Re: [PATCH 0/6] vhost-user: Add suspend/resume

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Jul 11, 2023 at 05:52:22PM +0200, Hanna Czenczek wrote:
> Hi,
> 
> As discussed on the previous version of the virtio-fs migration series
> (https://lists.nongnu.org/archive/html/qemu-devel/2023-04/msg01575.html),
> we currently don’t have a good way to have a vhost-user back-end fully
> cease all operations, including background operations.  To work around
> this, we reset it, which is not an option for stateful devices like
> virtio-fs.
> 
> Instead, we want the same SUSPEND/RESUME model that vhost-vdpa already
> has, so that we can suspend back-ends when we want them to stop doing
> anything (i.e. on VM stop), and resume them later (i.e. on VM resume).
> This series adds these vhost-user operations to the protocol and
> implements them in qemu.  Furthermore, it has vhost-user and vhost-vdpa
> do roughly the same thing in their reset paths, as far as possible.
> That path will still remain as a fall-back if SUSPEND/RESUME is not
> implemented, and, given that qemu’s vhost-vdpa code currently does not
> make use of RESUME, it is actually always used for vhost-vdpa (to take
> the device out of a suspended state).
> 
> 
> Hanna Czenczek (6):
>   vhost-user.rst: Add suspend/resume
>   vhost-vdpa: Move vhost_vdpa_reset_status() up
>   vhost: Do not reset suspended devices on stop
>   vhost-user: Implement suspend/resume
>   vhost-vdpa: Match vhost-user's status reset
>   vhost-user: Have reset_status fall back to reset
> 
>  docs/interop/vhost-user.rst    |  35 +++++++++++-
>  include/hw/virtio/vhost-vdpa.h |   2 -
>  include/hw/virtio/vhost.h      |   8 +++
>  hw/virtio/vhost-user.c         | 101 ++++++++++++++++++++++++++++++++-
>  hw/virtio/vhost-vdpa.c         |  41 ++++++-------
>  hw/virtio/vhost.c              |   8 ++-
>  6 files changed, 169 insertions(+), 26 deletions(-)

Hi Hanna,
I posted comments but wanted to say great job! There was a long and
somewhat messy email discussion to figure out how to proceed and you
came up with a clean patch series that solves the issues.

Stefan

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