Using the mtty vfio-mdev sample code

mtty is a sample vfio-mdev driver that demonstrates how to use the mediated device framework.

The sample driver creates an mdev device that simulates a serial port over a PCI card.

Build and load the mtty.ko module.

This step creates a dummy device, /sys/devices/virtual/mtty/mtty/

Files in this device directory in sysfs are similar to the following:

# tree /sys/devices/virtual/mtty/mtty/
   /sys/devices/virtual/mtty/mtty/
   |-- mdev_supported_types
   |   |-- mtty-1
   |   |   |-- available_instances
   |   |   |-- create
   |   |   |-- device_api
   |   |   |-- devices
   |   |   `-- name
   |   `-- mtty-2
   |       |-- available_instances
   |       |-- create
   |       |-- device_api
   |       |-- devices
   |       `-- name
   |-- mtty_dev
   |   `-- sample_mtty_dev
   |-- power
   |   |-- autosuspend_delay_ms
   |   |-- control
   |   |-- runtime_active_time
   |   |-- runtime_status
   |   `-- runtime_suspended_time
   |-- subsystem -> ../../../../class/mtty
   `-- uevent

Create a mediated device by using the dummy device that you created in the previous step:

# echo "83b8f4f2-509f-382f-3c1e-e6bfe0fa1001" >    \
         /sys/devices/virtual/mtty/mtty/mdev_supported_types/mtty-2/create

Add parameters to qemu-kvm:

-device vfio-pci,\
 sysfsdev=/sys/bus/mdev/devices/83b8f4f2-509f-382f-3c1e-e6bfe0fa1001

Boot the VM.

In the Linux guest VM, with no hardware on the host, the device appears as follows:

# lspci -s 00:05.0 -xxvv
00:05.0 Serial controller: Device 4348:3253 (rev 10) (prog-if 02 [16550])
        Subsystem: Device 4348:3253
        Physical Slot: 5
        Control: I/O+ Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR- FastB2B- DisINTx-
        Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=medium >TAbort-
<TAbort- <MAbort- >SERR- <PERR- INTx-
        Interrupt: pin A routed to IRQ 10
        Region 0: I/O ports at c150 [size=8]
        Region 1: I/O ports at c158 [size=8]
        Kernel driver in use: serial
00: 48 43 53 32 01 00 00 02 10 02 00 07 00 00 00 00
10: 51 c1 00 00 59 c1 00 00 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 00 00 00 00 48 43 53 32
30: 00 00 00 00 00 00 00 00 00 00 00 00 0a 01 00 00

In the Linux guest VM, dmesg output for the device is as follows:

serial 0000:00:05.0: PCI INT A -> Link[LNKA] -> GSI 10 (level, high) -> IRQ 10
0000:00:05.0: ttyS1 at I/O 0xc150 (irq = 10) is a 16550A
0000:00:05.0: ttyS2 at I/O 0xc158 (irq = 10) is a 16550A

In the Linux guest VM, check the serial ports:

# setserial -g /dev/ttyS*
/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
/dev/ttyS1, UART: 16550A, Port: 0xc150, IRQ: 10
/dev/ttyS2, UART: 16550A, Port: 0xc158, IRQ: 10

Using minicom or any terminal emulation program, open port /dev/ttyS1 or /dev/ttyS2 with hardware flow control disabled.
Type data on the minicom terminal or send data to the terminal emulation program and read the data.

Data is loop backed from hosts mtty driver.

Destroy the mediated device that you created:

# echo 1 > /sys/bus/mdev/devices/83b8f4f2-509f-382f-3c1e-e6bfe0fa1001/remove

File	Mode	Size
Makefile	-rw-r--r--	234 bytes
README.rst	-rw-r--r--	3.4 KB
mbochs.c	-rw-r--r--	35.9 KB
mdpy-defs.h	-rw-r--r--	763 bytes
mdpy-fb.c	-rw-r--r--	5.4 KB
mdpy.c	-rw-r--r--	17.6 KB
mtty.c	-rw-r--r--	47.5 KB

README.rst