Albert Esteve <aest...@redhat.com> writes: > Add SHMEM_MAP/_UNMAP request to the vhost-user > spec documentation. > > Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com> > Signed-off-by: Albert Esteve <aest...@redhat.com> > --- > docs/interop/vhost-user.rst | 55 +++++++++++++++++++++++++++++++++++++ > 1 file changed, 55 insertions(+) > > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst > index 436a94c0ee..b623284819 100644 > --- a/docs/interop/vhost-user.rst > +++ b/docs/interop/vhost-user.rst > @@ -350,6 +350,27 @@ Device state transfer parameters > In the future, additional phases might be added e.g. to allow > iterative migration while the device is running. > > +MMAP request > +^^^^^^^^^^^^ > + > ++-------+---------+-----------+------------+-----+-------+ > +| shmid | padding | fd_offset | shm_offset | len | flags | > ++-------+---------+-----------+------------+-----+-------+ > + > +:shmid: a 8-bit shared memory region identifier > + > +:fd_offset: a 64-bit offset of this area from the start > + of the supplied file descriptor > + > +:shm_offset: a 64-bit offset from the start of the > + pointed shared memory region > + > +:len: a 64-bit size of the memory to map > + > +:flags: a 64-bit value: > + - 0: Pages are mapped read-only > + - 1: Pages are mapped read-write > + > C structure > ----------- > > @@ -375,6 +396,7 @@ In QEMU the vhost-user message is implemented with the > following struct: > VhostUserInflight inflight; > VhostUserShared object; > VhostUserTransferDeviceState transfer_state; > + VhostUserMMap mmap; > }; > } QEMU_PACKED VhostUserMsg; > > @@ -1057,6 +1079,7 @@ Protocol features > #define VHOST_USER_PROTOCOL_F_XEN_MMAP 17 > #define VHOST_USER_PROTOCOL_F_SHARED_OBJECT 18 > #define VHOST_USER_PROTOCOL_F_DEVICE_STATE 19 > + #define VHOST_USER_PROTOCOL_F_SHMEM 20 > > Front-end message types > ----------------------- > @@ -1865,6 +1888,38 @@ is sent by the front-end. > when the operation is successful, or non-zero otherwise. Note that if the > operation fails, no fd is sent to the backend. > > +``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``. A reply is > + generated indicating whether mapping succeeded.
Should this be phrased to make it clear replies are only generated in
some cases, like how e.g. VHOST_USER_BACKEND_IOTLB_MSG phrases it?
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 request shall fail.
request*s* 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.
> +
> +``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-mmap a given range (``shm_offset``, ``len``) in the
un-mmaps?
> + 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.
> +
> .. _reply_ack:
>
> VHOST_USER_PROTOCOL_F_REPLY_ACK
> --
> 2.49.0
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