Re: [Qemu-devel] [PATCH v7 00/13] Vhost and vhost-net support for userspace based backends

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jan 31, 2014 at 06:34:29PM +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. For this communication we use a chardev with a unix socket
> backend. Vhost-user is client/server agnostic regarding the chardev, however
> it does not support the 'nowait' and 'telnet' options.
> 
> We change -mem-path to QemuOpts and add prealloc and share as properties
> to it. HugeTLBFS is required for this option to work.
> 
> 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.


You mentioned that there will be an in-tree utility that can
communicate over this channel from the other side.
Did I miss it in this patchset or is it not included yet?

> Example usage:
> 
> qemu -m 1024 -mem-path /hugetlbfs,share=on \
>      -chardev socket,id=chr0,path=/path/to/socket \
>      -netdev type=vhost-user,id=net0,chardev=chr0 \
>      -device virtio-net-pci,netdev=net0
> 
> This code can be pulled from git@github.com:virtualopensystems/qemu.git vhost-user-v7
> 
> A reference vhost-user slave for testing is available from git@github.com:virtualopensystems/vapp.git
> 
> TODOs include:
>  - Include a test in QEMU to avoid regressions
>  - Slave reconnection and nowait support
> 
> Changes from v6:
>  - Remove the 'unlink' property of '-mem-path'
>  - Extend qemu-char: blocking read, send fds, monitor for connection close
>  - Vhost-user uses chardev as a backend
>  - Poll and reconnect removed (no VHOST_USER_ECHO).
>  - Disconnect is deteced by the chardev (G_IO_HUP event)
>  - vhost-backend.c split to vhost-user.c
> 
> 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 (13):
>   Convert -mem-path to QemuOpts and add prealloc and share properties
>   Add chardev API  qemu_chr_fe_read_all
>   Add chardev API qemu_chr_fe_set_msgfds
>   Add G_IO_HUP handler for socket chardev
>   vhost_net should call the poll callback only when it is set
>   Refactor virtio-net to use a generic get_vhost_net
>   vhost_net_init will use VhostNetOptions to get all its arguments
>   Add vhost_ops to the vhost_dev struct and replace all relevant ioctls
>   Add vhost-backend and VhostBackendType
>   Add vhost-user as a vhost backend.
>   Add new vhost-user netdev backend
>   Add the vhost-user netdev backend to command line
>   Add vhost-user protocol documentation
> 
>  docs/specs/vhost-user.txt         | 249 ++++++++++++++++++++++++++++
>  exec.c                            |  30 +++-
>  hmp-commands.hx                   |   4 +-
>  hw/net/vhost_net.c                | 142 +++++++++++-----
>  hw/net/virtio-net.c               |  42 ++---
>  hw/scsi/vhost-scsi.c              |  20 ++-
>  hw/virtio/Makefile.objs           |   2 +-
>  hw/virtio/vhost-backend.c         |  71 ++++++++
>  hw/virtio/vhost-user.c            | 331 ++++++++++++++++++++++++++++++++++++++
>  hw/virtio/vhost.c                 |  55 ++++---
>  include/exec/cpu-all.h            |   3 -
>  include/hw/virtio/vhost-backend.h |  38 +++++
>  include/hw/virtio/vhost.h         |   8 +-
>  include/net/vhost-user.h          |  17 ++
>  include/net/vhost_net.h           |  11 +-
>  include/sysemu/char.h             |  28 ++++
>  net/Makefile.objs                 |   2 +-
>  net/clients.h                     |   3 +
>  net/hub.c                         |   1 +
>  net/net.c                         |   2 +
>  net/tap.c                         |  18 ++-
>  net/vhost-user.c                  | 217 +++++++++++++++++++++++++
>  qapi-schema.json                  |  18 ++-
>  qemu-char.c                       | 185 ++++++++++++++++++++-
>  qemu-options.hx                   |  25 ++-
>  vl.c                              |  37 ++++-
>  26 files changed, 1425 insertions(+), 134 deletions(-)
>  create mode 100644 docs/specs/vhost-user.txt
>  create mode 100644 hw/virtio/vhost-backend.c
>  create mode 100644 hw/virtio/vhost-user.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
>