Re: [PATCH v1 00/13] various virtio docs, fixes and tweaks

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

On Tue, Mar 22, 2022 at 03:50:28PM +0000, Alex Bennée wrote:
> 
> "Michael S. Tsirkin" <mst@redhat.com> writes:
> 
> > On Mon, Mar 21, 2022 at 03:30:24PM +0000, Alex Bennée wrote:
> >> Hi,
> >> 
> >> This series is a sub-set of patches while I was trying to re-rev my
> >> virtio-rpmb patches. It attempts to address a few things:
> >> 
> >>   - improve documentation for virtio/vhost/vhost-user
> >>   - document some of the API
> >>   - a hacky fix for F_CONFIG handling
> >>   - putting VhostUserState on a diet, make VhostUserHostNotifier dynamic
> >
> > So I think this is best deferred until after the release,
> > more of a cleanup than a bugfix.
> 
> Sorry I should have made it clearer - I wasn't intending this for 7.0
> but I also didn't want it bound up with the rpmb changes which will take
> longer to land.

Makes sense, I was just making sure.

> >
> > I will tag this series, but please do remind me after the release
> > to help make sure it does not get lost.
> >
> >
> >> In particular I've been trying to better understand how vhost-user
> >> interactions are meant to work and why there are two different methods
> >> for instantiating them. If my supposition is correct perhaps a number
> >> of devices that don't have in-kernel vhost equivalents could be converted?
> >
> > Hope I understand your question.  Well we started off with saying
> > vhost-user is just a backend, so should not affect the frontend device.
> > This is clean and makes migration work e.g. you can migrate between
> > different backends, but it makes adding features more work.
> 
> This is covered in the doc patch, specifically:
> 
>   vhost_ops vs TYPE_VHOST_USER_BACKEND

I guess I misunderstood then - what was the question again?

> >> hard to trigger the code. Is this rarely used code or just requires
> >> backends we don't see in the testing?
> >
> > Which function are you asking about exactly?
> 
>   vhost_user_slave_handle_vring_host_notifier
> 
> which is the only place where a mapping is set up AFAICT.

Well it's mostly for use with vdpa, but I think vhost user bridge
is supposed to support that with a special flag (-H use host notifier).
It's for debugging purposes as it wastes lots of CPU polling
the notification memory.

> >
> >> Alex Bennée (10):
> >>   hw/virtio: move virtio-pci.h into shared include space
> >>   virtio-pci: add notification trace points
> >>   hw/virtio: add vhost_user_[read|write] trace points
> >>   vhost-user.rst: add clarifying language about protocol negotiation
> >>   libvhost-user: expose vu_request_to_string
> >>   docs/devel: start documenting writing VirtIO devices
> >>   include/hw: start documenting the vhost API
> >>   contrib/vhost-user-blk: fix 32 bit build and enable
> >>   hw/virtio/vhost-user: don't suppress F_CONFIG when supported
> >>   virtio/vhost-user: dynamically assign VhostUserHostNotifiers
> >> 
> >> Paolo Bonzini (3):
> >>   docs: vhost-user: clean up request/reply description
> >>   docs: vhost-user: rewrite section on ring state machine
> >>   docs: vhost-user: replace master/slave with front-end/back-end
> >> 
> >>  docs/devel/index-internals.rst            |   1 +
> >>  docs/devel/virtio-backends.rst            | 214 +++++++++
> >>  docs/interop/vhost-user-gpu.rst           |  10 +-
> >>  docs/interop/vhost-user.rst               | 555 ++++++++++++----------
> >>  meson.build                               |   2 +-
> >>  include/hw/virtio/vhost-user.h            |  43 +-
> >>  include/hw/virtio/vhost.h                 | 132 ++++-
> >>  {hw => include/hw}/virtio/virtio-pci.h    |   0
> >>  subprojects/libvhost-user/libvhost-user.h |   9 +
> >>  contrib/vhost-user-blk/vhost-user-blk.c   |   6 +-
> >>  hw/scsi/vhost-user-scsi.c                 |   1 +
> >>  hw/virtio/vhost-scsi-pci.c                |   2 +-
> >>  hw/virtio/vhost-user-blk-pci.c            |   2 +-
> >>  hw/virtio/vhost-user-fs-pci.c             |   2 +-
> >>  hw/virtio/vhost-user-i2c-pci.c            |   2 +-
> >>  hw/virtio/vhost-user-input-pci.c          |   2 +-
> >>  hw/virtio/vhost-user-rng-pci.c            |   2 +-
> >>  hw/virtio/vhost-user-scsi-pci.c           |   2 +-
> >>  hw/virtio/vhost-user-vsock-pci.c          |   2 +-
> >>  hw/virtio/vhost-user.c                    | 133 ++++--
> >>  hw/virtio/vhost-vsock-pci.c               |   2 +-
> >>  hw/virtio/virtio-9p-pci.c                 |   2 +-
> >>  hw/virtio/virtio-balloon-pci.c            |   2 +-
> >>  hw/virtio/virtio-blk-pci.c                |   2 +-
> >>  hw/virtio/virtio-input-host-pci.c         |   2 +-
> >>  hw/virtio/virtio-input-pci.c              |   2 +-
> >>  hw/virtio/virtio-iommu-pci.c              |   2 +-
> >>  hw/virtio/virtio-net-pci.c                |   2 +-
> >>  hw/virtio/virtio-pci.c                    |   5 +-
> >>  hw/virtio/virtio-rng-pci.c                |   2 +-
> >>  hw/virtio/virtio-scsi-pci.c               |   2 +-
> >>  hw/virtio/virtio-serial-pci.c             |   2 +-
> >>  subprojects/libvhost-user/libvhost-user.c |   2 +-
> >>  contrib/vhost-user-blk/meson.build        |   3 +-
> >>  hw/virtio/trace-events                    |  10 +-
> >>  35 files changed, 831 insertions(+), 333 deletions(-)
> >>  create mode 100644 docs/devel/virtio-backends.rst
> >>  rename {hw => include/hw}/virtio/virtio-pci.h (100%)
> >> 
> >> -- 
> >> 2.30.2
> 
> 
> -- 
> Alex Bennée