Re: [PATCH RFC 00/11] qemu: towards virtio-1 host support

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Oct 24, 2014 at 10:38:39AM +0200, Cornelia Huck wrote:
> On Fri, 24 Oct 2014 00:42:20 +0300
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Tue, Oct 07, 2014 at 04:39:56PM +0200, Cornelia Huck wrote:
> > > This patchset aims to get us some way to implement virtio-1 compliant
> > > and transitional devices in qemu. Branch available at
> > > 
> > > git://github.com/cohuck/qemu virtio-1
> > > 
> > > I've mainly focused on:
> > > - endianness handling
> > > - extended feature bits
> > > - virtio-ccw new/changed commands
> > 
> > So issues identified so far:
> 
> Thanks for taking a look.
> 
> > - devices not converted yet should not advertize 1.0
> 
> Neither should an uncoverted transport. So we either can
> - have transport set the bit and rely on devices ->get_features
>   callback to mask it out
>   (virtio-ccw has to change the calling order for get_features, btw.)
> - have device set the bit and the transport mask it out later. Feels a
>   bit weird, as virtio-1 is a transport feature bit.


I thought more about it, I think the right thing
would be for unconverted transports to clear
high bits on ack and get features.

So bit 32 is set, but not exposed to guests.
In fact at least for PCI, we have a 32 bit field for
features in 0.9 so it's automatic.
Didn't check mmio yet.



> I'm tending towards the first option; smth like this (on top of my
> branch):
> 
> diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
> index c29c8c8..f6501ea 100644
> --- a/hw/9pfs/virtio-9p-device.c
> +++ b/hw/9pfs/virtio-9p-device.c
> @@ -24,6 +24,9 @@
>  static uint32_t virtio_9p_get_features(VirtIODevice *vdev, unsigned int index,
>                                         uint32_t features)
>  {
> +    if (index == 1) {
> +        features &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
> +    }
>      if (index > 0) {
>          return features;
>      }
> diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
> index 0d843fe..07a7a6f 100644
> --- a/hw/char/virtio-serial-bus.c
> +++ b/hw/char/virtio-serial-bus.c
> @@ -472,6 +472,9 @@ static uint32_t get_features(VirtIODevice *vdev, unsigned int index,
>  {
>      VirtIOSerial *vser;
>  
> +    if (index == 1) {
> +        features &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
> +    }
>      if (index > 0) {
>          return features;
>      }
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 67f91c0..4b75105 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -447,6 +447,9 @@ static uint32_t virtio_net_get_features(VirtIODevice *vdev, unsigned int index,
>      VirtIONet *n = VIRTIO_NET(vdev);
>      NetClientState *nc = qemu_get_queue(n->nic);
>  
> +    if (index == 1 && get_vhost_net(nc->peer)) {
> +        features &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
> +    }
>      if (index > 0) {
>          return features;
>      }
> diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
> index 80efe88..07fbf40 100644
> --- a/hw/s390x/virtio-ccw.c
> +++ b/hw/s390x/virtio-ccw.c
> @@ -839,16 +839,16 @@ static int virtio_ccw_device_init(VirtioCcwDevice *dev, VirtIODevice *vdev)
>      dev->revision = -1;
>  
>      /* Set default feature bits that are offered by the host. */
> +    dev->host_features[0] = 0x1 << VIRTIO_F_NOTIFY_ON_EMPTY;
> +    dev->host_features[0] |= 0x1 << VIRTIO_F_BAD_FEATURE;
> +
> +    dev->host_features[1] = 1 << (VIRTIO_F_VERSION_1 - 32);
> +
>      for (i = 0; i < ARRAY_SIZE(dev->host_features); i++) {
>          dev->host_features[i] =
>              virtio_bus_get_vdev_features(&dev->bus, i, dev->host_features[i]);
>      }
>  
> -    dev->host_features[0] |= 0x1 << VIRTIO_F_NOTIFY_ON_EMPTY;
> -    dev->host_features[0] |= 0x1 << VIRTIO_F_BAD_FEATURE;
> -
> -    dev->host_features[1] = 1 << (VIRTIO_F_VERSION_1 - 32);
> -
>      css_generate_sch_crws(sch->cssid, sch->ssid, sch->schid,
>                            parent->hotplugged, 1);
>      return 0;
> diff --git a/hw/scsi/vhost-scsi.c b/hw/scsi/vhost-scsi.c
> index 8e1afa0..8a8fdb9 100644
> --- a/hw/scsi/vhost-scsi.c
> +++ b/hw/scsi/vhost-scsi.c
> @@ -155,6 +155,9 @@ static uint32_t vhost_scsi_get_features(VirtIODevice *vdev, unsigned int index,
>  {
>      VHostSCSI *s = VHOST_SCSI(vdev);
>  
> +    if (index == 1) {
> +        features &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
> +    }
>      if (index > 0) {
>          return features;
>      }
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 088e688..378783f 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -611,6 +611,9 @@ static void virtio_scsi_set_config(VirtIODevice *vdev,
>  static uint32_t virtio_scsi_get_features(VirtIODevice *vdev, unsigned int index,
>                                           uint32_t requested_features)
>  {
> +    if (index == 1) {
> +        requested_features &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
> +    }
>      return requested_features;
>  }
>  
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 5af17e2..bd52845 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -306,6 +306,9 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
>  static uint32_t virtio_balloon_get_features(VirtIODevice *vdev,
>                                              unsigned int index, uint32_t f)
>  {
> +    if (index == 1) {
> +        f &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
> +    }
>      if (index > 0) {
>          return f;
>      }
> diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c
> index 2814017..bf6101d 100644
> --- a/hw/virtio/virtio-rng.c
> +++ b/hw/virtio/virtio-rng.c
> @@ -101,6 +101,9 @@ static void handle_input(VirtIODevice *vdev, VirtQueue *vq)
>  
>  static uint32_t get_features(VirtIODevice *vdev, unsigned int index, uint32_t f)
>  {
> +    if (index == 1) {
> +        f &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
> +    }
>      return f;
>  }
>  
> 
> 
> > - blk has some features removed under 1.0,
> >   specifically CONFIG_WCE.
> > - net header is different for 1.0