linux-kernel-architecture

name	linux-kernel-architecture
description	Linux kernel architecture skill for subsystem overview. Use when navigating kernel source, understanding boot flow, initcalls, or major subsystems (VFS, scheduler, MM). Activates on queries about kernel architecture, boot process, initcall levels, subsystem layout, or where code lives in linux.git.

Linux Kernel Architecture

Purpose

Provide a mental map of the Linux kernel: boot sequence, major subsystems, key data structures, and where to look in source — complementing skills/kernel/kernel-internals with architecture-level navigation for driver and subsystem work.

When to Use

• First time exploring linux.git for a feature or bug
• Understanding how boot reaches init and driver probe
• Tracing a syscall or interrupt through subsystems
• Onboarding before skills/kernel-dev/platform-device-model or driver skills

Workflow

1. Boot flow (x86/ARM64 simplified)

firmware/UEFI
├── arch/*/boot — decompress kernel, early setup
├── start_kernel() — mm, scheduler, timers, IRQ subsys
├── rest_init() → kernel_init → run_init_process
└── userspace init (systemd)

Driver module_init / device_initcall run during start_kernel before init.

2. Major subsystems

Subsystem	Path (typical)	Key structs
Scheduler	kernel/sched/	task_struct, sched_entity
Memory	mm/	struct page, mm_struct, vm_area_struct
VFS	fs/	inode, dentry, file, super_block
Block	block/	request_queue, gendisk
Net	net/	sk_buff, net_device
Drivers	drivers/	device, device_driver
Syscalls	kernel/, fs/, mm/	SYSCALL_DEFINE*

3. Initcall levels

/* include/linux/init.h — order matters */
early_initcall → core_initcall → postcore_initcall
→ arch_initcall → subsys_initcall → fs_initcall
→ device_initcall → late_initcall

Platform drivers usually register at subsys_initcall or via module_init.

4. Finding code

# Locate symbol
grep -rn "platform_driver_register" drivers/

# Trace config
./scripts/config --state CONFIG_FOO

# File hierarchy docs
ls Documentation/admin-guide/

5. Agent usage

/linux-kernel-architecture Where does page fault handling live and what calls it?

Common Problems

Symptom	Cause	Fix
Driver probes too early	Initcall vs DT ordering	Defer with deferred_probe
Symbol missing	Built as module	modprobe or built-in CONFIG_*
Wrong subsystem	Similar names in drivers/	Follow struct bus_type
Boot hang	Early printk disabled	earlyprintk, initcall_debug

Related Skills

• skills/kernel/kernel-internals — scheduler, SLUB, VFS depth
• skills/kernel-dev/kernel-memory-management — mm/ details
• skills/kernel-dev/platform-device-model — driver model
• skills/kernel-dev/device-tree — hardware description
• skills/low-level-programming/linux-kernel-modules — LKM basics