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

[Antonios Motakis]

On Wed, Jan 15, 2014 at 10:07 AM, Michael S. Tsirkin <address@hidden> wrote:
> On Tue, Jan 14, 2014 at 07:13:43PM +0100, Antonios Motakis wrote:
>>
>>
>>
>> On Tue, Jan 14, 2014 at 12:33 PM, 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.
>>
>>     Some meta comments.
>>
>>     Something that makes this patch harder to review is how it's
>>     split up. Generally IMHO it's not a good idea to repeatedly
>>     edit same part of file adding stuff in patch after patch,
>>     it's only making things harder to read if you add stubs, then fill them 
>> up.
>>     (we do this sometimes when we are changing existing code, but
>>     it is generally not needed when adding new code)
>>
>>     Instead, split it like this:
>>
>>     1. general refactoring, split out linux specific and generic parts
>>        and add the ops indirection
>>     2. add new files for vhost-user with complete implementation.
>>        without command line to support it, there will be no way to use it,
>>        but should build fine.
>>     3. tie it all up with option parsing
>>
>>
>>     Generic vhost and vhost net files should be kept separate.
>>     Don't let vhost net stuff seep back into generic files,
>>     we have vhost-scsi too.
>>     I would also prefer that userspace vhost has its own files.
>>
>>
>> Ok, we'll keep this into account.
>>
>>
>>
>>     We need a small test server qemu can talk to, to verify things
>>     actually work.
>>
>>
>> We have implemented such a test app: 
>> https://github.com/virtualopensystems/vapp
>>
>> We use it for testing, and also as a reference implementation. A client is 
>> also
>> included.
>>
>
> Sounds good. Can we include this in qemu and tie
> it into the qtest framework?
> From a brief look, it merely needs to be tweaked for portability,
> unless

Could you provide some hints/examples about what it would look like to
use qtest and pxe ROM? We have looked but haven't found anything
obvious.

Thanks
Antonios

>
>>
>>     Already commented on: reuse the chardev syntax and preferably code.
>>     We already support a bunch of options there for
>>     domain sockets that will be useful here, they should
>>     work here as well.
>>
>>
>> We adapted the syntax for this to be consistent with chardev. What we didn't
>> use, it is not obvious at all to us on how they should be used; a lot of the
>> chardev options just don't apply to us.
>>
>
> Well server option should work at least.
> nowait can work too?
>
> Also, if reconnect is useful it should be for chardevs too, so if we don't
> share code, need to code it in two places to stay consistent.
>
> Overall sharing some code might be better ...
>
>>     In particular you shouldn't require filesystem access by qemu,
>>     passing fd for domain socket should work.
>>
>>
>> We can add an option to pass an fd for the domain socket if needed. However 
>> as
>> far as we understand, chardev doesn't do that either (at least form looking 
>> at
>> the man page). Maybe we misunderstand what you mean.
>
> Sorry. I got confused with e.g. tap which has this. This might be
> useful but does not have to block this patch.
>
>>
>>
>>     > 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
>>
>>     It's not clear which parts of -mem-path are required for vhost-user.
>>     It should be documented somewhere, made clear in -help
>>     and should fail gracefully if misconfigured.
>>
>>
>>
>> Ok.
>>
>>
>>
>>     >
>>     > 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
>>     >
>>
>>