vhost_user.rst: Add GET_SHMEM_CONFIG message
Add GET_SHMEM_CONFIG vhost-user frontend message to the spec documentation. Reviewed-by: Stefano Garzarella <sgarzare@redhat.com> Reviewed-by: Alyssa Ross <hi@alyssa.is> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Albert Esteve <aesteve@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Message-Id: <20260304165223.2166175-6-aesteve@redhat.com>
Albert Esteve committed
Mar 4, 2026 at 17:52 UTC
060ed6a4bb4d50e3de257a29137e84843f069312
1 file changed
+39
docs/interop/vhost-user.rst
+39
@@ -384,6 +384,22 @@ MMAP request
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- 0: Pages are mapped read-only
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- 1: Pages are mapped read-write
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+VIRTIO Shared Memory Region configuration
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+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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+
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++-------------+---------+------------+----+--------------+
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+| num regions | padding | mem size 0 | .. | mem size 255 |
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++-------------+---------+------------+----+--------------+
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+
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+:num regions: a 32-bit number of regions
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+
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+:padding: 32-bit
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+
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+:mem size: an array of 256 64-bit fields representing the size of each
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+ VIRTIO Shared Memory Region. ``num regions`` specifies the
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+ number of valid regions (non-zero size). The array index
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+ corresponds to the shared memory ID (shmid).
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+
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C structure
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-----------
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@@ -410,6 +426,7 @@ In QEMU the vhost-user message is implemented with the following struct:
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VhostUserShared object;
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VhostUserTransferDeviceState transfer_state;
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VhostUserMMap mmap;
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+ VhostUserShMemConfig shmem;
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};
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} QEMU_PACKED VhostUserMsg;
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@@ -1794,6 +1811,28 @@ Front-end message types
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Using this function requires prior negotiation of the
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``VHOST_USER_PROTOCOL_F_DEVICE_STATE`` feature.
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+``VHOST_USER_GET_SHMEM_CONFIG``
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+ :id: 44
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+ :equivalent ioctl: N/A
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+ :request payload: N/A
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+ :reply payload: ``struct VhostUserShMemConfig``
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+
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+ When the ``VHOST_USER_PROTOCOL_F_SHMEM`` protocol feature has been
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+ successfully negotiated, this message can be submitted by the front-end
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+ to gather the VIRTIO Shared Memory Region configuration. The back-end will
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+ respond with the number of VIRTIO Shared Memory Regions it requires, and
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+ each shared memory region size in an array. The shared memory IDs are
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+ represented by the array index. The information returned shall comply
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+ with the following rules:
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+
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+ * The shared information will remain valid and unchanged for the entire
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+ lifetime of the connection.
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+
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+ * The Shared Memory Region size must be a multiple of the page size
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+ supported by mmap(2).
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+
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+ * The size may be 0 if the region is unused.
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+
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Back-end message types
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----------------------
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