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Inside init/main.c:kernel_init(): 854 855 static int __init kernel_init(void * unused) 856 { 857 lock_kernel(); 858 859 /* 860 * init can allocate pages on any node 861 */ 862 set_mems_allowed(node_possible_map); 863 /* 864 * init can run on any cpu. 865 */ 866 set_cpus_allowed_ptr(current, cpu_all_mask); 867 /* 868 * Tell the world that we're going to be the grim 869 * reaper of innocent orphaned children. 870 * 871 * We don't want people to have to make incorrect 872 * assumptions about where in the task array this 873 * can be found. 874 */ 875 init_pid_ns.child_reaper = current; 876 877 cad_pid = task_pid(current); 878 879 smp_prepare_cpus(setup_max_cpus); 880 881 do_pre_smp_initcalls(); 882 start_boot_trace(); 883 884 smp_init(); 885 sched_init_smp(); 886 887 do_basic_setup(); 888 901 902 /* 903 * Ok, we have completed the initial bootup, and 904 * we're essentially up and running. Get rid of the 905 * initmem segments and start the user-mode stuff.. 906 */ 907 908 init_post(); 909 return 0; 910 } here do_basic_setup() (above) is executed: 775 /* 776 * Ok, the machine is now initialized. None of the devices 777 * have been touched yet, but the CPU subsystem is up and 778 * running, and memory and process management works. 779 * 780 * Now we can finally start doing some real work.. 781 */ 782 static void __init do_basic_setup(void) 783 { 784 rcu_init_sched(); /* needed by module_init stage. */ 785 init_workqueues(); 786 cpuset_init_smp(); 787 usermodehelper_init(); 788 driver_init(); 789 init_irq_proc(); 790 do_ctors(); 791 do_initcalls(); 792 } 793 >From above, we can see do_initcalls() is executed: 764 static void __init do_initcalls(void) 765 { 766 initcall_t *call; 767 768 for (call = __early_initcall_end; call < __initcall_end; call++) 769 do_one_initcall(*call); 770 771 /* Make sure there is no pending stuff from the initcall sequence */ 772 flush_scheduled_work(); 773 } and among the initcalls to be made is populate_rootfs(): 567 568 static int __init populate_rootfs(void) 569 { 570 char *err = unpack_to_rootfs(__initramfs_start, 571 __initramfs_end - __initramfs_start); 572 if (err) 573 panic(err); /* Failed to decompress INTERNAL initramfs */ 574 if (initrd_start) { 575 #ifdef CONFIG_BLK_DEV_RAM 576 int fd; 577 printk(KERN_INFO "Trying to unpack rootfs image as initramfs...\n"); 578 err = unpack_to_rootfs((char *)initrd_start, 579 initrd_end - initrd_start); 580 if (!err) { 581 free_initrd(); 582 return 0; 583 } else { 584 clean_rootfs(); 585 unpack_to_rootfs(__initramfs_start, 586 __initramfs_end - __initramfs_start); 587 } 588 printk(KERN_INFO "rootfs image is not initramfs (%s)" 589 "; looks like an initrd\n", err); 590 fd = sys_open("/initrd.image", O_WRONLY|O_CREAT, 0700); 591 if (fd >= 0) { 592 sys_write(fd, (char *)initrd_start, 593 initrd_end - initrd_start); 594 sys_close(fd); 595 free_initrd(); 596 } 597 #else 598 printk(KERN_INFO "Unpacking initramfs...\n"); 599 err = unpack_to_rootfs((char *)initrd_start, 600 initrd_end - initrd_start); 601 if (err) 602 printk(KERN_EMERG "Initramfs unpacking failed: %s\n", err); 603 free_initrd(); 604 #endif 605 } 606 return 0; 607 } 608 rootfs_initcall(populate_rootfs); Here the rootfs is setup, and torn down later (except retain_initrd being specified). And note that after all the do_basic_setup() is the init_post(): 901 902 /* 903 * Ok, we have completed the initial bootup, and 904 * we're essentially up and running. Get rid of the 905 * initmem segments and start the user-mode stuff.. 906 */ 907 908 init_post(); 909 return 0; 910 } where all the userspace scripts are executed: 836 /* 837 * We try each of these until one succeeds. 838 * 839 * The Bourne shell can be used instead of init if we are 840 * trying to recover a really broken machine. 841 */ 842 if (execute_command) { 843 run_init_process(execute_command); 844 printk(KERN_WARNING "Failed to execute %s. Attempting " 845 "defaults...\n", execute_command); 846 } 847 run_init_process("/sbin/init"); 848 run_init_process("/etc/init"); 849 run_init_process("/bin/init"); 850 run_init_process("/bin/sh"); 851 852 panic("No init found. Try passing init= option to kernel."); 853 } Who call kernel_init()? Arch-specific start_kernel()=====>rest_init()====>kernel_init(). 667 #endif 668 thread_info_cache_init(); 669 cred_init(); 670 fork_init(num_physpages); 671 proc_caches_init(); 672 buffer_init(); 673 key_init(); 674 security_init(); 675 vfs_caches_init(num_physpages); 676 radix_tree_init(); 677 signals_init(); 678 /* rootfs populating might need page-writeback */ 679 page_writeback_init(); 680 #ifdef CONFIG_PROC_FS 681 proc_root_init(); 682 #endif 683 cgroup_init(); 684 cpuset_init(); 685 taskstats_init_early(); 686 delayacct_init(); 687 688 check_bugs(); 689 690 acpi_early_init(); /* before LAPIC and SMP init */ 691 692 ftrace_init(); 693 694 /* Do the rest non-__init'ed, we're now alive */ 695 rest_init(); 696 } 697 and kernel thread start kernel_init(): 425 static noinline void __init_refok rest_init(void) 426 __releases(kernel_lock) 427 { 428 int pid; 429 430 rcu_scheduler_starting(); 431 kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND); 432 numa_default_policy(); 433 pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES); 434 kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns); 435 unlock_kernel(); 436 |
