Re: [PATCH v12 3/7] vhost_user.rst: Add SHMEM_MAP/_UNMAP to spec

[Alyssa Ross <hi@alyssa.is>]

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Albert Esteve <aesteve@redhat.com> writes:

> +``VHOST_USER_BACKEND_SHMEM_MAP``
> +  :id: 9
> +  :equivalent ioctl: N/A
> +  :request payload: fd and ``struct VhostUserMMap``
> +  :reply payload: N/A
> +
> +  When the ``VHOST_USER_PROTOCOL_F_SHMEM`` protocol feature has been
> +  successfully negotiated, this message can be submitted by the backends to
> +  advertise a new mapping to be made in a given VIRTIO Shared Memory Region.
> +  Upon receiving the message, the front-end will mmap the given fd into the
> +  VIRTIO Shared Memory Region with the requested ``shmid``.
> +  If ``VHOST_USER_PROTOCOL_F_REPLY_ACK`` is negotiated, and
> +  back-end set the ``VHOST_USER_NEED_REPLY`` flag, the front-end
> +  must respond with zero when operation is successfully completed,
> +  or non-zero otherwise.
> +
> +  Mapping over an already existing map is not allowed and requests shall fail.
> +  Therefore, the memory range in the request must correspond with a valid,
> +  free region of the VIRTIO Shared Memory Region. Also, note that mappings
> +  consume resources and that the request can fail when there are no resources
> +  available. Lastly, mappings are automatically unmapped by the front-end
> +  across device reset operation.
> +
> +``VHOST_USER_BACKEND_SHMEM_UNMAP``
> +  :id: 10
> +  :equivalent ioctl: N/A
> +  :request payload: ``struct VhostUserMMap``
> +  :reply payload: N/A
> +
> +  When the ``VHOST_USER_PROTOCOL_F_SHMEM`` protocol feature has been
> +  successfully negotiated, this message can be submitted by the backends so
> +  that the front-end un-mmaps a given range (``shm_offset``, ``len``) in the
> +  VIRTIO Shared Memory Region with the requested ``shmid``. Note that the
> +  given range shall correspond to the entirety of a valid mapped region.
> +  A reply is generated indicating whether unmapping succeeded.

Shouldn't this be phrased like VHOST_USER_BACKEND_SHMEM_MAP above,
since as we've established replies are only generated if negotiated?

  If ``VHOST_USER_PROTOCOL_F_REPLY_ACK`` is negotiated, and the back-end
  sets the ``VHOST_USER_NEED_REPLY`` flag, the front-end must respond with
  zero when operation is successfully completed, or non-zero otherwise.

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