Re: [Qemu-devel] [PATCH v10 00/18] Vhost and vhost-net support for userspace based backends

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

On Tue, May 27, 2014 at 03:03:21PM +0300, Nikolay Nikolaev 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 realized by 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
> domain socket backend. Vhost-user is client/server agnostic regarding the
> chardev, however it does not support the 'nowait' and 'telnet' options.
> 
> We rely on the memdev with a memory-file backend. The backend's share=on option
> should be used. 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 a new netdev backend
> that is intended to initialize vhost-net with vhost-user backend.
> 
> Example usage:
> 
> qemu -m 512 \
>      -object memory-file,id=mem,size=512M,mem-path=/hugetlbfs,share=on \
>      -numa node,memdev=mem \
>      -chardev socket,id=chr0,path=/path/to/socket \
>      -netdev type=vhost-user,id=net0,chardev=chr0 \
>      -device virtio-net-pci,netdev=net0
> 
> On non-MSIX guests the vhost feature can be forced using a special option:
> 
> ...
>      -netdev type=vhost-user,id=net0,chardev=chr0,vhostforce
> ...
> 
> In order to use ioeventfds, kvm should be enabled.
> 
> The work is made on top of the NUMA patch series v3.2
> http://lists.gnu.org/archive/html/qemu-devel/2014-05/msg02706.html
> 
> This code can be pulled from git@github.com:virtualopensystems/qemu.git vhost-user-v10
> A simple functional test is available in tests/vhost-user-test.c
> 
> A reference vhost-user slave for testing is also available from git@github.com:virtualopensystems/vapp.git
> 
> Changes from v9:
>  - Rebased on the NUMA memdev patchseries and reworked to use memdev

OK so I should wait until NUMA memdev is merged
before merging this one?

>  - Removed -mem-path refactoring
>  - Removed all reconnection code
>  - Fixed 100% CPU usage in the G_IO_HUP handler after disconnect
>  - Reworked vhost feature bits handling so vhost-user has better control in the negotiation
> 
> Changes from v8:
>  - Removed prealloc property from the -mem-path refactoring
>  - Added and use new function - kvm_eventfds_enabled
>  - Add virtio_queue_get_avail_idx used in vhost_virtqueue_stop to
>    get a sane value in case of VHOST_GET_VRING_BASE failure
>  - vhost user uses kvm_eventfds_enabled to check whether the ioeventfd
>    capability of KVM is available
>  - Added flag VHOST_USER_VRING_NOFD_MASK to be set when KICK, CALL or ERR file
>    descriptor is invalid or ioeventfd is not available
> 
> Changes from v7:
>  - Slave reconnection when using chardev in server mode
>  - qtest vhost-user-test added
>  - New qemu_chr_fe_get_msgfds for reading multiple fds from the chardev
>  - Mandatory features in vhost_dev, used on reconnect to verify for conflicts
>  - Add vhostforce parameter to -netdev vhost-user (for non-MSIX guests)
>  - Extend libqemustub.a to support qemu-char.c
> 
> 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
> 
> 
> ---
> 
> Nikolay Nikolaev (18):
>       Add kvm_eventfds_enabled function
>       Add chardev API qemu_chr_fe_read_all
>       Add chardev API qemu_chr_fe_set_msgfds
>       Add chardev API qemu_chr_fe_get_msgfds
>       Add G_IO_HUP handler for socket chardev
>       vhost: add vhost_get_features and vhost_ack_features
>       vhost_net should call the poll callback only when it is set
>       Refactor virtio-net to use generic get_vhost_net
>       vhost_net_init will use VhostNetOptions to get all its arguments
>       Add vhost_ops to vhost_dev struct and replace all relevant ioctls
>       Add vhost-backend and VhostBackendType
>       Add vhost-user as a vhost backend.
>       vhost-net: vhost-user feature bits support
>       Add new vhost-user netdev backend
>       Add the vhost-user netdev backend to the command line
>       Add vhost-user protocol documentation
>       libqemustub: add stubs to be able to use qemu-char.c
>       Add qtest for vhost-user
> 
> 
>  docs/specs/vhost-user.txt         |  261 ++++++++++++++++++++++++++++
>  hmp-commands.hx                   |    4 
>  hw/net/vhost_net.c                |  228 +++++++++++++++++--------
>  hw/net/virtio-net.c               |   29 +--
>  hw/scsi/vhost-scsi.c              |   45 +++--
>  hw/virtio/Makefile.objs           |    2 
>  hw/virtio/vhost-backend.c         |   71 ++++++++
>  hw/virtio/vhost-user.c            |  342 +++++++++++++++++++++++++++++++++++++
>  hw/virtio/vhost.c                 |   82 ++++++---
>  include/hw/virtio/vhost-backend.h |   38 ++++
>  include/hw/virtio/vhost.h         |   13 +
>  include/net/vhost-user.h          |   17 ++
>  include/net/vhost_net.h           |   11 +
>  include/sysemu/char.h             |   44 +++++
>  include/sysemu/kvm.h              |   11 +
>  kvm-all.c                         |    4 
>  kvm-stub.c                        |    1 
>  net/Makefile.objs                 |    2 
>  net/clients.h                     |    3 
>  net/hub.c                         |    1 
>  net/net.c                         |   25 ++-
>  net/tap.c                         |   18 ++
>  net/vhost-user.c                  |  265 +++++++++++++++++++++++++++++
>  qapi-schema.json                  |   19 ++
>  qemu-char.c                       |  277 +++++++++++++++++++++++++++---
>  qemu-options.hx                   |   18 ++
>  stubs/Makefile.objs               |    8 +
>  stubs/bdrv-commit-all.c           |    7 +
>  stubs/chr-msmouse.c               |    7 +
>  stubs/get-next-serial.c           |    3 
>  stubs/is-daemonized.c             |    7 +
>  stubs/machine-init-done.c         |    6 +
>  stubs/monitor-init.c              |    6 +
>  stubs/notify-event.c              |    6 +
>  stubs/vc-init.c                   |    7 +
>  tests/Makefile                    |    4 
>  tests/vhost-user-test.c           |  312 ++++++++++++++++++++++++++++++++++
>  37 files changed, 2011 insertions(+), 193 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
>  create mode 100644 stubs/bdrv-commit-all.c
>  create mode 100644 stubs/chr-msmouse.c
>  create mode 100644 stubs/get-next-serial.c
>  create mode 100644 stubs/is-daemonized.c
>  create mode 100644 stubs/machine-init-done.c
>  create mode 100644 stubs/monitor-init.c
>  create mode 100644 stubs/notify-event.c
>  create mode 100644 stubs/vc-init.c
>  create mode 100644 tests/vhost-user-test.c
> 
> --
> Signature