[PATCH v2 00/13] virtio: add vhost-user-generic and reduce copy and paste

[Alex Bennée]

A lot of our vhost-user stubs are large chunks of boilerplate that do
(mostly) the same thing. This series attempts to fix that by defining
a new base class (vhost-user-base) which is used by a generic
vhost-user-device implementation. Then the rng, gpio and i2c
vhost-user devices become simple specialisations of the common base
defining the ID, number of queues and potentially the config handling.

In theory we could convert the rest of the vhost-user stubs but there
are complications caused by the config being split between the daemon
and QEMU. For example:

 -device vhost-user-device-pci,chardev=vus,virtio-id=8,num_vqs=3,config_size=36

works with the WIP vhost-user-scsi backend:

  https://github.com/rust-vmm/vhost-device/pull/301

but the concrete vhost-user-scsi-pci device fails because it expects
to handle config via the command line. You will see the report:

  qemu-system-aarch64: -device vhost-user-scsi-pci,chardev=vus:
  warning: vhost-user backend supports VHOST_USER_PROTOCOL_F_CONFIG
  but QEMU does not.

if you try. We could make the device a bit smarter but then we would
need to untangle the vhost_scsi_common_() logic which is shared with
the pure in kernel vhost implementation. The vhost-user-vsock stub
might be another one worth re-factoring although that has a similar
split architecture.

The overall diffstat shows a net deletion of code as well as
introducing some more documentation and moving the stubs into the
common build, further reducing redundancy.

Next Steps
----------

>From Stefan's last email to the v1 posting we need:

vhost-user needs:
- A GET_DEVICE_ID message.
- A GET_CONFIG_SIZE message. Today it is assumed that the vhost-user
  frontend already knows the configuration space size.
- A protocol feature bit indicating that the device is a full VIRTIO
  device. These devices also need to implement the SET_STATUS message,
  which is rarely implemented today.

and implementing the VHOST_USER_GET_QUEUE_NUM and SET_STATUS messages
to make the generic device "self configuring".

Alex.

Alex Bennée (13):
  include: attempt to document device_class_set_props
  include/hw: document the device_class_set_parent_* fns
  hw/virtio: fix typo in VIRTIO_CONFIG_IRQ_IDX comments
  include/hw/virtio: document virtio_notify_config
  include/hw/virtio: add kerneldoc for virtio_init
  include/hw/virtio: document some more usage of notifiers
  virtio: add vhost-user-base and a generic vhost-user-device
  virtio: add PCI stub for vhost-user-device
  hw/virtio: derive vhost-user-rng from vhost-user-device
  hw/virtio: add config support to vhost-user-device
  hw/virtio: derive vhost-user-gpio from vhost-user-device
  hw/virtio: derive vhost-user-i2c from vhost-user-base
  docs/system: add a basic enumeration of vhost-user devices

 docs/system/devices/vhost-user-rng.rst |   2 +
 docs/system/devices/vhost-user.rst     |  41 +++
 include/hw/qdev-core.h                 |  36 +++
 include/hw/virtio/vhost-user-device.h  |  46 +++
 include/hw/virtio/vhost-user-gpio.h    |  23 +-
 include/hw/virtio/vhost-user-i2c.h     |  18 +-
 include/hw/virtio/vhost-user-rng.h     |  11 +-
 include/hw/virtio/virtio.h             |  21 ++
 hw/display/vhost-user-gpu.c            |   4 +-
 hw/net/virtio-net.c                    |   4 +-
 hw/virtio/vhost-user-device-pci.c      |  71 +++++
 hw/virtio/vhost-user-device.c          | 380 +++++++++++++++++++++++
 hw/virtio/vhost-user-fs.c              |   4 +-
 hw/virtio/vhost-user-gpio.c            | 400 ++-----------------------
 hw/virtio/vhost-user-i2c.c             | 255 +---------------
 hw/virtio/vhost-user-rng.c             | 277 ++---------------
 hw/virtio/vhost-vsock-common.c         |   4 +-
 hw/virtio/virtio-crypto.c              |   4 +-
 hw/virtio/meson.build                  |  20 +-
 19 files changed, 686 insertions(+), 935 deletions(-)
 create mode 100644 include/hw/virtio/vhost-user-device.h
 create mode 100644 hw/virtio/vhost-user-device-pci.c
 create mode 100644 hw/virtio/vhost-user-device.c

-- 
2.39.2