Adding Additional Emulation Drivers

Relevant source files

The following files were used as context for generating this wiki page:

• config.addendum.txt
• build-buggy-linux-7_0.bash
• README.md
• empty.go
• cmdline.txt

The gokrazy-kernel-buggy-linux-7_0 package provides a Linux 7.0 amd64 kernel specifically tailored for Tailscale natlab/vmtest environments. This kernel intentionally preserves a UDP GSO regression to facilitate mitigation testing in virtualized environments, such as QEMU q35 instances.

Adding additional emulation drivers involves modifying the kernel configuration addendum and rebuilding the kernel image. The kernel must include specific drivers for PCI, virtio block devices, and network interfaces to operate correctly within these emulated testbeds.

Sources: README.md:1-12, empty.go:5-9

Driver Configuration Architecture

Drivers are managed through a configuration addendum file that supplements the default Linux kernel configuration. The project uses a specific set of flags to enable support for virtualized hardware components frequently used in testing.

Supported Emulation Components

The kernel configuration prioritizes drivers required for stable execution under QEMU and similar hypervisors.

Component	Driver/Flag	Purpose
Virtio Storage	CONFIG_VIRTIO_BLK	Enables block device support for virtual disks.
Virtio Networking	CONFIG_VIRTIO_NET	Provides high-performance virtual networking.
Intel Network	CONFIG_IGB	Supports emulated Intel igb NICs for UDP GSO testing.
Random Number Gen	HW_RANDOM_VIRTIO	Provides entropy from the host to the guest.
Framebuffer	CONFIG_FB_SIMPLE	Enables basic display output for the console.

Sources: config.addendum.txt:19-24, config.addendum.txt:69-83, README.md:12-16

Configuration Data Flow

The following diagram illustrates how driver configurations are merged into the final kernel build process.

This diagram shows the sequence where the project-specific driver requirements are injected into the standard kernel configuration workflow.

Sources: build-buggy-linux-7_0.bash:17-21

Adding New Drivers

To add a new emulation driver, you must append the corresponding CONFIG_* symbol to the addendum file and execute the build script.

Driver Addition Procedure

1. Identify the required kernel configuration symbols for the driver.
2. Add the symbols to config.addendum.txt using the format CONFIG_DRIVER_NAME=y.
3. Run the build script: ./build-buggy-linux-7_0.bash.
4. Verify the resulting vmlinuz binary contains the new driver support.

Sources: build-buggy-linux-7_0.bash:20-25, config.addendum.txt:1-5

Network and Infrastructure Drivers

The kernel includes advanced networking support necessary for container-like plumbing and diagnostic testing.

• Virtio Infrastructure: Supports CONFIG_VIRTIO_PCI and CONFIG_VIRTIO_MMIO for various virtual bus types.
• Networking Tests: Includes CONFIG_BRIDGE and CONFIG_VETH for bridge/veth-based networking tests.
• Security/Firewall: Enables CONFIG_NF_TABLES (nftables) and CONFIG_BPF_SYSCALL for sophisticated network filtering.

Sources: config.addendum.txt:30-65, config.addendum.txt:75-76, config.addendum.txt:86-87

Implementation Details

The build system automates the retrieval and patching of the kernel source.

The script ensures that the config.addendum.txt is always applied after the default configuration to override or add specific emulation drivers.

Sources: build-buggy-linux-7_0.bash:7-22

Boot Requirements

The kernel requires specific command-line parameters to identify the root filesystem and initialization process.

root=/dev/sda2 ro init=/gokrazy/init panic=10 oops=panic

This configuration ensures the kernel uses the second partition of the first SCSI/SATA/Virtio-Block device as the root, which is standard for gokrazy deployments.

Sources: cmdline.txt:1