Re: [Qemu-devel] [PATCH v4 12/22] vhost: only use shared log if in use by backend

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

On Sat, Sep 19, 2015 at 12:12:03PM +0200, marcandre.lureau@redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> Do not allocate a shared log if the backend doesn't support it.
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

If not there, we probably want to block live migration, correct?

> ---
>  hw/virtio/vhost-user.c            |  9 +++++++++
>  hw/virtio/vhost.c                 | 15 ++++++++++-----
>  include/hw/virtio/vhost-backend.h |  4 ++++
>  3 files changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 3cb5559..d12cd66 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -508,10 +508,19 @@ static int vhost_user_cleanup(struct vhost_dev *dev)
>      return 0;
>  }
>  
> +static bool vhost_user_want_shm_log(struct vhost_dev *dev)
> +{
> +    assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
> +
> +    return virtio_has_feature(dev->protocol_features,
> +                              VHOST_USER_PROTOCOL_F_LOG_SHMFD);
> +}
> +
>  const VhostOps user_ops = {
>          .backend_type = VHOST_BACKEND_TYPE_USER,
>          .vhost_backend_init = vhost_user_init,
>          .vhost_backend_cleanup = vhost_user_cleanup,
> +        .vhost_backend_want_shm_log = vhost_user_want_shm_log,
>  
>          .vhost_net_set_backend = vhost_net_set_backend,
>          .vhost_scsi_set_endpoint = vhost_scsi_set_endpoint,
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 0fa7b69..d5070fb 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -350,10 +350,15 @@ static void vhost_log_put(struct vhost_dev *dev, bool sync)
>      }
>  }
>  
> -static inline void vhost_dev_log_resize(struct vhost_dev* dev, uint64_t size)
> +static bool vhost_dev_log_is_shared(struct vhost_dev *dev)
>  {
> -    bool share = dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER;
> -    struct vhost_log *log = vhost_log_get(size, share);
> +    return dev->vhost_ops->vhost_backend_want_shm_log &&
> +           dev->vhost_ops->vhost_backend_want_shm_log(dev);
> +}
> +
> +static inline void vhost_dev_log_resize(struct vhost_dev *dev, uint64_t size)
> +{
> +    struct vhost_log *log = vhost_log_get(size, vhost_dev_log_is_shared(dev));
>      uint64_t log_base = (uintptr_t)log->log;
>      int r;
>  
> @@ -1161,10 +1166,10 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
>  
>      if (hdev->log_enabled) {
>          uint64_t log_base;
> -        bool share = hdev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER;
>  
>          hdev->log_size = vhost_get_log_size(hdev);
> -        hdev->log = vhost_log_get(hdev->log_size, share);
> +        hdev->log = vhost_log_get(hdev->log_size,
> +                                  vhost_dev_log_is_shared(hdev));
>          log_base = (uintptr_t)hdev->log->log;
>          r = hdev->vhost_ops->vhost_set_log_base(hdev,
>                                                  hdev->log_size ? log_base : 0,
> diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
> index a87f0b3..44bf200 100644
> --- a/include/hw/virtio/vhost-backend.h
> +++ b/include/hw/virtio/vhost-backend.h
> @@ -11,6 +11,8 @@
>  #ifndef VHOST_BACKEND_H_
>  #define VHOST_BACKEND_H_
>  
> +#include <stdbool.h>
> +
>  typedef enum VhostBackendType {
>      VHOST_BACKEND_TYPE_NONE = 0,
>      VHOST_BACKEND_TYPE_KERNEL = 1,
> @@ -28,6 +30,7 @@ struct vhost_scsi_target;
>  
>  typedef int (*vhost_backend_init)(struct vhost_dev *dev, void *opaque);
>  typedef int (*vhost_backend_cleanup)(struct vhost_dev *dev);
> +typedef bool (*vhost_backend_want_shm_log)(struct vhost_dev *dev);
>  
>  typedef int (*vhost_net_set_backend_op)(struct vhost_dev *dev,
>                                          struct vhost_vring_file *file);
> @@ -67,6 +70,7 @@ typedef struct VhostOps {
>  
>      vhost_backend_init vhost_backend_init;
>      vhost_backend_cleanup vhost_backend_cleanup;
> +    vhost_backend_want_shm_log vhost_backend_want_shm_log;
>  
>      vhost_net_set_backend_op vhost_net_set_backend;
>      vhost_scsi_set_endpoint_op vhost_scsi_set_endpoint;
> -- 
> 2.4.3