kfragments

Modular kernel configuration fragments for building custom Linux kernels targeting QEMU/KVM virtual machines. Feature fragments default to =m for tristate configs. A builtin/ subdirectory provides =y overrides for boot scenarios without module loading.

Fragment naming and comment style follow the upstream kernel convention (kernel/configs/ in the Linux source tree). Fragments are grouped by topic into topical subdirectories under kernel/configs/:

core/       base kernel, modules, init system, boot, firmware, hardening
arch/       per-architecture (x86_64 / arm64) knobs and extras
fs/         filesystems
storage/    block layer, device mapper, MD, NVMe, NVDIMM, CXL
virt/       virtio device drivers, KVM host
net/        iptables, nftables, Docker/Moby
security/   LSMs, IMA/EVM, crypto API and algorithms
mem/        memory-management knobs (DAMON, KSM, NUMA, zswap)
debug/      developer instrumentation and sanitizers
test/       in-tree test infrastructure
rust/       Rust language and module-versioning
perf/       performance monitoring

builtin/ mirrors the same subdirectory layout: builtin/fs/ext4.config is the =y override for fs/ext4.config.

How to use it

Run merge_config.sh from the kernel source tree and pass the fragments you want. $C is the path to this project's kernel/configs/ directory.

A minimal bootable x86_64 VM with ext4 root and virtio-net:

./scripts/kconfig/merge_config.sh -n -O ../build \
    ../build/.config \
    $C/core/64bit.config \
    $C/core/modules.config \
    $C/core/core.config \
    $C/core/systemd.config \
    $C/core/initrd.config \
    $C/arch/x86_64.config \
    $C/core/acpi-poweroff.config \
    $C/fs/ext4.config \
    $C/virt/virtio-net.config \
    $C/core/localversion.config

Append any other feature fragment to add it. To build a feature into the kernel instead of as a module, add -y to the command line and append the matching builtin/ fragment. -y ("make builtin have precedence over modules") stops a =m from demoting the builtin/ =y value, so fragment order does not matter:

./scripts/kconfig/merge_config.sh -y -n -O ../build \
    ../build/.config \
    ... \
    $C/fs/ext4.config \
    $C/virt/virtio-fs.config \
    $C/builtin/fs/ext4.config \
    $C/builtin/virt/virtio-fs.config

Each builtin fragment is self-contained: it sets the target symbol and every tristate dependency to =y (for example builtin/virt/virtio-fs pulls in VIRTIO=y and VIRTIO_PCI=y). -y only protects a =y that a fragment already supplies; it does not by itself promote a feature fragment's =m to =y, which is why the matching builtin/ fragment still has to be on the line.

See docs/design-decisions.md for the full design: why =m is the default, how the builtin/ override model works, the Kconfig exceptions that force specific symbols to =y, and the list of configs this project deliberately omits.

Everything built-in (no modules)

For a kernel that runs without a module loader at all, just drop core/modules.config from the merge. With CONFIG_MODULES=n the kernel has no module state, so make olddefconfig promotes every =m to =y on its own; no builtin/ fragments are needed and -y has nothing to do:

./scripts/kconfig/merge_config.sh -n -O ../build \
    ../build/.config \
    $C/core/64bit.config \
    $C/core/core.config \
    $C/core/systemd.config \
    $C/core/initrd.config \
    $C/arch/x86_64.config \
    $C/core/acpi-poweroff.config \
    $C/fs/ext4.config \
    $C/virt/virtio-net.config \
    $C/core/localversion.config

After make olddefconfig, the final .config contains # CONFIG_MODULES is not set and zero =m lines; every enabled tristate is =y. This is the right shape for a no-module-loader boot (custom init, initramfs-less boot, or a recovery kernel where modprobe is not available).

Verifying a merged .config

scripts/verify_config.sh checks that the values you requested in the fragments actually appear in the final .config. It handles the last-wins rule and prints a summary of =y/=m totals. Pass -k the kernel tree, <linux> below; docs/verification.md explains why.

scripts/verify_config.sh -k <linux> ../build/.config \
    $C/core/64bit.config $C/core/modules.config $C/core/core.config \
    $C/core/systemd.config $C/core/initrd.config $C/arch/x86_64.config \
    $C/core/acpi-poweroff.config $C/fs/ext4.config \
    $C/virt/virtio-net.config $C/core/localversion.config

License

This project is licensed under copyleft-next-0.3.1. See LICENSE and COPYING for details.