kernel_init ============ 0号进程创建1号进程的方式如下 :: kernel_thread(kernel_init, NULL, CLONE_FS); 1号进程的执行函数就是 ``kernel_init`` ，这个函数定义在 ``init/main.c`` 中,代码实现如下 :: static int __ref kernel_init(void *unused) { int ret; kernel_init_freeable(); /* need to finish all async __init code before freeing the memory */ async_synchronize_full(); ftrace_free_init_mem(); free_initmem(); mark_readonly(); /* * Kernel mappings are now finalized - update the userspace page-table * to finalize PTI. */ pti_finalize(); system_state = SYSTEM_RUNNING; numa_default_policy(); rcu_end_inkernel_boot(); if (ramdisk_execute_command) { ret = run_init_process(ramdisk_execute_command); if (!ret) return 0; pr_err("Failed to execute %s (error %d)\n", ramdisk_execute_command, ret); } /* * We try each of these until one succeeds. * * The Bourne shell can be used instead of init if we are * trying to recover a really broken machine. */ if (execute_command) { ret = run_init_process(execute_command); if (!ret) return 0; panic("Requested init %s failed (error %d).", execute_command, ret); } if (!try_to_run_init_process("/sbin/init") || !try_to_run_init_process("/etc/init") || !try_to_run_init_process("/bin/init") || !try_to_run_init_process("/bin/sh")) return 0; panic("No working init found. Try passing init= option to kernel. " "See Linux Documentation/admin-guide/init.rst for guidance."); } kernel_init 函数执行内核的部分初始化工作,及系统配置,并创建若干个用于高速缓存和虚拟内存管理的内核线程 init进程 --------- 1号进程调用do_execve运行可执行程序init，并演变为用户态1号进程,即init进程。init进程有许多重要的任务,比如启动getty(用于用户登录)、实现运行级别、以及处理孤立进程 0号进程---->1号内核进程---->1号用户进程---->getty进程---->shell进程 内核会在几个位置来查询init,按优先级顺序依次为 1. /sbin/init 2. /etc/init 3./bin/init 4/bin/sh init程序是一个可以由用户编写的进程,以下是init的几个变种 +-------------------+------------------------------------------------------------------------------------------+ | init包 | 说明 | +===================+==========================================================================================+ | sysvinit | 早期使用的初始化进程工具,目前逐渐淡出linux的历史舞台 | +-------------------+------------------------------------------------------------------------------------------+ | upstart | debian,ubuntu等系统使用的init daemon | +-------------------+------------------------------------------------------------------------------------------+ | systemd | systemd是linux中最新的初始化系统(init),可以提高系统的启动速度 | +-------------------+------------------------------------------------------------------------------------------+ kerner_init分析 ---------------- +------------------------+-----------------------------------------------------------------------------------------------------------------------------+ | 执行流程 | 说明 | +========================+=============================================================================================================================+ | kernel_init_freeable | 完成初始化工作,准备文件系统,准备模块信息 | +------------------------+-----------------------------------------------------------------------------------------------------------------------------+ | async_synchronize_full | 用来加速linux kernel开机的效率 | | | | +------------------------+-----------------------------------------------------------------------------------------------------------------------------+ | free_initmem | free_initmem(in arch/arm/mm/init.c)释放kernel介于__init_begin到__init_end属于init Section的函数的所有内存,并把page个数加到 | | | tatolram_pages中,作为后续kernel在配置mem时可以使用的pages | | | | +------------------------+-----------------------------------------------------------------------------------------------------------------------------+ | system_state | 设置运行状态为SYSTEM_RUNNING | +------------------------+-----------------------------------------------------------------------------------------------------------------------------+ | | a.如果ramdisk_execute_command不为0就执行该命令为init user process | | | b.如果execute_command不为0，就行执行该命令称为init user process | | 加载init进程 | c.依序执行/sbin/init /etc/init /bin/init /bin/sh | | | | | | | +------------------------+-----------------------------------------------------------------------------------------------------------------------------+ kernel_init_freeable流程分析 ---------------------------- :: static noinline void __init kernel_init_freeable(void) { /* * Wait until kthreadd is all set-up. */ wait_for_completion(&kthreadd_done); //等待kernel thread kthreadd(pid=2)创建完毕 /* Now the scheduler is fully set up and can do blocking allocations */ gfp_allowed_mask = __GFP_BITS_MASK; //设置bitmask,使得init进程可以使用PM并且运行I/O阻塞操作 /* * init can allocate pages on any node */ set_mems_allowed(node_states[N_MEMORY]); //分配物理页面 cad_pid = task_pid(current); //设置目前运行进程init的pid号到cad_pid(cad_pid用来接收ctrl-alt-del reboot signal的进程，如果设置cad=1表示可以处理来自ctl-alt-del的动作)， //最后会调用ctrl_alt_del(void)函数并确认cad是否为1确定后将执行cad_work=deferred_cad,执行kernel_restart smp_prepare_cpus(setup_max_cpus); //体系结构相关的函数,实例在arch/arm64/kernel/smp.c中,调用smp_prepare_cpus时会以全局的setup_max_cpus为参数表示在编译核心时设定的CPU最大数量 workqueue_init(); //工作者队列初始化 init_mm_internals(); do_pre_smp_initcalls(); //实例在init/main.c中,会透过函数do_one_initcall执行symbol中__initcall_start与__initcall0_start之间的函数 lockup_detector_init(); smp_init(); //实例在kernel/smp.c中,函数主要是bootstrap处理器,运行active多核心架构下的其他处理器 sched_init_smp(); page_alloc_init_late(); /* Initialize page ext after all struct pages are initialized. */ page_ext_init(); do_basic_setup(); //实例在init/main.c中 /* Open the /dev/console on the rootfs, this should never fail */ if (ksys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0) pr_err("Warning: unable to open an initial console.\n"); (void) ksys_dup(0); (void) ksys_dup(0); /* * check if there is an early userspace init. If yes, let it do all * the work */ if (!ramdisk_execute_command) ramdisk_execute_command = "/init"; if (ksys_access((const char __user *) ramdisk_execute_command, 0) != 0) { ramdisk_execute_command = NULL; prepare_namespace(); } /* * Ok, we have completed the initial bootup, and * we're essentially up and running. Get rid of the * initmem segments and start the user-mode stuff.. * * rootfs is available now, try loading the public keys * and default modules */ integrity_load_keys(); } :: /* * Ok, the machine is now initialized. None of the devices * have been touched yet, but the CPU subsystem is up and * running, and memory and process management works. * * Now we can finally start doing some real work.. */ static void __init do_basic_setup(void) { cpuset_init_smp(); driver_init(); //函数实现位于drivers/base/init.c中,初始化linux driver system model init_irq_proc(); //初始化/proc/irq与其下的file node do_ctors(); // init/main.c中实现,执行位于__ctors_start和__ctors_end中得代码段 usermodehelper_enable(); //kernel/kmod.c中实现,产生khelper workqueue do_initcalls(); } :: static void __init do_initcalls(void) { int level; for (level = 0; level < ARRAY_SIZE(initcall_levels) - 1; level++) do_initcall_level(level); } //initcall函数调用,编译到内核中驱动在此函数中加载