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Re: [Qemu-devel] [PATCH RFC 00/14] vhost-user: shutdown and reconnection
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH RFC 00/14] vhost-user: shutdown and reconnection |
Date: |
Thu, 26 Nov 2015 12:33:22 +0200 |
On Wed, Sep 09, 2015 at 01:09:52AM +0200, address@hidden wrote:
> From: Marc-André Lureau <address@hidden>
>
> In a previous series "Add feature to start QEMU without vhost-user
> backend", Tetsuya Mukawa proposed to allow the vhost-user backend to
> disconnect and reconnect. However, Michael Tsirkin pointed out that
> you can't do that without extra care, because the guest and hypervisor
> don't know the slave ring manipulation state, there might be pending
> replies for example that could be lost, and suggested to reset the
> guest queues, but this requires kernel changes, and it may have to
> clear the ring and lose queued packets.
>
> The following series starts from the idea that the slave can request a
> "managed" shutdown instead and later recover (I guess the use case for
> this is to allow for example to update static dispatching/filter rules
> etc)
I'm still not sure users actually need this. I am inclined to think we
should teach guests to respond to NEED_RESET status. Then to handle
disconnect, we would
- deactivate the disconnected backend
- stop VM, and wait for a reconnect
- set NEED_RESET status, and re-activate the backend
after guest reset
--
MST
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