Friday, May 9, 2008

Linux init ("ASCII art")

Linux init ("ASCII art")









Pictorially (loosely speaking :), Linux initialization looks like
this, where "[...]" means optional (depends on the kernel's
configuration) and "{...}" is a comment.











+-------------------------------+ | arch/i386/boot/setup.S:: + | | arch/i386/boot/video.S:: | |-------------------------------| | start_of_setup: | | check that loaded OK | | get system memory size | | get video mode(s) | | get hard disk parameters | | get MC bus information | | get mouse information | | get APM BIOS information | | enable address line A20 | | reset coprocessor | | mask all interrupts | | move to protected mode | | jmp to startup_32 | +-------------------------------+ | v +-------------------------------+ | arch/i386/kernel/head.S:: | |-------------------------------| | startup_32: | | set segment registers to | | known values | | init basic page tables | | setup the stack pointer | | clear kernel BSS | | setup the IDT | | checkCPUtype | | load GDT, IDT, and LDT | | pointer registers | | start_kernel | | {it does not return} | +-------------------------------+ | v +-------------------------------+ +-------------------------------+ | init/main.c:: | +->| arch/i386/kernel/setup.c:: | |-------------------------------| | |-------------------------------| | start_kernel(): | | | setup_arch(): | | lock_kernel | | | copy boot parameters | | setup_arch |--+ | init ramdisk | | parse_options |<-+ | setup_memory_region | | trap_init | | | parse_cmd_line | | cpu_init | | | use the BIOS memory map to | | init_IRQ | | | setup page frame info. | | sched_init | | | reserve physical page 0 | | init_timervecs | | | [find_smp_config] | | time_init | | | paging_init | | softirq_init | | | [get_smp_config] | | console_init | | | [init_apic_mappings] | | [init_modules] | | | [reserve INITRD memory] | | [profiling setup] | | | probe_roms to search | | kmem_cache_init | | | for option ROMs | | sti | | | request_resource to | | calibrate_delay | | | reserve video RAM memory | | [INITRD setup] | | | request_resource to | | mem_init | | | reserve all standard PC | | free_all_bootmem | +--| I/O system board resources| | kmem_cache_sizes_init | +-------------------------------+ | [proc_root_init] | | fork_init | | proc_caches_init | | vfs_caches_init | | buffer_init | | page_cache_init | | kiobuf_setup | | signals_init | +-------------------------------+ | bdev_init | | init/main.c:: | | inode_init | | init(): {...init thread...} | | [ipc_init] | | do_basic_setup | | [dquot_init_hash] | | {bus/dev init & initcalls}| | check_bugs | | free_initmem | | [smp_init] {*below} | | open /dev/console | | start init thread {---->} |.....| exec init script or shell | | unlock_kernel | | or panic | | cpu_idle | +-------------------------------+ +-------------------------------+ +-------------------------------+ | smpboot.c::smp_init | |-------------------------------| | arch/i386/kernel/smpboot.c:: | | smp_boot_cpus(): | | [mtrr_init_boot_cpu] | | smp_store_cpu_info | | print_cpu_info | | save CPU ID/APIC ID mappings| | verify_local_APIC | | connect_bsp_APIC | | setup_local_APIC | | foreach valid APIC ID | | do_boot_cpu(apicid) | | setup_IO_APIC | | setup_APIC_clocks | | synchronize_tsc_bp | +-------------------------------+
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