[Qemu-devel] [PATCHv2 0/6] Vhost and vhost-net support for userspace based backends

[Antonios Motakis]

In this patch series we would like to introduce our approach for putting a
virtio-net backend in an external userspace process. Our eventual target is to
run the network backend in the Snabbswitch ethernet switch, while receiving
traffic from a guest inside QEMU/KVM which runs an unmodified virtio-net
implementation.

For this, we are working into extending vhost to allow equivalent functionality
for userspace. Vhost already passes control of the data plane of virtio-net to
the host kernel; we want to realize a similar model, but for userspace.

In this patch series the concept of a vhost-backend is introduced.

We define two vhost backend types - vhost-kernel and vhost-user. The former is
the interface to the current kernel module implementation. Its control plane is
ioctl based. The data plane is the kernel directly accessing the QEMU allocated,
guest memory.

In the new vhost-user backend, the control plane is based on communication
between QEMU and another userspace process using a unix domain socket. This
allows to implement a virtio backend for a guest running in QEMU, inside the
other userspace process.

We introduce a new memory related flag: -mem-share. When used the ram is
created as a shared memory object. When combined with -mem-path, it will reuse
a HugeTLBFS file instead of /dev/shm. This flag also implies -mem-prealloc.

The data path is realized by directly accessing the vrings and the buffer data
off the guest's memory.

The current user of vhost-user is only vhost-net. We add new netdev backend
that is intended to initialize vhost-net with vhost-user backend.

Example usage:

qemu -m 1024 -mem-share -mem-path /hugetlbfs \
     -netdev type=vhost-user,id=net0,file=/path/to/sock \
     -device virtio-net-pci,netdev=net0

To do:
 - No migration, (probably) no ram hotplug
 - Will not start if the socket is not available
 - No reconnect when the backend disappears

Changes from v1:
 - Implementation of vhost-user netdev backend
 - Code improvements

Antonios Motakis (6):
  Add -mem-share option
  Decouple vhost from kernel interface
  Add vhost-user skeleton
  Add domain socket communication for vhost-user backend
  Add vhost-user calls implementation
  Add new vhost-user netdev backend

 exec.c                            |  71 +++++---
 hw/net/vhost_net.c                | 127 +++++++++-----
 hw/net/virtio-net.c               |  42 ++---
 hw/scsi/vhost-scsi.c              |  12 +-
 hw/virtio/Makefile.objs           |   2 +-
 hw/virtio/vhost-backend.c         | 351 ++++++++++++++++++++++++++++++++++++++
 hw/virtio/vhost.c                 |  46 ++---
 include/exec/cpu-all.h            |   1 +
 include/hw/virtio/vhost-backend.h |  37 ++++
 include/hw/virtio/vhost.h         |   4 +-
 include/net/vhost-user.h          |  17 ++
 include/net/vhost_net.h           |  14 +-
 net/Makefile.objs                 |   2 +-
 net/clients.h                     |   3 +
 net/hub.c                         |   1 +
 net/net.c                         |   2 +
 net/tap.c                         |  16 +-
 net/vhost-user.c                  |  95 +++++++++++
 qapi-schema.json                  |  18 +-
 qemu-options.hx                   |   9 +
 vl.c                              |   5 +
 21 files changed, 751 insertions(+), 124 deletions(-)
 create mode 100644 hw/virtio/vhost-backend.c
 create mode 100644 include/hw/virtio/vhost-backend.h
 create mode 100644 include/net/vhost-user.h
 create mode 100644 net/vhost-user.c

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1.8.3.2