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.. SPDX-License-Identifier: GPL-2.0-or-later
=========
vfio-user
=========
QEMU includes a ``vfio-user`` client. The ``vfio-user`` specification allows for
implementing (PCI) devices in userspace outside of QEMU; it is similar to
``vhost-user`` in this respect (see :doc:`vhost-user`), but can emulate arbitrary
PCI devices, not just ``virtio``. Whereas ``vfio`` is handled by the host
kernel, ``vfio-user``, while similar in implementation, is handled entirely in
userspace.
For example, SPDK includes a virtual PCI NVMe controller implementation; by
setting up a ``vfio-user`` UNIX socket between QEMU and SPDK, a VM can send NVMe
I/O to the SPDK process.
Presuming a suitable ``vfio-user`` server has opened a socket at
``/tmp/vfio-user.sock``, a device can be configured with for example:
.. code-block:: console
-device '{"driver": "vfio-user-pci","socket": {"path": "/tmp/vfio-user.sock", "type": "unix"}}'
See `libvfio-user <https://github.com/nutanix/libvfio-user/>`_ for further
information.
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