How to use USB device networking
The Linux USB gadget sub-system supports USB device functionality, including USB networking.
- 1 Configure hardware for USB OTG or USB device support
- 2 Build USB Ethernet network gadget driver
- 3 Load USB Ethernet network gadget driver
- 4 Connect device to host PC
- 5 Assigning IP addresses
- 6 Verifying network connectivity
- 7 Bridging host PC to allow device to reach the Internet
- 8 Configuring a DNS name server
- 9 Mounting NFS file system
- 10 Debugging and resolving common errors
Configure hardware for USB OTG or USB device support
Depending on your hardware, you can use either USB OTG or USB device to enable support for USB networking.
Build USB Ethernet network gadget driver
The USB Ethernet network gadget driver caused the device to appear to be a USB network dongle when connected to a host computer. Generally it is best to build USB gadget drivers as modules instead of building them into the kernel so you can unload one and load another.
Symbol: USB_ETH [=m] Prompt: Ethernet Gadget (with CDC Ethernet support) Defined at drivers/usb/gadget/Kconfig:628 Depends on: <choice> && NET Location: -> Kernel configuration -> Device Drivers -> USB support (USB_SUPPORT [=y]) -> USB Gadget Support (USB_GADGET [=y]) -> USB Gadget Drivers (<choice> [=m])
If you want the target to mount a host PC directory using NFS, then also enable NFS mount support in busybox:
Symbol: FEATURE_MOUNT_NFS [=n] Prompt: Support mounting NFS file systems Defined at util-linux/Config.in:549 Depends on: FS_APPS_BUSYBOX && MOUNT Location: -> File System Configuration -> Select target's file system software -> busybox-1.18.2 (FS_APPS_BUSYBOX [=y]) -> Busybox configuration -> Linux System Utilities -> mount (MOUNT [=y]) Selects: FEATURE_HAVE_RPC && FEATURE_SYSLOG
Build the SDK and install the new images to the target hardware.
Load USB Ethernet network gadget driver
After booting the target hardware to a shell prompt, run:
and you should see output similar to:
g_ether gadget: using random self ethernet address g_ether gadget: using random host ethernet address usb0: MAC be:b5:85:ef:48:33 usb0: HOST MAC 1a:b2:c3:43:8a:6e g_ether gadget: Ethernet Gadget, version: Memorial Day 2008 g_ether gadget: g_ether ready
You can then verify the usb0 network interface exists:
with output similar to:
usb0 Link encap:Ethernet HWaddr BE:B5:85:EF:48:33 BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Connect device to host PC
Before connecting the target device to the host PC, watch the syslog, by running the following command on the host PC:
sudo tail -f /var/log/messages
Connect the USB cable between the target device and the host PC. The messages file on the host PC should indicate the new USB device was detected.
Jun 6 10:15:29 contra-lx kernel: [1638241.377831] usb 1-4.4.2: new high speed USB device using ehci_hcd and address 47 Jun 6 10:15:29 contra-lx kernel: [1638241.510787] cdc_subset: probe of 1-4.4.2:1.0 failed with error -22 Jun 6 10:15:29 contra-lx kernel: [1638241.513437] cdc_subset 1-4.4.2:1.1: usb0: register 'cdc_subset' at usb-0000:00:02.1-4.4.2, Linux Device, 82:13:56:20:b4:cb Jun 6 10:15:29 contra-lx kernel: [1638241.513490] usbcore: registered new interface driver cdc_subset Jun 6 10:15:29 contra-lx kernel: [1638241.533442] cdc_ether: probe of 1-4.4.2:1.0 failed with error -16 Jun 6 10:15:29 contra-lx kernel: [1638241.533619] usbcore: registered new interface driver cdc_ether
On the host you can verify the new usb0 interface exists by running:
with the output being similar to:
usb0 Link encap:Ethernet HWaddr 82:13:56:20:b4:cb inet6 addr: fe80::8013:56ff:fe20:b4cb/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:1 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:78 (78.0 B)
When you connect the cable, in the target device console, you should see:
g_ether gadget: high speed config #1: CDC Ethernet (ECM)
Assigning IP addresses
For this simple example, fixed IP addresses are assigned to the both the host PC USB network interface and the target device USB network interface.
On the host
HOST_USB_IP=10.0.1.1 sudo ifconfig usb0 $HOST_USB_IP netmask 255.255.255.0 route
with an entry from the route output that looks like
Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 10.0.1.0 * 255.255.255.0 U 0 0 0 usb0 ... link-local * 255.255.0.0 U 1000 0 0 eth0 default gw 0.0.0.0 UG 100 0 0 eth0
On the target device
HOST_USB_IP=10.0.1.1 TARGET_USB_IP=10.0.1.2 ifconfig usb0 $TARGET_USB_IP netmask 255.255.255.0 route add default gw $HOST_USB_IP route
with the route showing the default gateway is using usb0
Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 10.0.1.0 * 255.255.255.0 U 0 0 0 usb0 default 10.0.1.1 0.0.0.0 UG 0 0 0 usb0
Verifying network connectivity
On the target device, ping the host PC:
ping -c 5 10.0.1.1
On the host PC, verify the number of packet sent and received is not zero
Look at the values of RX packets: and TX packets:.
Bridging host PC to allow device to reach the Internet
If your host PC is connected to the Internet (through WiFi or Ethernet), then you can allow the target device to share the host PC's Internet connection. The following shows how to enable, test, and disable. It only works if your host PC doesn't have a firewall enable. There is a lot of information on how the Internet giving more detailed explanation.
On the host PC:
echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward > /dev/null sudo iptables -P FORWARD ACCEPT sudo iptables -A POSTROUTING -t nat -j MASQUERADE -s 10.0.1.0/24
And then for reasons I don't fully undestand, I had to configure usb0 on the host again:
HOST_USB_IP=10.0.1.1 sudo ifconfig usb0 $HOST_USB_IP netmask 255.255.255.0 route
On the target device:
ping -c 5 126.96.36.199 # This is Google's domain name server
To disable forwarding network packets on your host PC:
echo 0 | sudo tee /proc/sys/net/ipv4/ip_forward > /dev/null sudo iptables -t nat -F POSTROUTING
Configuring a DNS name server
If you need to resolve DNS names, you can configure your target hardware to use Google's DNS server via:
echo "nameserver 188.8.131.52" >> /etc/resolv.conf
and you can test that names get resolved by pinging some computer on the Internet:
ping -c 5 google.com
Mounting NFS file system
If you have already enabled NFS share of your development directory target file system, $DEVDIR/fs/fs, then you can easily mount the file system on the target. This is different than a root NFS mount. With a root NFS mount, networking has to be available when the kernel is booting. With a normal (non root file system) NFS mount, you are simply mounting a shared directory somewhere in the target device's file system.
First verify you build the target file system kernel with NFS enabled:
fgrep nfs /proc/filesystems
with expected output
Mount host file system on target:
HOST_USB_IP=10.0.1.1 HOST_NFS_SHARE_DIR=/local/home/tfischer/work/sdk/fs/fs mkdir /tmp/nfs mount -t nfs $HOST_USB_IP:$HOST_NFS_SHARE_DIR /tmp/nfs
Debugging and resolving common errors
Wireshark is your friend. Run wireshark on your host PC monitoring the usb0 interface and you don't need any packet filters. If something isn't working, you will see the last packet that was sent and not responded to. That will give you a big hint as to where to start looking for the problem.
NFS mount failed reason given by server: Permission denied
If you see a message like
mount: 10.0.1.1:/local/home/tfischer/work/sdk/fs/fs failed, reason given by server: Permission denied mount: mounting 10.0.1.1:/local/home/tfischer/work/sdk/fs/fs on /tmp/nfs failed: Bad file descriptor
and you know you have root NFS working, the cause is due to a different sub-LAN address being used. On your host PC, you need to make sure the 10.0.1.* sub-LAN is exported. Run the following commands to export you home directory to all computers on this sub-LAN:
echo "$HOME 10.0.1.0/24 (rw,no_root_squash,no_subtree_check)" | sudo tee -a /etc/exports > /dev/null sudo exportfs