Re: [PATCH v4 4/9] vhost_user: Add frontend get_shmem_config command

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Feb 17, 2025 at 05:40:07PM +0100, Albert Esteve wrote:
> The frontend can use this command to retrieve
> VirtIO Shared Memory Regions configuration from
> the backend. The response contains the number of
> shared memory regions, their size, and shmid.
> 
> This is useful when the frontend is unaware of
> specific backend type and configuration,
> for example, in the `vhost-user-device` case.
> 
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
>  hw/virtio/vhost-user.c            | 43 +++++++++++++++++++++++++++++++
>  include/hw/virtio/vhost-backend.h |  9 +++++++
>  include/hw/virtio/vhost-user.h    |  1 +
>  include/hw/virtio/virtio.h        |  2 ++
>  4 files changed, 55 insertions(+)
> 
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index d88e6f8c3c..9cc148f726 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -104,6 +104,7 @@ typedef enum VhostUserRequest {
>      VHOST_USER_GET_SHARED_OBJECT = 41,
>      VHOST_USER_SET_DEVICE_STATE_FD = 42,
>      VHOST_USER_CHECK_DEVICE_STATE = 43,
> +    VHOST_USER_GET_SHMEM_CONFIG = 44,
>      VHOST_USER_MAX
>  } VhostUserRequest;
>  
> @@ -138,6 +139,12 @@ typedef struct VhostUserMemRegMsg {
>      VhostUserMemoryRegion region;
>  } VhostUserMemRegMsg;
>  
> +typedef struct VhostUserShMemConfig {
> +    uint32_t nregions;
> +    uint32_t padding;
> +    uint64_t memory_sizes[VIRTIO_MAX_SHMEM_REGIONS];
> +} VhostUserShMemConfig;
> +
>  typedef struct VhostUserLog {
>      uint64_t mmap_size;
>      uint64_t mmap_offset;
> @@ -245,6 +252,7 @@ typedef union {
>          VhostUserShared object;
>          VhostUserTransferDeviceState transfer_state;
>          VhostUserMMap mmap;
> +        VhostUserShMemConfig shmem;
>  } VhostUserPayload;
>  
>  typedef struct VhostUserMsg {
> @@ -3146,6 +3154,40 @@ static int vhost_user_check_device_state(struct vhost_dev *dev, Error **errp)
>      return 0;
>  }
>  
> +static int vhost_user_get_shmem_config(struct vhost_dev *dev,
> +                                       int *nregions,
> +                                       uint64_t *memory_sizes,
> +                                       Error **errp)
> +{
> +    int ret;
> +    VhostUserMsg msg = {
> +        .hdr.request = VHOST_USER_GET_SHMEM_CONFIG,
> +        .hdr.flags = VHOST_USER_VERSION,
> +    };
> +
> +    if (!virtio_has_feature(dev->protocol_features,
> +                            VHOST_USER_PROTOCOL_F_SHMEM)) {
> +        return 0;
> +    }
> +
> +    ret = vhost_user_write(dev, &msg, NULL, 0);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    ret = vhost_user_read(dev, &msg);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    assert(msg.payload.shmem.nregions <= VIRTIO_MAX_SHMEM_REGIONS);
> +    *nregions = msg.payload.shmem.nregions;
> +    memcpy(memory_sizes,
> +           &msg.payload.shmem.memory_sizes,
> +           sizeof(uint64_t) * VHOST_MEMORY_BASELINE_NREGIONS);

Should this be VIRTIO_MAX_SHMEM_REGIONS instead of
VHOST_MEMORY_BASELINE_NREGIONS?

> +    return 0;
> +}
> +
>  const VhostOps user_ops = {
>          .backend_type = VHOST_BACKEND_TYPE_USER,
>          .vhost_backend_init = vhost_user_backend_init,
> @@ -3184,4 +3226,5 @@ const VhostOps user_ops = {
>          .vhost_supports_device_state = vhost_user_supports_device_state,
>          .vhost_set_device_state_fd = vhost_user_set_device_state_fd,
>          .vhost_check_device_state = vhost_user_check_device_state,
> +        .vhost_get_shmem_config = vhost_user_get_shmem_config,
>  };
> diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
> index 70c2e8ffee..b40d82a111 100644
> --- a/include/hw/virtio/vhost-backend.h
> +++ b/include/hw/virtio/vhost-backend.h
> @@ -159,6 +159,14 @@ typedef int (*vhost_set_device_state_fd_op)(struct vhost_dev *dev,
>                                              int *reply_fd,
>                                              Error **errp);
>  typedef int (*vhost_check_device_state_op)(struct vhost_dev *dev, Error **errp);
> +/*
> + * Max regions is VIRTIO_MAX_SHMEM_REGIONS, so that is the maximum
> + * number of memory_sizes that will be accepted. */
> +typedef int (*vhost_get_shmem_config_op)(struct vhost_dev *dev,
> +                                         int *nregions,
> +                                         uint64_t *memory_sizes,
> +                                         Error **errp);
> +
>  
>  typedef struct VhostOps {
>      VhostBackendType backend_type;
> @@ -214,6 +222,7 @@ typedef struct VhostOps {
>      vhost_supports_device_state_op vhost_supports_device_state;
>      vhost_set_device_state_fd_op vhost_set_device_state_fd;
>      vhost_check_device_state_op vhost_check_device_state;
> +    vhost_get_shmem_config_op vhost_get_shmem_config;
>  } VhostOps;
>  
>  int vhost_backend_update_device_iotlb(struct vhost_dev *dev,
> diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
> index 9a3f238b43..bacc7d184c 100644
> --- a/include/hw/virtio/vhost-user.h
> +++ b/include/hw/virtio/vhost-user.h
> @@ -32,6 +32,7 @@ enum VhostUserProtocolFeature {
>      /* Feature 17 reserved for VHOST_USER_PROTOCOL_F_XEN_MMAP. */
>      VHOST_USER_PROTOCOL_F_SHARED_OBJECT = 18,
>      VHOST_USER_PROTOCOL_F_DEVICE_STATE = 19,
> +    VHOST_USER_PROTOCOL_F_SHMEM = 20,
>      VHOST_USER_PROTOCOL_F_MAX
>  };
>  
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index a778547c79..319e2f5b06 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -81,6 +81,8 @@ typedef struct VirtQueueElement
>  
>  #define VIRTIO_NO_VECTOR 0xffff
>  
> +#define VIRTIO_MAX_SHMEM_REGIONS 256
> +
>  /* special index value used internally for config irqs */
>  #define VIRTIO_CONFIG_IRQ_IDX -1
>  
> -- 
> 2.48.1
> 

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