Re: [Qemu-devel] [PATCH 3/4] vhost-user: add protocol feature negotiation

[Flavio Leitner <fbl@redhat.com>]

On Fri, Jul 17, 2015 at 05:09:38PM +0300, Michael S. Tsirkin wrote:
> Support a separate bitmask for vhost-user protocol features,
> and messages to get/set protocol features.
> 
> Invoke them at init.
> 
> No features are defined yet.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  include/hw/virtio/vhost.h |  1 +
>  hw/net/vhost_net.c        |  2 ++
>  hw/virtio/vhost-user.c    | 52 +++++++++++++++++++++++++++++++++++++++++++++++
>  docs/specs/vhost-user.txt | 37 +++++++++++++++++++++++++++++++++
>  4 files changed, 92 insertions(+)
> 
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index dd51050..6467c73 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -47,6 +47,7 @@ struct vhost_dev {
>      unsigned long long features;
>      unsigned long long acked_features;
>      unsigned long long backend_features;
> +    unsigned long long protocol_features;
>      bool started;
>      bool log_enabled;
>      unsigned long long log_size;
> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> index 5c1d11f..c864237 100644
> --- a/hw/net/vhost_net.c
> +++ b/hw/net/vhost_net.c
> @@ -152,8 +152,10 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
>          net->dev.backend_features = qemu_has_vnet_hdr(options->net_backend)
>              ? 0 : (1ULL << VHOST_NET_F_VIRTIO_NET_HDR);
>          net->backend = r;
> +        net->dev.protocol_features = 0;
>      } else {
>          net->dev.backend_features = 0;
> +        net->dev.protocol_features = 0;
>          net->backend = -1;
>      }
>      net->nc = options->net_backend;
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 5a83d00..c4428a1 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -25,6 +25,9 @@
>  
>  #define VHOST_MEMORY_MAX_NREGIONS    8
>  
> +#define VHOST_USER_F_PROTOCOL_FEATURES 30
> +#define VHOST_USER_PROTOCOL_FEATURE_MASK 0x0ULL
> +
>  typedef enum VhostUserRequest {
>      VHOST_USER_NONE = 0,
>      VHOST_USER_GET_FEATURES = 1,
> @@ -41,6 +44,8 @@ typedef enum VhostUserRequest {
>      VHOST_USER_SET_VRING_KICK = 12,
>      VHOST_USER_SET_VRING_CALL = 13,
>      VHOST_USER_SET_VRING_ERR = 14,
> +    VHOST_USER_GET_PROTOCOL_FEATURES = 15,
> +    VHOST_USER_SET_PROTOCOL_FEATURES = 26,

I think you meant 16 here.
fbl


>      VHOST_USER_MAX
>  } VhostUserRequest;
>  
> @@ -332,10 +337,57 @@ static int vhost_user_call(struct vhost_dev *dev, unsigned long int request,
>  
>  static int vhost_user_init(struct vhost_dev *dev, void *opaque)
>  {
> +    VhostUserMsg msg = { 0 };
> +    int err;
> +
>      assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
>  
>      dev->opaque = opaque;
>  
> +    msg.request = VHOST_USER_GET_FEATURES;
> +    msg.flags = VHOST_USER_VERSION;
> +    msg.size = 0;
> +
> +    err = vhost_user_write(dev, &msg, NULL, 0);
> +    if (err < 0) {
> +        return err;
> +    }
> +
> +    err = vhost_user_read(dev, &msg);
> +    if (err < 0) {
> +        return err;
> +    }
> +
> +    if (__virtio_has_feature(msg.u64, VHOST_USER_F_PROTOCOL_FEATURES)) {
> +        dev->backend_features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
> +
> +        msg.request = VHOST_USER_GET_PROTOCOL_FEATURES;
> +        msg.flags = VHOST_USER_VERSION;
> +        msg.size = 0;
> +
> +        err = vhost_user_write(dev, &msg, NULL, 0);
> +        if (err < 0) {
> +            return err;
> +        }
> +
> +        err = vhost_user_read(dev, &msg);
> +        if (err < 0) {
> +            return err;
> +        }
> +
> +        dev->protocol_features = msg.u64 & VHOST_USER_PROTOCOL_FEATURE_MASK;
> +
> +        msg.request = VHOST_USER_SET_PROTOCOL_FEATURES;
> +        msg.flags = VHOST_USER_VERSION;
> +        msg.u64 = dev->protocol_features;
> +        msg.size = sizeof msg.u64;
> +
> +        err = vhost_user_write(dev, &msg, NULL, 0);
> +        if (err < 0) {
> +            return err;
> +        }
> +    }
> +
>      return 0;
>  }
>  
> diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
> index 650bb18..0062baa 100644
> --- a/docs/specs/vhost-user.txt
> +++ b/docs/specs/vhost-user.txt
> @@ -113,6 +113,7 @@ message replies. Most of the requests don't require replies. Here is a list of
>  the ones that do:
>  
>   * VHOST_GET_FEATURES
> + * VHOST_GET_PROTOCOL_FEATURES
>   * VHOST_GET_VRING_BASE
>  
>  There are several messages that the master sends with file descriptors passed
> @@ -127,6 +128,13 @@ in the ancillary data:
>  If Master is unable to send the full message or receives a wrong reply it will
>  close the connection. An optional reconnection mechanism can be implemented.
>  
> +Any protocol extensions are gated by protocol feature bits,
> +which allows full backwards compatibility on both master
> +and slave.
> +As older slaves don't support negotiating protocol features,
> +a feature bit was dedicated for this purpose:
> +#define VHOST_USER_F_PROTOCOL_FEATURES 30
> +
>  Message types
>  -------------
>  
> @@ -138,6 +146,8 @@ Message types
>        Slave payload: u64
>  
>        Get from the underlying vhost implementation the features bitmask.
> +      Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals slave support for
> +      VHOST_USER_GET_PROTOCOL_FEATURES and VHOST_USER_SET_PROTOCOL_FEATURES.
>  
>   * VHOST_USER_SET_FEATURES
>  
> @@ -146,6 +156,33 @@ Message types
>        Master payload: u64
>  
>        Enable features in the underlying vhost implementation using a bitmask.
> +      Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals master support for
> +      VHOST_USER_GET_PROTOCOL_FEATURES and VHOST_USER_SET_PROTOCOL_FEATURES.
> +
> + * VHOST_USER_GET_PROTOCOL_FEATURES
> +
> +      Id: 15
> +      Equivalent ioctl: VHOST_GET_FEATURES
> +      Master payload: N/A
> +      Slave payload: u64
> +
> +      Get the protocol feature bitmask from the underlying vhost implementation.
> +      Only legal if feature bit VHOST_USER_F_PROTOCOL_FEATURES is present in
> +      VHOST_USER_GET_FEATURES.
> +      Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must support
> +      this message even before VHOST_USER_SET_FEATURES was called.
> +
> + * VHOST_USER_SET_PROTOCOL_FEATURES
> +
> +      Id: 16
> +      Ioctl: VHOST_SET_FEATURES
> +      Master payload: u64
> +
> +      Enable protocol features in the underlying vhost implementation.
> +      Only legal if feature bit VHOST_USER_F_PROTOCOL_FEATURES is present in
> +      VHOST_USER_GET_FEATURES.
> +      Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must support
> +      this message even before VHOST_USER_SET_FEATURES was called.
>  
>   * VHOST_USER_SET_OWNER
>  
> -- 
> MST
>