[PATCH v2 0/8] hw/usb: Add a usbredir server transport

[Jamin Lin <jamin_lin@aspeedtech.com>]

This series adds a usbredir server transport to redirect a USB device
emulated in one QEMU instance to a USB host controller emulated in
another one over the usbredir protocol.

The v1 series included both the usbredir server transport and the ASPEED
AST1030 USB Device Controller (UDC) support. Following review feedback,
this series contains only the usbredir server transport. The ASPEED
AST1030 UDC support will be sent separately.

This work is part of a larger plan to model USB device-side support on
ASPEED BMC/BIC SoCs, which has three goals:

1. Model the ASPEED UDC (AST2600 / AST1030). The AST2600 also has USB host
   (EHCI) controllers, so that work targets the AST2600 UDC: its gadget can
   be attached to the SoC's own EHCI bus, letting the guest enumerate its
   own gadget and exercise the UDC end-to-end.  [Done]
   https://lore.kernel.org/qemu-devel/20260902021542.3194812-1-jamin_lin@aspeedtech.com/

2. AST1030 UDC. The AST1030 has no USB host controller, so testing its UDC
   needs a second QEMU instance. The UDC gadget is redirected out of the
   guest with libusbredir and attached to another QEMU that runs a USB host
   (a VMM, or an AST2600 / AST2700 guest).  [this series]

3. ASPEED vHub, as a longer-term goal towards BMC KVM / Virtual Media
   support in QEMU.  [future]

This series implements goal 2.

The transport
=============

usb-redir-server exports a locally emulated USB device to a remote USB
host over the usbredir protocol, so a device emulated in one QEMU instance
can be enumerated by a host controller emulated in another one.

The left column is a request going to the device. The right column is the
answer coming back. The middle hop carries usbredir messages over a
socket. The top and bottom hops carry USBPackets inside QEMU.

    remote QEMU: guest driver -> EHCI/XHCI
             |                     ^
   USBPacket |                     | USBPacket
             v                     |
    "usb-redir" (the client)
             |                     ^
    usbredir |   chardev socket    | usbredir
             v                     |
    usb-redir-server (the server, this series)
             |                     ^
   USBPacket |                     | USBPacket
             v                     |
    any USBDevice, "-device <dev>,bus=<id>.0"

"usb-redir" (hw/usb/redirect.c) is the client:
  - it takes a USBPacket from the remote guest and writes it to the socket
    as a usbredir message
  - it reads the answer from the socket and completes the USBPacket

usb-redir-server is the server. It does the same thing, but backwards:
  - it reads a usbredir message from the socket and runs it as a USBPacket
    on the bus below
  - it takes the result of that USBPacket and writes it back to the same
    socket as a usbredir message, for the client to read

A USB device has to sit on a USB bus, and in QEMU a USB bus is always made
by a host controller. So usb-redir-server makes one and acts as the host
controller on this side. It models no real chip: its cable is the chardev
socket. The real host is in the other QEMU.

usbredir carries one device, not a bus. A hub cannot be exported: the
protocol has no device address field. To export several devices, run one
usb-redir-server per device, each with its own chardev.

Testing
=======
A plain usb-storage device was used to test the transport. The storage
device is attached to usb-redir-server and exported over a Unix socket:

$ qemu-system-aarch64 ...
-chardev socket,id=usbredir0,path=/tmp/usbredir0.sock,server=on,wait=off
-device usb-redir-server,id=usbredir0,chardev=usbredir0
-drive id=usbdisk,if=none,file=image0.ext4,format=raw
-device usb-storage,bus=usbredir0.0,id=mystorage,drive=usbdisk

The exported device can then be attached to EHCI bus 3 of an AST2700
guest using the existing usb-redir client:

    -chardev socket,id=storage,path=/tmp/usbredir0.sock,reconnect-ms=1000 \
    -device usb-redir,chardev=storage,bus=usb-bus.3

The AST2700 Linux guest enumerates the redirected USB storage device:

root@ast2700-default:~# lsusb
unable to initialize usb spec
Bus 001 Device 001: ID 1d6b:0001 Linux 6.18.36-v00.08.03-gaf2f426c5786 uhci_hcd Generic UHCI Host Controller
Bus 002 Device 001: ID 1d6b:0002 Linux 6.18.36-v00.08.03-gaf2f426c5786 ehci_hcd EHCI Host Controller
Bus 002 Device 002: ID 46f4:0001 QEMU QEMU USB HARDDRIVE

This also demonstrates that usb-redir-server is not specific to the
ASPEED UDC. Any USBDevice can be attached to its USB bus and exported
to a host controller in another QEMU instance.

v1:
  1. Add a usbredir server device
  2. Announce the exported device
  3. Implement control transfers
  4. Implement bulk and interrupt transfers
  5. Stream interrupt IN endpoints 

v2:
  1. Split the original series into USB and ASPEED parts as suggested
     during review.
  2. Keep this series focused on the usbredir server transport.
  3. Move the ASPEED UDC changes, AST1030 UDC support and its functional
     test to a separate series.

Jamin Lin (8):
  hw/usb/bus: Let a bus opt out of automatic hub insertion
  hw/usb/redirect-server: Add a usbredir server device
  hw/usb/redirect-server: Connect usbredirparser to a chardev
  hw/usb/redirect-server: Announce the exported device
  hw/usb/redirect-server: Implement control transfers
  hw/usb/redirect-server: Implement bulk and interrupt transfers
  hw/usb/redirect-server: Stream interrupt IN endpoints
  hw/arm/aspeed: Enable the usbredir server transport

 include/hw/usb/redirect-server.h |  116 +++
 include/hw/usb/usb.h             |    1 +
 hw/arm/aspeed.c                  |    6 +
 hw/usb/bus.c                     |    3 +-
 hw/usb/redirect-server.c         | 1604 ++++++++++++++++++++++++++++++
 hw/usb/meson.build               |    3 +-
 hw/usb/trace-events              |   27 +
 7 files changed, 1758 insertions(+), 2 deletions(-)
 create mode 100644 include/hw/usb/redirect-server.h
 create mode 100644 hw/usb/redirect-server.c

-- 
2.43.0