Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends

[Antonios Motakis]

Hello,


On Wed, Jan 15, 2014 at 11:05 AM, Michael S. Tsirkin <address@hidden> wrote:
>
> On Mon, Jan 13, 2014 at 03:25:11PM +0100, Antonios Motakis wrote:
> > 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 change -mem-path to QemuOpts and add prealloc, share and unlink as 
> > properties
> > to it. HugeTLBFS requirements of -mem-path are relaxed, so any valid path 
> > can
> > be used now. The new properties allow more fine grained control over the 
> > guest
> > RAM backing store.
> >
> > 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-path /hugetlbfs,prealloc=on,share=on \
> >      -netdev type=vhost-user,id=net0,path=/path/to/sock,poll_time=2500 \
> >      -device virtio-net-pci,netdev=net0
>
> One other thing: it doesn't look like QMP/HMP commands
> to support this were added.
> Please add them so people can use it with hot-plugged virtio net.
>

It seems we are already able to use this via HMP. Vhost-user is
already mentioned in QAPI, and after booting a guest we can manually
add the network via monitor commands as such:

   netdev_add id=net0,type=vhost-user,path=/path/to/socket
   device_add driver=virtio-net-pci,netdev=net0

Is there something else expected in addition?

> > Changes from v5:
> >  - Split -mem-path unlink option to a separate patch
> >  - Fds are passed only in the ancillary data
> >  - Stricter message size checks on receive/send
> >  - Netdev vhost-user now includes path and poll_time options
> >  - The connection probing interval is configurable
> >
> > Changes from v4:
> >  - Use error_report for errors
> >  - VhostUserMsg has new field `size` indicating the following payload 
> > length.
> >    Field `flags` now has version and reply bits. The structure is packed.
> >  - Send data is of variable length (`size` field in message)
> >  - Receive in 2 steps, header and payload
> >  - Add new message type VHOST_USER_ECHO, to check connection status
> >
> > Changes from v3:
> >  - Convert -mem-path to QemuOpts with prealloc, share and unlink properties
> >  - Set 1 sec timeout when read/write to the unix domain socket
> >  - Fix file descriptor leak
> >
> > Changes from v2:
> >  - Reconnect when the backend disappears
> >
> > Changes from v1:
> >  - Implementation of vhost-user netdev backend
> >  - Code improvements
> >
> > Antonios Motakis (8):
> >   Convert -mem-path to QemuOpts and add prealloc and share properties
> >   New -mem-path option - unlink.
> >   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
> >   Add vhost-user reconnection
> >
> >  exec.c                            |  57 +++-
> >  hmp-commands.hx                   |   4 +-
> >  hw/net/vhost_net.c                | 144 +++++++---
> >  hw/net/virtio-net.c               |  42 ++-
> >  hw/scsi/vhost-scsi.c              |  13 +-
> >  hw/virtio/Makefile.objs           |   2 +-
> >  hw/virtio/vhost-backend.c         | 556 
> > ++++++++++++++++++++++++++++++++++++++
> >  hw/virtio/vhost.c                 |  46 ++--
> >  include/exec/cpu-all.h            |   3 -
> >  include/hw/virtio/vhost-backend.h |  40 +++
> >  include/hw/virtio/vhost.h         |   4 +-
> >  include/net/vhost-user.h          |  17 ++
> >  include/net/vhost_net.h           |  15 +-
> >  net/Makefile.objs                 |   2 +-
> >  net/clients.h                     |   3 +
> >  net/hub.c                         |   1 +
> >  net/net.c                         |   2 +
> >  net/tap.c                         |  16 +-
> >  net/vhost-user.c                  | 177 ++++++++++++
> >  qapi-schema.json                  |  21 +-
> >  qemu-options.hx                   |  24 +-
> >  vl.c                              |  41 ++-
> >  22 files changed, 1106 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
> >
> > --
> > 1.8.3.2
> >