Re: [Qemu-devel] [PATCH v2 2/2] vhost-user: back SET/GET_CONFIG requests with a protocol feature

[Liu, Changpeng]

> -----Original Message-----
> From: Maxime Coquelin [mailto:address@hidden
> Sent: Thursday, March 29, 2018 3:28 AM
> To: address@hidden; Liu, Changpeng <address@hidden>;
> address@hidden; address@hidden
> Cc: Maxime Coquelin <address@hidden>
> Subject: [PATCH v2 2/2] vhost-user: back SET/GET_CONFIG requests with a
> protocol feature
> 
> Without a dedicated protocol feature, QEMU cannot know whether
> the backend can handle VHOST_USER_SET_CONFIG and
> VHOST_USER_GET_CONFIG messages.
> 
> This patch adds a protocol feature that is only advertised by
> QEMU if the device implements the config ops. Vhost user init
> fails if the device support the feature but the backend doesn't.
> 
> The backend should only send VHOST_USER_SLAVE_CONFIG_CHANGE_MSG
> requests if the protocol feature has been negotiated.
> 
> Signed-off-by: Maxime Coquelin <address@hidden>

Passed our own vhost-user-blk target with the patch, I can submit a fix to QEMU 
vhost-user-blk example
after this commit.

Tested-by: Changpeng Liu <address@hidden>
> ---
>  docs/interop/vhost-user.txt | 21 ++++++++++++---------
>  hw/virtio/vhost-user.c      | 22 ++++++++++++++++++++++
>  2 files changed, 34 insertions(+), 9 deletions(-)
> 
> diff --git a/docs/interop/vhost-user.txt b/docs/interop/vhost-user.txt
> index c058c407df..534caab18a 100644
> --- a/docs/interop/vhost-user.txt
> +++ b/docs/interop/vhost-user.txt
> @@ -379,6 +379,7 @@ Protocol features
>  #define VHOST_USER_PROTOCOL_F_CROSS_ENDIAN   6
>  #define VHOST_USER_PROTOCOL_F_CRYPTO_SESSION 7
>  #define VHOST_USER_PROTOCOL_F_PAGEFAULT      8
> +#define VHOST_USER_PROTOCOL_F_CONFIG         9
> 
>  Master message types
>  --------------------
> @@ -664,7 +665,8 @@ Master message types
>        Master payload: virtio device config space
>        Slave payload: virtio device config space
> 
> -      Submitted by the vhost-user master to fetch the contents of the virtio
> +      When VHOST_USER_PROTOCOL_F_CONFIG is negotiated, this message is
> +      submitted by the vhost-user master to fetch the contents of the virtio
>        device configuration space, vhost-user slave's payload size MUST match
>        master's request, vhost-user slave uses zero length of payload to
>        indicate an error to vhost-user master. The vhost-user master may
> @@ -677,7 +679,8 @@ Master message types
>        Master payload: virtio device config space
>        Slave payload: N/A
> 
> -      Submitted by the vhost-user master when the Guest changes the virtio
> +      When VHOST_USER_PROTOCOL_F_CONFIG is negotiated, this message is
> +      submitted by the vhost-user master when the Guest changes the virtio
>        device configuration space and also can be used for live migration
>        on the destination host. The vhost-user slave must check the flags
>        field, and slaves MUST NOT accept SET_CONFIG for read-only
> @@ -766,13 +769,13 @@ Slave message types
>       Slave payload: N/A
>       Master payload: N/A
> 
> -     Vhost-user slave sends such messages to notify that the virtio device's
> -     configuration space has changed, for those host devices which can 
> support
> -     such feature, host driver can send VHOST_USER_GET_CONFIG message to
> slave
> -     to get the latest content. If VHOST_USER_PROTOCOL_F_REPLY_ACK is
> -     negotiated, and slave set the VHOST_USER_NEED_REPLY flag, master must
> -     respond with zero when operation is successfully completed, or non-zero
> -     otherwise.
> +     When VHOST_USER_PROTOCOL_F_CONFIG is negotiated, vhost-user slave
> sends
> +     such messages to notify that the virtio device's configuration space has
> +     changed, for those host devices which can support such feature, host
> +     driver can send VHOST_USER_GET_CONFIG message to slave to get the latest
> +     content. If VHOST_USER_PROTOCOL_F_REPLY_ACK is negotiated, and slave
> set
> +     the VHOST_USER_NEED_REPLY flag, master must respond with zero when
> +     operation is successfully completed, or non-zero otherwise.
> 
>  VHOST_USER_PROTOCOL_F_REPLY_ACK:
>  -------------------------------
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 44aea5c0a8..cc8a24aa31 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -46,6 +46,7 @@ enum VhostUserProtocolFeature {
>      VHOST_USER_PROTOCOL_F_CROSS_ENDIAN = 6,
>      VHOST_USER_PROTOCOL_F_CRYPTO_SESSION = 7,
>      VHOST_USER_PROTOCOL_F_PAGEFAULT = 8,
> +    VHOST_USER_PROTOCOL_F_CONFIG = 9,
>      VHOST_USER_PROTOCOL_F_MAX
>  };
> 
> @@ -1211,6 +1212,17 @@ static int vhost_user_init(struct vhost_dev *dev, void
> *opaque)
> 
>          dev->protocol_features =
>              protocol_features & VHOST_USER_PROTOCOL_FEATURE_MASK;
> +
> +        if (!dev->config_ops || !dev->config_ops->vhost_dev_config_notifier) 
> {
> +            /* Dont acknowledge CONFIG feature if device doesn't support it 
> */
> +            dev->protocol_features &= ~(1ULL <<
> VHOST_USER_PROTOCOL_F_CONFIG);
> +        } else if (!(protocol_features &
> +                    (1ULL << VHOST_USER_PROTOCOL_F_CONFIG))) {
> +            error_report("Device expects VHOST_USER_PROTOCOL_F_CONFIG "
> +                    "but backend does not support it.");
> +            return -1;
> +        }
> +
>          err = vhost_user_set_protocol_features(dev, dev->protocol_features);
>          if (err < 0) {
>              return err;
> @@ -1405,6 +1417,11 @@ static int vhost_user_get_config(struct vhost_dev
> *dev, uint8_t *config,
>          .hdr.size = VHOST_USER_CONFIG_HDR_SIZE + config_len,
>      };
> 
> +    if (!virtio_has_feature(dev->protocol_features,
> +                VHOST_USER_PROTOCOL_F_CONFIG)) {
> +        return -1;
> +    }
> +
>      if (config_len > VHOST_USER_MAX_CONFIG_SIZE) {
>          return -1;
>      }
> @@ -1448,6 +1465,11 @@ static int vhost_user_set_config(struct vhost_dev
> *dev, const uint8_t *data,
>          .hdr.size = VHOST_USER_CONFIG_HDR_SIZE + size,
>      };
> 
> +    if (!virtio_has_feature(dev->protocol_features,
> +                VHOST_USER_PROTOCOL_F_CONFIG)) {
> +        return -1;
> +    }
> +
>      if (reply_supported) {
>          msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
>      }
> --
> 2.14.3