linux-2.6.36内核
start arch/arm/boot/compressed/head.S
arch/arm/kernel/head.S
start_kernel() init/main.c
linux通用内核启动代码在init/main.c中：
汇编执行完后跳转到start_kernel()开始C 执行。
...
setup_arch(&command_line); //把.config中配置的CONFIG_CMDLINE赋予command_line输出
...
setup_command_line(command_line); //boot_command_line =>save_command_line;
//command_line =>static_command_line;
...
printk(KERN_NOTICE ''kernel command line:%s ", boot_command_line);
...
console_init(）；
...
rest_init(); //创建两线程kernel_init /kthreadd
|----------->kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
|----------->kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES); //kernel/kthread.c
pid_t kernel_thread(int (*fn)(void *), void *args, unsigned long flags); //arch/arm/kernel/process.c
----------------------------------------------------------------------------------------------------------------------------------------
kernel_init() //init/main.c
|---------->do_basic_setup() //解压了相关文件系统
sys_open("/dev/console", O_RDWR, 0) <0
printk(KERN_WARNING "Warning: unable to open an initial console. ");
if(! ramdisk_execute_command)
ramdisk_execute_command = "/init"; //initramfs 默认启动进程衔接
if(sys_access(ramdisk_execute_command, 0) != 0){
ramdisk_execute_command = NULL;
prepare_namespace(); //处理除ramdisk和initramfs外的其他文件系统。
}
|---------->init_post();
// ramdisk_execute_command <= "rdinit="
// execute_command <= "init=" //bootargs传递
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kernel_init()-->do_basic_setup()
mm/CPU已运行，没有设备被创建。
786 /*
787 * Ok, the machine is now initialized. None of the devices
788 * have been touched yet, but the CPU subsystem is up and
789 * running, and memory and process management works.
790 *
791 * Now we can finally start doing some real work..
792 */
793 static void __init do_basic_setup(void)
794 {
795 cpuset_init_smp();
796 usermodehelper_init();
797 init_tmpfs();
798 driver_init();
799 init_irq_proc();
800 do_ctors();
801 do_initcalls();
802 }
773 extern initcall_t __initcall_start[], __initcall_end[], __early_initcall_end [];
774
775 static void __init do_initcalls(void)
776 {
777 initcall_t *fn;
778
779 for (fn = __early_initcall_end; fn < __initcall_end; fn++)
780 do_one_initcall(*fn);
781
782 /* Make sure there is no pending stuff from the initcall sequence */
783 flush_scheduled_work();
784 }
kernel_init() -> do_basic_setup() -> do_initcalls() ->rootfs_initcall(populate_rootfs) -> populate_rootfs()
ramdisk或initramfs的处理都是通过populate_rootfs()实现，位于init/initramfs.c中。
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init_post() // init/main.c
if (ramdisk_execute_command) {
835 run_init_process(ramdisk_execute_command);
836 printk(KERN_WARNING "Failed to execute %s
",
837 ramdisk_execute_command);
838 }
839
840 /*
841 * We try each of these until one succeeds.
842 *
843 * The Bourne shell can be used instead of init if we are
844 * trying to recover a really broken machine.
845 */
846 if (execute_command) {
847 run_init_process(execute_command);
848 printk(KERN_WARNING "Failed to execute %s. Attempting "
849 "defaults...
", execute_command);
850 }
851 run_init_process("/sbin/init");
852 run_init_process("/etc/init");
853 run_init_process("/bin/init");
854 run_init_process("/bin/sh");
855
856 panic("No init found. Try passing init= option to kernel. "
857 "See Linux Documentation/init.txt for guidance.");
linux系统启动完成后，任务都交给init进程完成。
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ramdisk和initramfs都是通过populate_rootfs()实现；
jffs,yaffs等通过prepare_namespace()实现，在do_mounts.c中。