linux系统（二）：内核及系统启动流程

“内核版本：linux-2.6”

linux系统基本启动流程如下：

开机->BOOT引导->grub引导->加载内核->启动系统

本文重点分析加载内核过程及系统启动流程。

（1）内核入口

系统进入内核的入口是/init/main.c的start_kernel()函数，这个相当于系统执行的第一个进程:

/*
* Activate the first processor. 启动第一个进程。
*/
asmlinkage void __init start_kernel(void)
{
char * command_line;
extern char saved_command_line[];
extern struct kernel_param __start___param[], __stop___param[];
/*
* Interrupts are still disabled. Do necessary setups, then
* enable them
*/
lock_kernel();
printk(linux_banner);
setup_arch(&command_line);
setup_per_zone_pages_min();
setup_per_cpu_areas();
/*
* Mark the boot cpu "online" so that it can call console drivers in
* printk() and can access its per-cpu storage.
*/
smp_prepare_boot_cpu();

build_all_zonelists();

page_alloc_init();

/* linux内存管理初始化，建立初始化节点和内存域的数据结构，建立内核的内存分配器，见下文1介绍 */

printk("Kernel command line: %s\n", saved_command_line);
parse_args("Booting kernel", command_line, __start___param,
__stop___param - __start___param,
&unknown_bootoption);
trap_init();

rcu_init();

/* 初始化 RCU同步机制 */

init_IRQ();

pidhash_init();

/* PID hash链表初始化，见下文2 */

sched_init();

/* 进程调度相关初始化 */

softirq_init();
time_init();

/*
* 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();
profile_init();
local_irq_enable();
#ifdef CONFIG_BLK_DEV_INITRD
if (initrd_start && !initrd_below_start_ok &&
initrd_start < min_low_pfn << PAGE_SHIFT) {
printk(KERN_CRIT "initrd overwritten (0x%08lx < 0x%08lx) - "
"disabling it.\n",initrd_start,min_low_pfn << PAGE_SHIFT);
initrd_start = 0;
}
#endif
page_address_init();
mem_init();
kmem_cache_init();
if (late_time_init)
late_time_init();
calibrate_delay();
pidmap_init();
pgtable_cache_init();
pte_chain_init();
fork_init(num_physpages);
proc_caches_init();
buffer_init();
security_scaffolding_startup();
vfs_caches_init(num_physpages);

radix_tree_init();

/* 基数树初始化，与文件系统内存管理相关 */

signals_init();
/* rootfs populating might need page-writeback */
page_writeback_init();
populate_rootfs();
#ifdef CONFIG_PROC_FS
proc_root_init();
#endif
check_bugs();
printk("POSIX conformance testing by UNIFIX\n");

/*
* We count on the initial thread going ok
* Like idlers init is an unlocked kernel thread, which will
* make syscalls (and thus be locked).
*/
init_idle(current, smp_processor_id());
/* 初始化 idle进程 */
/* Do the rest non-__init'ed, we're now alive */

rest_init();

/* 初始化 init进程并启动 */

}

（2）init进程