Arm linux 内核移植及系统初始化过程分析

FIG_VT
#if defined(CONFIG_VGA_CONSOLE)
conswitchp = &vga_con;
#elif defined(CONFIG_DUMMY_CONSOLE)
conswitchp = &dummy_con;
#endif
#endif
}
5.3. rest_init()函数分析
下面我们来分析下rest_init()函数。
Start_kernel()函数负责初始化内核各子系统，最后调用reset_init()，启动一个叫做init的内核线程，继续初始化。在init内核线程中，将执行下列init()函数的程序。Init()函数负责完成根文件系统的挂接、初始化设备驱动程序和启动用户空间的init进程等重要工作。

static void noinline rest_init(void)
__releases(kernel_lock)
{
kernel_thread(init, NULL, CLONE_FS | CLONE_SIGHAND);
numa_default_policy();
unlock_kernel();

/*
* The boot idle thread must execute schedule()
* at least one to get things moving:
*/
preempt_enable_no_resched();
schedule();
preempt_disable();

/* Call into cpu_idle with preempt disabled */
cpu_idle();
}

static int init(void * unused)
{
lock_kernel();
/*
* init can run on any cpu.
*/
set_cpus_allowed(current, CPU_MASK_ALL);
/*
* Tell the world that were going to be the grim
* reaper of innocent orphaned children.
*
* We dont want people to have to make incorrect
* assumptions about where in the task array this
* can be found.
*/
child_reaper = current;

smp_prepare_cpus(max_cpus);

do_pre_smp_initcalls();

smp_init();
sched_init_smp();

cpuset_init_smp();

/*
* Do this before initcalls, because some drivers want to access
* firmware files.
*/
populate_rootfs(); //挂接根文件系统

do_basic_setup(); //初始化设备驱动程序

/*
* check if there is an early userspace init. If yes, let it do all
* the work //启动用户空间的init进程
*/

if (!ramdisk_execute_command)
ramdisk_execute_command = "/init";

if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
ramdisk_execute_command = NULL;
prepare_namespace();
}

/*
* Ok, we have completed the initial bootup, and
* were essentially up and running. Get rid of the
* initmem segments and start the user-mode stuff..
*/
free_initmem();
unlock_kernel();
mark_rodata_ro();
system_state = SYSTEM_RUNNING;
numa_default_policy();

if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
printk(KERN_WARNING "Warning: unable to open an initial console./n");

(void) sys_dup(0);
(void) sys_dup(0);

if (ramdisk_execute_command) {
run_init_process(ramdisk_execute_command);
printk(KERN_WARNING "Failed to execute %s/n",
ramdisk_execute_command);
}

/*
* 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) {
run_init_process(execute_command);
printk(KERN_WARNING "Failed to execute %s. Attempting "
"defaults.../n", execute_command);
}
run_init_process("/sbin/init");
run_init_process("/etc/init");
run_init_process("/bin/init");
run_init_process("/bin/sh");

panic("No init found. Try passing init= option to kernel.");
}

5.3.1. 挂接根文件系统
Linux/init/ramfs.c
void __init populate_rootfs(void)
{
char *err = unpack_to_rootfs(__initramfs_start,
__initramfs_end - __initramfs_start, 0);
if (err)
panic(err);
#ifdef CONFIG_BLK_DEV_INITRD
if (initrd_start) {
#ifdef CONFIG_BLK_DEV_RAM
int fd;
printk(KERN_INFO "checking if image is initramfs...");
err = unpack_to_rootfs((char *)initrd_start,
initrd_end - initrd_start, 1);
if (!err) {
printk(" it is/n");
unpack_to_rootfs((char *)initrd_start,
initrd_end - initrd_start, 0);
free_initrd();
return;
}
printk("it isnt (%s); looks like an initrd/n", err);
fd = sys_open("/initrd.image", O_WRONLY|O_CREAT, 0700);
if (fd >= 0) {
sys_write(fd, (char *)initrd_start,
initrd_end - initrd_start);
sys_close(fd);
free_initrd();
}
#else
printk(KERN_INFO "Unpacking initramfs...");
err = unpack_to_rootfs((char *)initrd_start,
initrd_end - initrd_start, 0);
if (err)
panic(err);
printk(" done/n");
free_initrd();
#endif
}
#endif
}