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Re: [Qemu-devel] [PATCH v4 for-4.0 0/7] vhost-user-blk: Add support for

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH v4 for-4.0 0/7] vhost-user-blk: Add support for backend reconnecting
Date: Fri, 11 Jan 2019 12:24:00 -0500

On Fri, Jan 11, 2019 at 03:53:42PM +0000, Stefan Hajnoczi wrote:
> I'm concerned that this approach to device recovery is invasive and hard
> to test.  Instead I would use VIRTIO's Device Status Field
> DEVICE_NEEDS_RESET bit to tell the guest driver that a reset is
> necessary.  This is more disruptive - drivers either have to resubmit or
> fail I/O with EIO - but it's also simple and more likely to work
> correctly (it only needs to be implemented correctly in the guest
> driver, not in the many available vhost-user backend implementations).
> Stefan

Unfortunately drivers don't support DEVICE_NEEDS_RESET yet.
I'll be happy to accept patches, but this means we
can't depend on DEVICE_NEEDS_RESET for basic functionality
like reconnect. And given virtio 1.0 has been there
for a while now, I suspect the only way to start using
it is by adding a new feature flag.

Unfortunate but true.


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