On Wed, Oct 04, 2023 at 02:58:56PM +0200, Hanna Czenczek wrote:
> RFC:
> https://lists.nongnu.org/archive/html/qemu-devel/2023-03/msg04263.html
>
> v1:
> https://lists.nongnu.org/archive/html/qemu-devel/2023-04/msg01575.html
>
> v2:
> https://lists.nongnu.org/archive/html/qemu-devel/2023-07/msg02604.html
>
> v3:
> https://lists.nongnu.org/archive/html/qemu-devel/2023-09/msg03750.html
>
>
> Based-on: <20231004014532.1228637-1-stefanha@redhat.com>
> ([PATCH v2 0/3] vhost: clean up device reset)
>
>
> Hi,
>
> This v4 includes largely unchanged patches from v3. The main
> addition/change is what came out of the discussion between Stefan and me
> around how to proceed without SUSPEND/RESUME, which is that this series
> is now based on his reset fix, and it includes more documentation
> changes.
This looks good. I posted some minor comments on the new patches.
Stefan
>
> Changes in detail:
>
> - Patch 1: Fall-out from the reset fix: Currently, the status byte is
> effectively unused (qemu only uses it for resetting, which all
> back-ends ignore; DPDK uses it to announce potential feature
> negotiation failure, which qemu ignores). It is also not defined what
> exactly front-end or back-end should do with this byte, except
> pointing at the virtio spec, which however naturally does not say how
> this integrates with vhost-user’s RESET_DEVICE or [GS]ET_FEATURES.
> Furthermore, there does not seem to be a use for this; we have
> RESET_DEVICE for resetting, and we have [GS]ET_FEATURES (and
> REPLY_ACK, which can be used on SET_FEATURES) for feature
> negotation.
> Therefore, deprecate the status byte, pointing to those other commands
> instead.
>
> - Patch 2: Patch 4 defines a suspended state for the whole back-end if
> all vrings are stopped. I think this should be mentioned in
> GET_VRING_BASE, but upon trying to add it, I found that it does not
> even mention that it stops the vring (mentioned only in the Ring
> States section), and remembered that the whole description of both
> GET_VRING_BASE and SET_VRING_BASE really was not helpful when trying
> to implement a vhost-user back-end. Took the opportunity to overhaul
> both.
>
> - Patch 3: This one’s from v3, but quite heavily modified. Stefan
> suggested consistently defining the started/stopped and
> enabled/disabled states to be independent, and indeed doing so
> simplifies a whole lot of stuff. Specifically, it makes the magic
> “enabled/disabled when started” go away. Basically, I found this
> change alone is enough to remove the confusion I had with the existing
> documentation.
>
> - Patch 4: As suggested by Stefan, just define a suspended state without
> introducing SUSPEND. vDPA needs SUSPEND because its GET_VRING_BASE
> does not stop the vring, but vhost-user’s does, so we can define the
> suspended state to be when all vrings are stopped.
>
> - Patch 5: Reference the suspended state.
>
> - Patches 6 through 8: Unmodified, except for them being rebase on
> Stefan’s series.
>
>
> Hanna Czenczek (8):
> vhost-user.rst: Deprecate [GS]ET_STATUS
> vhost-user.rst: Improve [GS]ET_VRING_BASE doc
> vhost-user.rst: Clarify enabling/disabling vrings
> vhost-user.rst: Introduce suspended state
> vhost-user.rst: Migrating back-end-internal state
> vhost-user: Interface for migration state transfer
> vhost: Add high-level state save/load functions
> vhost-user-fs: Implement internal migration
>
> docs/interop/vhost-user.rst | 318 +++++++++++++++++++++++++++---
> include/hw/virtio/vhost-backend.h | 24 +++
> include/hw/virtio/vhost.h | 113 +++++++++++
> hw/virtio/vhost-user-fs.c | 101 +++++++++-
> hw/virtio/vhost-user.c | 148 ++++++++++++++
> hw/virtio/vhost.c | 241 ++++++++++++++++++++++
> 6 files changed, 917 insertions(+), 28 deletions(-)
>
> --
> 2.41.0
>