linux-kernel-architecture

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