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virtio-bus: Plug devices after features are negotiated

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Currently, devices are plugged before features are negotiated.
If the backend doesn't support VIRTIO_F_VERSION_1, the transport
needs 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 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 capabilities get
exposed to the guest even if VIRTIO_F_VERSION_1 is not supported
by the backend, which confuses the guest.

This patch replaces existing post_plugged solution with an
approach that fits with both transports.
Features negotiation is performed before ->device_plugged() call.
A pre_plugged callback is introduced so that the transports can
set their supported features.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: qemu-stable@nongnu.org
Tested-by: Cornelia Huck <cornelia.huck@de.ibm.com> [ccw]
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
This commit is contained in:
Maxime Coquelin 2016-09-13 15:30:30 +02:00 • committed by Michael S. Tsirkin
parent d1eb8f2acb
commit d1b4259f1a
5 changed files with 62 additions and 28 deletions
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10
include/hw/virtio/virtio-bus.h
View file

@ -53,16 +53,16 @@ typedef struct VirtioBusClass {
bool (*query_guest_notifiers)(DeviceState *d);
int (*set_guest_notifiers)(DeviceState *d, int nvqs, bool assign);
void (*vmstate_change)(DeviceState *d, bool running);
/*
* Expose the features the transport layer supports before
* the negotiation takes place.
*/
void (*pre_plugged)(DeviceState *d, Error **errp);
/*
* transport independent init function.
* This is called by virtio-bus just after the device is plugged.
*/
void (*device_plugged)(DeviceState *d, Error **errp);
/*
* Re-evaluate setup after feature bits have been validated
* by the device backend.
*/
void (*post_plugged)(DeviceState *d, Error **errp);
/*
* transport independent exit function.
* This is called by virtio-bus just before the device is unplugged.