Re: [Qemu-devel] [PATCH 2/7] vhost-user: add protocol feature negotiation

[Jason Wang]

On 09/15/2015 03:10 PM, Yuanhan Liu wrote:
> From: "Michael S. Tsirkin" <address@hidden>
>
> 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.
>
> v2: leverage vhost_user_call for request handling -- Yuanhan Liu
>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> Signed-off-by: Yuanhan Liu <address@hidden>
> ---
>  docs/specs/vhost-user.txt | 37 +++++++++++++++++++++++++++++++++++++
>  hw/net/vhost_net.c        |  2 ++
>  hw/virtio/vhost-user.c    | 31 +++++++++++++++++++++++++++++++
>  include/hw/virtio/vhost.h |  1 +
>  4 files changed, 71 insertions(+)
>
> diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
> index 650bb18..70da3b1 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 slave 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
>  
> 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 13677ac..43169a1 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -24,6 +24,8 @@
>  #include <linux/vhost.h>
>  
>  #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,
> @@ -41,6 +43,8 @@ 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 = 16,
>      VHOST_USER_MAX
>  } VhostUserRequest;
>  
> @@ -206,11 +210,13 @@ static int vhost_user_call(struct vhost_dev *dev, 
> unsigned long int request,
>  
>      switch (msg_request) {
>      case VHOST_USER_GET_FEATURES:
> +    case VHOST_USER_GET_PROTOCOL_FEATURES:
>          need_reply = 1;
>          break;
>  
>      case VHOST_USER_SET_FEATURES:
>      case VHOST_USER_SET_LOG_BASE:
> +    case VHOST_USER_SET_PROTOCOL_FEATURES:
>          msg.u64 = *((__u64 *) arg);
>          msg.size = sizeof(m.u64);
>          break;
> @@ -308,6 +314,7 @@ static int vhost_user_call(struct vhost_dev *dev, 
> unsigned long int request,
>  
>          switch (msg_request) {
>          case VHOST_USER_GET_FEATURES:
> +        case VHOST_USER_GET_PROTOCOL_FEATURES:
>              if (msg.size != sizeof(m.u64)) {
>                  error_report("Received bad msg size.");
>                  return -1;
> @@ -333,10 +340,34 @@ static int vhost_user_call(struct vhost_dev *dev, 
> unsigned long int request,
>  
>  static int vhost_user_init(struct vhost_dev *dev, void *opaque)
>  {
> +    unsigned long long features;
> +    int err;
> +
>      assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
>  
>      dev->opaque = opaque;
>  
> +    err = vhost_user_call(dev, VHOST_USER_GET_FEATURES, &features);
> +    if (err < 0) {
> +        return err;
> +    }
> +
> +    if (__virtio_has_feature(features, VHOST_USER_F_PROTOCOL_FEATURES)) {

Need rebase to master. (And use virtio_has_feature() here).

> +        dev->backend_features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
> +
> +        err = vhost_user_call(dev, VHOST_USER_GET_PROTOCOL_FEATURES, 
> &features);
> +        if (err < 0) {
> +            return err;
> +        }
> +
> +        dev->protocol_features = features & VHOST_USER_PROTOCOL_FEATURE_MASK;
> +        err = vhost_user_call(dev, VHOST_USER_SET_PROTOCOL_FEATURES,
> +                              &dev->protocol_features);
> +        if (err < 0) {
> +            return err;
> +        }
> +    }
> +
>      return 0;
>  }
>  
> 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;