and vq restart for virtio-net.
5. Patch 15 enables the vq reset feature for vhost-kernel.

The process of virtqueue reset can be concluded as:
1. The virtqueue is disabled when VIRTIO_PCI_COMMON_Q_RESET is written.
2. Then the virtqueue can be optionally restarted(re-enabled).

Since this patch set involves multiple modules and seems a bit messy, we briefly describe the
calling process for different modes below.
virtio-net:
1. VIRTIO_PCI_COMMON_Q_RESET is written [virtio-pci]
    -> virtio_queue_reset() [virtio]
        -> virtio_net_queue_reset() [virtio-net]
        -> __virtio_queue_reset()
2. VIRTIO_PCI_COMMON_Q_ENABLE is written [virtio-pci]
    -> set enabled, reset status of vq.

vhost-kernel:
1. VIRTIO_PCI_COMMON_Q_RESET is written [virtio-pci]
    -> virtio_queue_reset() [virtio]
        -> virtio_net_queue_reset() [virtio-net]
            -> vhost_net_virtqueue_stop() [vhost-net]
                -> vhost_net_set_backend() [vhost]
                -> vhost_virtqueue_stop()
        -> __virtio_queue_reset()
2. VIRTIO_PCI_COMMON_Q_ENABLE is written [virtio-pci]
    -> virtio_queue_enable() [virtio]
        -> virtio_net_queue_enable() [virtio-net]
            -> vhost_net_virtqueue_restart() [vhost-net]
                -> vhost_virtqueue_start() [vhost]
                -> vhost_net_set_backend()
    -> set enabled, reset status of vq.


Test environment and method:
    Host: 5.19.0-rc3 (With vq reset support)
    Qemu: QEMU emulator version 7.0.50
    Guest: 5.19.0-rc3 (With vq reset support)
    Test Cmd: ethtool -g eth1; ethtool -G eth1 rx $1 tx $2; ethtool -g eth1;

    The drvier can resize the virtio queue, then virtio queue reset function should
    be triggered.

    The default is split mode, modify Qemu virtio-net to add PACKED feature to
    test packed mode.

Guest Kernel Patch:
    https://lore.kernel.org/bpf/20220801063902.129329-1-xuanzhuo@linux.alibaba.com/

Host Kernel Patch:
    https://lore.kernel.org/bpf/20220825085610.80315-1-kangjie.xu@linux.alibaba.com/

Looking forward to your review and comments. Thanks.

changelog:

v6:
  1. fix for compile fail for mingw 32 by adding funcs inside vhost_net-stub.c
  2. add one new commit to add vq reset support inside virtio-net (not wait for vhost-user)

v5:
  1. vhost_net_virtqueue_restart() use -EBUSY replace -ENOTSUP. @Jason
  2. reuse  VHOST_FILE_UNBIND. @Jason

v4:
  1. Add explanation for preventing userspace datapath in virtio-net.
  2. Return error when vhost is not started in vhost_net_virtqueue_restart().
  3. Reset the virtqueue in the device reusing vhost_virtqueue_stop().
  4. Disable queue reset feature for pre-7.2 machine.

v3:
  1. Remove support for vhost-user in this series and refactor the code.
  2. Rename 'vhost_net_virtqueue_stop' to 'vhost_net_virtqueue_reset'.
  3. Make PCI transport ready before device ready when queue_enabled is set to true.
  4. Add some comments.

v2:
  1. Add support for vhost-net kernel scenario.
  2. Add a new vhost-user message VHOST_USER_RESET_VRING.
  3. Add migration compatibility for virtqueue reset.

Kangjie Xu (10):
  virtio: introduce virtio_queue_enable()
  virtio: core: vq reset feature negotation support
  virtio-pci: support queue enable
  vhost: expose vhost_virtqueue_start()
  vhost: expose vhost_virtqueue_stop()
  vhost-net: vhost-kernel: introduce vhost_net_virtqueue_reset()
  vhost-net: vhost-kernel: introduce vhost_net_virtqueue_restart()
  virtio-net: introduce flush_or_purge_queued_packets()
  virtio-net: support queue_enable
  vhost: vhost-kernel: enable vq reset feature

Xuan Zhuo (5):
  virtio: introduce __virtio_queue_reset()
  virtio: introduce virtio_queue_reset()
  virtio-pci: support queue reset
  virtio-net: support queue reset
  virtio-net: enable vq reset feature

 hw/core/machine.c              |  4 +-
 hw/net/vhost_net-stub.c        | 12 ++++++
 hw/net/vhost_net.c             | 79 ++++++++++++++++++++++++++++++++++
 hw/net/virtio-net.c            | 57 +++++++++++++++++++++---
 hw/virtio/vhost.c              | 16 +++----
 hw/virtio/virtio-pci.c         | 16 +++++++
 hw/virtio/virtio.c             | 62 +++++++++++++++++++-------
 include/hw/virtio/vhost.h      |  5 +++
 include/hw/virtio/virtio-pci.h |  5 +++
 include/hw/virtio/virtio.h     |  8 +++-
 include/net/vhost_net.h        |  4 ++
 11 files changed, 236 insertions(+), 32 deletions(-)

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2.32.0.3.g01195cf9f