vfio-user: add vfio-user class and container

MAINTAINERS

@@ -4246,13 +4246,22 @@ F: hw/remote/proxy-memory-listener.c
 F: include/hw/remote/proxy-memory-listener.h
 F: hw/remote/iohub.c
 F: include/hw/remote/iohub.h
-F: subprojects/libvfio-user
 F: hw/remote/vfio-user-obj.c
 F: include/hw/remote/vfio-user-obj.h
 F: hw/remote/iommu.c
 F: include/hw/remote/iommu.h
 F: tests/functional/test_multiprocess.py
 
+VFIO-USER:
+M: John Levon <john.levon@nutanix.com>
+M: Thanos Makatos <thanos.makatos@nutanix.com>
+S: Supported
+F: docs/interop/vfio-user.rst
+F: docs/system/devices/vfio-user.rst
+F: hw/vfio-user/*
+F: include/hw/vfio-user/*
+F: subprojects/libvfio-user
+
 EBPF:
 M: Jason Wang <jasowang@redhat.com>
 R: Andrew Melnychenko <andrew@daynix.com>

docs/interop/index.rst

@@ -25,6 +25,7 @@ are useful for making QEMU interoperate with other software.
    qemu-ga-ref
    qemu-qmp-ref
    qemu-storage-daemon-qmp-ref
+   vfio-user
    vhost-user
    vhost-user-gpu
    vhost-vdpa

docs/system/device-emulation.rst

@@ -85,6 +85,7 @@ Emulated Devices
    devices/can.rst
    devices/ccid.rst
    devices/cxl.rst
+   devices/vfio-user.rst
    devices/ivshmem.rst
    devices/ivshmem-flat.rst
    devices/keyboard.rst

docs/system/devices/vfio-user.rst

@@ -0,0 +1,26 @@
+.. 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.

hw/Kconfig

@@ -42,6 +42,7 @@ source ufs/Kconfig
 source usb/Kconfig
 source virtio/Kconfig
 source vfio/Kconfig
+source vfio-user/Kconfig
 source vmapple/Kconfig
 source xen/Kconfig
 source watchdog/Kconfig

hw/meson.build

@@ -39,6 +39,7 @@ subdir('uefi')
 subdir('ufs')
 subdir('usb')
 subdir('vfio')
+subdir('vfio-user')
 subdir('virtio')
 subdir('vmapple')
 subdir('watchdog')

hw/vfio-user/Kconfig

@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+config VFIO_USER
+    bool
+    default y
+    depends on VFIO_PCI
+