Networking with QEMU¶

This page describes how to set up a “virtual” networking between a (Linux) host and a Zephyr application running in a QEMU virtual machine (built for Zephyr targets like qemu_x86, qemu_cortex_m3, etc.) In this example, the echo_server sample application from Zephyr source distribution is run in QEMU. The QEMU instance is connected to Linux host using serial port and SLIP is used to transfer data between Zephyr and Linux (over a chain of virtual connections).

Prerequisites¶

On the Linux Host you need to fetch Zephyr net-tools project, which is located in a separate git repository:

$ git clone https://github.com/zephyrproject-rtos/net-tools
$ cd net-tools
$ make

Note

If you get error about AX_CHECK_COMPILE_FLAG, install package autoconf-archive package on Debian/Ubuntu.

Basic Setup¶

For the steps below, you will need at least 4 terminal windows:

Terminal #1 is your usual Zephyr development terminal, with Zephyr environment initialized.
Terminals #2, #3, #4 - fresh terminal windows with net-tools being the current directory (“cd net-tools”)

Step 1 - Create helper socket¶

Before starting QEMU with network emulation, a Unix socket for the emulation should be created.

In terminal #2, type:

$ ./loop-socat.sh

Step 2 - Start TAP device routing daemon¶

In terminal #3, type:

$ sudo ./loop-slip-tap.sh

Step 3 - Start app in QEMU¶

Build and start the echo_server sample application.

In terminal #1, type:

$ cd $ZEPHYR_BASE/samples/net/echo_server
$ mkdir build && cd build
$ cmake -DBOARD=qemu_x86 ..
$ make run

If you see error from QEMU about unix:/tmp/slip.sock, it means you missed Step 1 above.

Step 4 - Run apps on host¶

Now in terminal #4, you can run various tools to communicate with the application running in QEMU.

You can start with pings:

$ ping 192.0.2.1
$ ping6 2001:db8::1

For example, using netcat (“nc”) utility, connecting using UDP:

$ echo foobar | nc -6 -u 2001:db8::1 4242
foobar

$ echo foobar | nc -u 192.0.2.1 4242
foobar

If echo_server is compiled with TCP support (now enabled by default for echo_server sample, CONFIG_NET_TCP=y):

$ echo foobar | nc -6 -q2 2001:db8::1 4242
foobar

Note

You will need to Ctrl+C manually.

You can also use the telnet command to achieve the above.

Step 5 - Stop supporting daemons¶

When you are finished with network testing using QEMU, you should stop any daemons or helpers started in the initial steps, to avoid possible networking or routing problems such as address conflicts in local network interfaces. For example, you definitely need to stop them if you switch from testing networking with QEMU to using real hardware. For example, there was a report of an airport WiFi connection not working during travel due to an address conflict.

To stop the daemons, just press Ctrl+C in the corresponding terminal windows (you need to stop both loop-slip-tap.sh and loop-socat.sh).

Setting up Zephyr and NAT/masquerading on QEMU host to access Internet¶

To access the Internet from a Zephyr application using IPv4, a gateway should be set via DHCP or configured manually. For applications using the Network Application API facility (with the config option CONFIG_NET_APP enabled), set the CONFIG_NET_APP_MY_IPV4_GW option to the IP address of the gateway. For apps not using the Network Application API facility, set up the gateway by calling the net_if_ipv4_set_gw() at runtime.

To access Internet from a custom application running in a QEMU, NAT (masquerading) should be set up for QEMU’s source address. Assuming 192.0.2.1 is used, the following command should be run as root:

$ iptables -t nat -A POSTROUTING -j MASQUERADE -s 192.0.2.1

Additionally, IPv4 forwarding should be enabled on host, and you may need to check that other firewall (iptables) rules don’t interfere with masquerading.

Network connection between two QEMU VMs¶

Unlike VM-Host setup described above, VM-VM setup is automatic - for sample applications which support such mode such as the echo_server and echo_client samples, you will need 2 terminal windows, set up for Zephyr development.

Terminal #1:¶

$ cd $ZEPHYR_BASE/samples/net/echo_server
$ mkdir build && cd build
$ cmake -DBOARD=qemu_x86 ..
$ make server

This will start QEMU, waiting for connection from a client QEMU.

Terminal #2:¶

$ cd $ZEPHYR_BASE/samples/net/echo_client
$ mkdir build && cd build
$ cmake -DBOARD=qemu_x86 ..
$ make client

This will start 2nd QEMU instance, and you should see logging of data sent and received in both.

Running multiple QEMU VMs of the same sample¶

If you find yourself needing to run multiple instances of the same Zephyr sample application, which do not need to be able to talk to each other, the QEMU_INSTANCE argument is what you need.

Start socat and tunslip6 manually (avoiding loop-x.sh scripts) for as many instances as you want. Use the following as a guide, replacing MAIN or OTHER.

Terminal #1:¶

$ socat PTY,link=/tmp/slip.devMAIN UNIX-LISTEN:/tmp/slip.sockMAIN
$ $ZEPHYR_BASE/../net-tools/tunslip6 -t tapMAIN -T -s /tmp/slip.devMAIN \
     2001:db8::1/64
# Now run Zephyr
$ make run QEMU_INSTANCE=MAIN

Terminal #2:¶

$ socat PTY,link=/tmp/slip.devOTHER UNIX-LISTEN:/tmp/slip.sockOTHER
$ $ZEPHYR_BASE/../net-tools/tunslip6 -t tapOTHER -T -s /tmp/slip.devOTHER \
     2001:db8::1/64
$ make run QEMU_INSTANCE=OTHER