netdevsim DKMS Driver

Out-of-tree DKMS package for the enhanced netdevsim kernel module with fake PCI device simulation, DPLL/GNSS emulation, PTP EXTTS support, and logical clock ID sharing.

Based on Linux 6.9.5 kernel sources.

Modules Included

Module	Description
netdevsim.ko	Enhanced netdevsim with fake PCI, DPLL, ethtool, logical clock IDs
nsim_ptp_mock.ko	Mock PTP clock with kref lifecycle, 2-pin layout, EXTTS simulation
nsim_ptp.ko	PTP core with nsim_ptp_class export and get_ptp_clock_info() helper
nsim_dpll.ko	DPLL subsystem with genlmsg_multicast_allns for cross-namespace events

Note: Modules are renamed from the upstream names (ptp → nsim_ptp, dpll → nsim_dpll, ptp_mock → nsim_ptp_mock) to avoid symbol conflicts with the kernel's built-in PTP and DPLL subsystems.

Kernel Compatibility

This package targets Linux 6.9.x kernels. Internal kernel APIs (devlink, dpll, netdevice, PTP) may differ in other kernel versions. Building against a substantially different kernel version will likely require source modifications.

Prerequisites

• dkms package installed
• Kernel headers for the target kernel (linux-headers-$(uname -r))

Installation

Using DKMS (recommended)

# Copy source tree to the DKMS source directory
sudo cp -r . /usr/src/netdevsim-6.9.5

# Register and build
sudo dkms add netdevsim/6.9.5
sudo dkms build netdevsim/6.9.5
sudo dkms install netdevsim/6.9.5

Manual build (without DKMS)

make
sudo make modules_install

Uninstallation

sudo dkms remove netdevsim/6.9.5 --all
sudo rm -rf /usr/src/netdevsim-6.9.5

Loading the modules

Load the modules in dependency order:

sudo modprobe nsim_ptp
sudo modprobe nsim_dpll
sudo modprobe netdevsim pci_bus_nr=0x1f

udev Rule

Install the udev rule to create /dev/ptp* compat device nodes:

sudo cp 99-nsim-ptp.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules

The nsim_ptp module registers a separate device class (/dev/nsim_ptp*) to avoid colliding with the kernel's built-in PTP subsystem. The udev rule creates real /dev/ptpN device nodes (via mknod, same major:minor) so that ethtool -T PHC indices resolve correctly for ptp4l and other linuxptp tools. Real device nodes propagate into containers, unlike symlinks which only exist on the host devtmpfs.

Usage

Create netdevsim devices via the bus interface:

# Format: "id pci_addr clk_id [num_ports]"
echo "1 0000:1f:02.0 1 2" | sudo tee /sys/bus/netdevsim/new_device

The pci_bus_nr module parameter controls the fake PCI host bridge bus:

sudo modprobe netdevsim pci_bus_nr=0x1f

Link two netdevsim interfaces as peers (required for packet forwarding):

exec 3< /proc/self/ns/net
IF0_IDX=$(cat /sys/class/net/eth0/ifindex)
IF1_IDX=$(cat /sys/class/net/eth1/ifindex)
echo "3:${IF0_IDX} 3:${IF1_IDX}" > /sys/bus/netdevsim/link_device
exec 3<&-

Container / Kubernetes Notes

When using netdevsim inside containers or Kubernetes pods:

• Device permissions: The nsim_ptp char devices use a non-standard major number (234) that may be blocked by cgroup device allowlists. The udev rule sets MODE="0666" to work around this. If devices were created before the rule was installed, run chmod 666 /dev/nsim_ptp*.

• Systemd services: Services with DevicePolicy=closed only allow char-ptp class devices. Override with a drop-in: DeviceAllow=char-* rw and DevicePolicy=auto.

• Kubernetes pods: The udev rule creates real /dev/ptpN device nodes (not symlinks) so they propagate into containers.

Local UTM VMs (macOS)

Prerequisites

1. Install UTM from https://mac.getutm.app or brew install --cask utm.
2. Symlink utmctl so it's on your PATH:

sudo ln -sf /Applications/UTM.app/Contents/MacOS/utmctl /usr/local/bin/utmctl

Quick Setup (no tests)

scripts/setup-utm-ubuntu.sh creates a UTM VM with the DKMS modules installed and loaded, adds an SSH config entry, and stops — no tests are run.

# Default: Ubuntu 24.04, DKMS installed, SSH config added
./scripts/setup-utm-ubuntu.sh

# Then connect:
ssh netdevsim-ubuntu-test

# Ubuntu 22.04 with a custom VM name
./scripts/setup-utm-ubuntu.sh --release 22.04 --vm-name my-dev-vm
ssh my-dev-vm

# Drop into a shell immediately after setup
./scripts/setup-utm-ubuntu.sh --shell

# Tear down VM and remove the SSH config entry
./scripts/setup-utm-ubuntu.sh --vm-name my-dev-vm --cleanup

If an SSH config entry for the VM name already exists, the script prompts you to remove it or pick a different --vm-name.

Testing

scripts/test-utm-ubuntu.sh does the same VM setup plus smoke tests and (optionally) the full ptp-operator test suite.

# Ubuntu 22.04 (kernel 6.8 HWE) — smoke tests only
./scripts/test-utm-ubuntu.sh --release 22.04 --skip-ptp-operator --shell

# Ubuntu 24.04 (kernel 6.17 HWE) — smoke tests only
./scripts/test-utm-ubuntu.sh --release 24.04 --skip-ptp-operator --shell

The --shell flag drops you into an SSH session after the tests pass. Use --skip-ptp-operator to only run the DKMS build and smoke tests.

Managing the VM

utmctl list                              # list VMs
utmctl ip-address netdevsim-ubuntu-test  # get VM IP
utmctl stop netdevsim-ubuntu-test        # stop VM
utmctl delete netdevsim-ubuntu-test      # delete VM

License

GPL-2.0