Start_Kernel之一 ------勇敢的猜想和胡言乱语

进入start_kernel就是进入了kernel启动的主线。其定义在init/main.c里面。start_kernel里面包含了一长串的init代码。看实际代码之前，我来猜一下有哪些需要初始化的：

1. CPU和SMP的初始化的初始化

2. 内存管理的初始化

3. 互斥和同步

4. 进程管理

5. 文件系统

6. 各类总线的初始化

7. 初始化硬件设备

好了，回头看看代码里面到底做了哪些初始化（以下的注解都是望文生义，我会随着以后对于每个模块的源码解读进行更新）：

asmlinkage void __init start_kernel(void)
{
    char * command_line;
    extern const struct kernel_param __start___param[], __stop___param[];

    smp_setup_processor_id(); //确定SMP系统中每个CPU的id

    /*
     * Need to run as early as possible, to initialize the
     * lockdep hash:
     */
    lockdep_init(); //初始化互斥锁的dependency。
    debug_objects_early_init(); //初始化debug kernel相关

    /*
     * Set up the the initial canary ASAP:
     */
    boot_init_stack_canary(); //stack_canary的是带防止栈溢出攻击保护的堆栈。

    cgroup_init_early(); //cgroup是什么？？有待查找

    local_irq_disable(); //这个太直白了。
    early_boot_irqs_off(); //这个也很直白。

/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 */
    tick_init(); //初始化time ticket，时钟
    boot_cpu_init(); //用以启动的CPU进行初始化。也就是初始化CPU0
    page_address_init();//初始化页面
    printk(KERN_NOTICE "%s", linux_banner);
    setup_arch(&command_line); //CPU架构相关的初始化
    mm_init_owner(&init_mm, &init_task); //初始化内存管理
    setup_command_line(command_line); //处理启动命令行
    setup_nr_cpu_ids(); //nr_cpu_id是什么？
    setup_per_cpu_areas(); //为每个CPU开辟一块区域？
    smp_prepare_boot_cpu();//准备boot_cpu.   /* arch-specific boot-cpu hooks */

    build_all_zonelists(NULL); //建立什么样的zone??
    page_alloc_init(); //初始化page allocation相关结构

    printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line);
    parse_early_param();
    parse_args("Booting kernel", static_command_line, __start___param,
           __stop___param - __start___param,
           &unknown_bootoption);//解析启动参数
    /*
     * These use large bootmem allocations and must precede
     * kmem_cache_init()
     */
    pidhash_init();//初始化process ID hash表
    vfs_caches_init_early(); //文件系统caches预初始化
    sort_main_extable(); //初始化exception table
    trap_init(); //初始化trap，用以处理错误执行代码
    mm_init(); //初始化内存管理
    /*
     * Set up the scheduler prior starting any interrupts (such as the
     * timer interrupt). Full topology setup happens at smp_init()
     * time - but meanwhile we still have a functioning scheduler.
     */
    sched_init(); //进程调度初始化
    /*
     * Disable preemption - early bootup scheduling is extremely
     * fragile until we cpu_idle() for the first time.
     */
    preempt_disable(); //这个是什么东东？
    if (!irqs_disabled()) {
        printk(KERN_WARNING "start_kernel(): bug: interrupts were "
                "enabled *very* early, fixing it\n");
        local_irq_disable();
    }
    rcu_init(); //Read_Copy_Update机制初始
    radix_tree_init(); //什么是radlx_tree
    /* init some links before init_ISA_irqs() */
    early_irq_init();
    init_IRQ(); //初始化中断
    prio_tree_init(); //这是啥？以后要弄懂
    init_timers(); //初始化时钟
    hrtimers_init();//初始化高精时钟
    softirq_init();//初始化软中断
    timekeeping_init();//初始化时钟源
    time_init();//初始化时间例程
    profile_init(); //Profile?这是什么profile?
    if (!irqs_disabled())
        printk(KERN_CRIT "start_kernel(): bug: interrupts were "
                 "enabled early\n");
    early_boot_irqs_on();
    local_irq_enable();

    /* Interrupts are enabled now so all GFP allocations are safe. */
    gfp_allowed_mask = __GFP_BITS_MASK;

    kmem_cache_init_late();//初始化CPU Cache

    /*
     * HACK ALERT! This is early. We're enabling the console before
     * we've done PCI setups etc, and console_init() must be aware of
     * this. But we do want output early, in case something goes wrong.
     */
    console_init(); //初始化console
    if (panic_later)
        panic(panic_later, panic_param);

    lockdep_info();

    /*
     * Need to run this when irqs are enabled, because it wants
     * to self-test [hard/soft]-irqs on/off lock inversion bugs
     * too:
     */
    locking_selftest(); //自测试锁

#ifdef CONFIG_BLK_DEV_INITRD
    if (initrd_start && !initrd_below_start_ok &&
        page_to_pfn(virt_to_page((void *)initrd_start)) < min_low_pfn) {
        printk(KERN_CRIT "initrd overwritten (0x%08lx < 0x%08lx) - "
            "disabling it.\n",
            page_to_pfn(virt_to_page((void *)initrd_start)),
            min_low_pfn);
        initrd_start = 0;
    }
#endif
    page_cgroup_init(); //页面初始
    enable_debug_pagealloc(); //页面分配debug启用
    kmemleak_init(); //memory leak 侦测初始化
    debug_objects_mem_init(); //debug object是什么？
    idr_init_cache(); //idr是什么？
    setup_per_cpu_pageset(); //设置每个CPU的页面集合
    numa_policy_init();// NUMA (Non Uniform Memory Access) policy
    if (late_time_init)
        late_time_init();
    sched_clock_init();//初始化调度时钟
    calibrate_delay(); //协同不同CPU的时钟
    pidmap_init();//pid是process id还是processor id?
    anon_vma_init();//anonymous page?什么意思？
#ifdef CONFIG_X86
    if (efi_enabled)
        efi_enter_virtual_mode();
#endif
    thread_info_cache_init(); //初始化thread info
    cred_init(); //credential
    fork_init(totalram_pages); //初始化fork
    proc_caches_init(); //初始化/proc的cache?
    buffer_init(); // buffer
    key_init(); //key
    security_init();//security
    dbg_late_init();//debug
    vfs_caches_init(totalram_pages);//文件系统cache初始化
    signals_init();//signal
    /* rootfs populating might need page-writeback */
    page_writeback_init();page_writeback
#ifdef CONFIG_PROC_FS
    proc_root_init();
#endif
    cgroup_init(); //cgroup?
    cpuset_init(); //cpuset
    taskstats_init_early(); //task
    delayacct_init();

    check_bugs(); //检查什么bug?

    acpi_early_init();//acpi /* before LAPIC and SMP init */
    sfi_init_late(); //simple firmware interface

    ftrace_init();

    /* Do the rest non-__init'ed, we're now alive */
    rest_init();
}

将这些函数归归类，以后就按照类型来读：

CPU初始化

smp_setup_processor_id()

boot_cpu_init()

setup_arch(&command_line);

setup_nr_cpu_ids()

setup_per_cpu_areas()

smp_prepare_boot_cpu()

setup_per_cpu_pageset(); 

calibrate_delay();

cpuset_init();

内存管理初始化

boot_init_stack_canary()

page_address_init();

mm_init_owner();

page_alloc_init(); 

mm_init();

rcu_init();

kmem_cache_init_late();

page_cgroup_init(); 

kmemleak_init(); 

numa_policy_init();

anon_vma_init();

page_writeback_init();

进程管理

pidhash_init();

sched_init(); 

sched_clock_init()

pidmap_init();

fork_init(totalram_pages); 

taskstats_init_early();

文件系统

vfs_caches_init_early(); 

thread_info_cache_init();

vfs_caches_init(totalram_pages);

中断

early_irq_init();

init_IRQ(); 

softirq_init();

同步互斥

lockdep_init();

lockdep_info();

locking_selftest(); 

时钟

tick_init(); 

init_timers(); 

hrtimers_init();

timekeeping_init();

time_init();

调试

debug_objects_early_init();

console_init();

enable_debug_pagealloc(); 

debug_objects_mem_init();

dbg_late_init();

其他

sort_main_extable();

trap_init(); 

efi_enter_virtual_mode();

cred_init(); 

proc_caches_init(); 

buffer_init();

key_init(); 

security_init();

signals_init();

proc_root_init();

delayacct_init();

check_bugs();

acpi_early_init();

sfi_init_late(); 

未知

cgroup_init_early();

build_all_zonelists(NULL); 

preempt_disable();

radix_tree_init();

prio_tree_init(); 

profile_init();

idr_init_cache(); 

cgroup_init();

ftrace_init();