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Re: [Qemu-devel] [PATCH] virtio-bus: Plug devices after features are neg


From: Maxime Coquelin
Subject: Re: [Qemu-devel] [PATCH] virtio-bus: Plug devices after features are negotiated
Date: Tue, 13 Sep 2016 08:41:43 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0



On 09/12/2016 08:41 PM, Eric Blake wrote:
On 09/10/2016 03:23 AM, Maxime Coquelin wrote:
Currently, devices are plugged before features are negotiated.
If the backend doesn't support VIRTIO_F_VERSION_1, the transport
need to rewind some settings.

This is the case for CCW, for which a post_plugged callback had
been introduced, where max_rev field is just updated if
VIRTIO_F_VERSION_1 is not supported by the backend.
For PCI, implementing the post_plugged would be much more
complicated, so it needs to know whether the backend supports
VIRTIO_F_VERSION_1 at plug time.

Currently, nothing is done for PCI. Modern capabilitities get

s/capabilitities/capabilities/

exposed to the guest even if VIRTIO_F_VERSION_1 is not supported
by the backend, which confuses the guest.

This patch proposes to replace existing post_plugged solution
with an approach that fits with both transports.
Features negociation is performed before ->device_plugged() call.

s/negociation/negotiation/

Thanks Eric,
it will be fixed in next version.

Maxime



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