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5. 系统初始化
5.1. 系统初始化的主干线
Start_kernel() èsetup_arch() èreset_init() è kernel_thread(init …) è init() è do_basic_setup() èdriver_init() è do_initcall()
Start_kernel()函数负责初始化内核各个子系统，最后调用reset_init()，启动一个叫做init的内核线程，继续初始化。Start_kernel()函数在init/main.c中实现。
asmlinkage void __init start_kernel(void)
{
char * command_line;
extern struct kernel_param __start___param[], __stop___param[];
smp_setup_processor_id();
/*
* Need to run as early as possible, to initialize the
* lockdep hash:
*/
lockdep_init();
local_irq_disable();
early_boot_irqs_off();
early_init_irq_lock_class();
/*
* Interrupts are still disabled. Do necessary setups, then
* enable them
*/
lock_kernel();
boot_cpu_init();
page_address_init();
printk(KERN_NOTICE);
printk(linux_banner);
setup_arch(&command_line);
//setup processor and machine and destinate some pointers for do_initcalls() functions
// for example init_machine pointer is initialized with smdk_machine_init() function , and //init_machine() function is called by customize_machine(), and the function is processed by //arch_initcall(fn). Therefore smdk_machine_init() is issured. by edwin
setup_per_cpu_areas();
smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
/*
* 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();
/*
* Disable preemption - early bootup scheduling is extremely
* fragile until we cpu_idle() for the first time.
*/
preempt_disable();
build_all_zonelists();
page_alloc_init();
printk(KERN_NOTICE "Kernel command line: %s\n", saved_command_line);
parse_early_param();
parse_args("Booting kernel", command_line, __start___param,
__stop___param - __start___param,
&unknown_bootoption);
sort_main_extable();
unwind_init();
trap_init();
rcu_init();
init_IRQ();
pidhash_init();
init_timers();
hrtimers_init();
softirq_init();
timekeeping_init();
time_init();
profile_init();
if (!irqs_disabled())
printk("start_kernel(): bug: interrupts were enabled early\n" ;
early_boot_irqs_on();
local_irq_enable();
/*
* 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();
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();
#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
vfs_caches_init_early();
cpuset_init_early();
mem_init();
kmem_cache_init();
setup_per_cpu_pageset();
numa_policy_init();
if (late_time_init)
late_time_init();
calibrate_delay();
pidmap_init();
pgtable_cache_init();
prio_tree_init();
anon_vma_init();
#ifdef CONFIG_X86
if (efi_enabled)
efi_enter_virtual_mode();
#endif
fork_init(num_physpages);
proc_caches_init();
buffer_init();
unnamed_dev_init();
key_init();
security_init();
vfs_caches_init(num_physpages);
radix_tree_init();
signals_init();
/* rootfs populating might need page-writeback */
page_writeback_init();
#ifdef CONFIG_PROC_FS
proc_root_init();
#endif
cpuset_init();
taskstats_init_early();
delayacct_init();
check_bugs();
acpi_early_init(); /* before LAPIC and SMP init */
/* Do the rest non-__init'ed, we're now alive */
rest_init();
}
分析start_kernel()源码， 其中setup_arch() 和 reset_init()是两个比较关键的函数。下面将具体分析这两个函数。
5.2. setup_arch()函数分析
首先我们来分析下setup_arch()函数。
Setup_arch()函数主要工作是安装cpu和machine，并为start_kernel()后面的初始化函数指针指定值。
其中setup_processor()函数调用linux/arch/arm/kernel/head_common.S 中的lookup_processor_type函数查询处理器的型号并安装。
Setup_machine()函数调用inux/arch/arm/kernel/head_common.S 中的lookup_machine_type(__machine_arch_type)函数根据体系结构号__machine_arch_type，在__arch_info_begin和__arch_info_end段空间查询体系结构。问题是__machine_arch_type是在什么时候赋的初值？__arch_info_begin和__arch_info_end段空间到底放的是什么内容？
__machine_arch_type是一个全局变量，在linux/boot/decompress/misc.c的解压缩函数中得以赋值。
decompress_kernel(ulg output_start, ulg free_mem_ptr_p, ulg free_mem_ptr_end_p, int arch_id)
{
__machine_arch_type = arch_id;
}
__arch_info_begin和__arch_info_end段空间到底放的内容由链接器决定，存放是.arch.info.init段的内容。这个段是通过段属性__attribute__指定的。Grep一下.arch.info.init 得到./include/asm/mach/arch.h:53: __attribute__((__section__(".arch.info.init")) = { \ 在linux/include/asm-arm/mach/arch.h 中发现MACHINE_START宏定义。
#define MACHINE_START(_type,_name) \
static const struct machine_desc __mach_desc_##_type \
__attribute_used__ \
__attribute__((__section__(".arch.info.init")) = { \
.nr = MACH_TYPE_##_type, \
.name = _name,
#define MACHINE_END \
};
inux/arch/arm/mach-s3c2410/mach-smdk2410.c中对.arch.info.init段的初始化如下。
MACHINE_START(SMDK2410, "SMDK2410" /* @TODO: request a new identifier and switch
* to SMDK2410 */
/* Maintainer: Jonas Dietsche */
.phys_io = S3C2410_PA_UART,
.io_pg_offst = (((u32)S3C24XX_VA_UART) >> 1 & 0xfffc,
.boot_params = S3C2410_SDRAM_PA + 0x100,
.map_io = smdk2410_map_io,
.init_irq = s3c24xx_init_irq,
.init_machine = smdk_machine_init,
.timer = &s3c24xx_timer,
MACHINE_END
由此可见在.arch.info.init段内存放了__desc_mach_desc_SMDK2410结构体。初始化了相应的初始化函数指针。问题又来了， 这些初始化指针函数是什么时候被调用的呢？
分析发现，不一而同。
如s3c24xx_init_irq()函数是通过start_kernel()里的init_IRQ()函数调用init_arch_irq()实现的。因为在MACHINE_START结构体中 .init_irq = s3c24xx_init_irq，而在setup_arch()函数中init_arch_irq = mdesc->init_irq， 所以调用init_arch_irq()就相当于调用了s3c24xx_init_irq()。
又如smdk_machine_init()函数的初始化。在MACHINE_START结构体中，函数指针赋值，.init_machine = smdk_machine_init。而init_machine()函数被linux/arch/arm/kernel/setup.c文件中的customize_machine()函数调用并被arch_initcall(Fn)宏处理，arch_initcall(customize_machine)。 被arch_initcall(Fn)宏处理过函数将linux/init/main.c
do_initcalls()函数调用。 具体参看下边的部分。
void __init setup_arch(char **cmdline_p)
{
struct tag *tags = (struct tag *)&init_tags;
struct machine_desc *mdesc;
char *from = default_command_line;
setup_processor();
mdesc = setup_machine(machine_arch_type);//machine_arch_type =SMDK2410 by edwin
machine_name = mdesc->name;
if (mdesc->soft_reboot)
reboot_setup("s";
if (mdesc->boot_params)
tags = phys_to_virt(mdesc->boot_params);
/*
* If we have the old style parameters, convert them to
* a tag list.
*/
if (tags->hdr.tag != ATAG_CORE)
convert_to_tag_list(tags);
if (tags->hdr.tag != ATAG_CORE)
tags = (struct tag *)&init_tags;
if (mdesc->fixup)
mdesc->fixup(mdesc, tags, &from, &meminfo);
if (tags->hdr.tag == ATAG_CORE) {
if (meminfo.nr_banks != 0)
squash_mem_tags(tags);
parse_tags(tags);
}
init_mm.start_code = (unsigned long) &_text;
init_mm.end_code = (unsigned long) &_etext;
init_mm.end_data = (unsigned long) &_edata;
init_mm.brk = (unsigned long) &_end;
memcpy(saved_command_line, from, COMMAND_LINE_SIZE);
saved_command_line[COMMAND_LINE_SIZE-1] = '\0';
parse_cmdline(cmdline_p, from);
paging_init(&meminfo, mdesc);
request_standard_resources(&meminfo, mdesc);
#ifdef CONFIG_SMP
smp_init_cpus();
#endif
cpu_init();
/*
* Set up various architecture-specific pointers
*/
init_arch_irq = mdesc->init_irq;
system_timer = mdesc->timer;
init_machine = mdesc->init_machine;
#ifdef CONFIG_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 we're going to be the grim
* reaper of innocent orphaned children.
*
* We don't 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
* we're 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 isn't (%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
}
5.3.2. 初始化设备5.3.3. 驱动程序
linux/init/main.c
static void __init do_basic_setup(void)
{
/* drivers will send hotplug events */
init_workqueues();
usermodehelper_init();
driver_init(); /* 初始化驱动程序模型。调用驱动初始化函数初始化子系统。 */
#ifdef CONFIG_SYSCTL
sysctl_init();
#endif
do_initcalls();
}
linux/init/main.c
extern initcall_t __initcall_start[], __initcall_end[];
static void __init do_initcalls(void)
{
initcall_t *call;
int count = preempt_count();
for (call = __initcall_start; call < __initcall_end; call++) {
char *msg = NULL;
char msgbuf[40];
int result;
if (initcall_debug) {
printk("Calling initcall 0x%p", *call);
print_fn_descriptor_symbol(": %s()",
(unsigned long) *call);
printk("\n");
}
result = (*call)();
……
……
……
}
/* Make sure there is no pending stuff from the initcall sequence */
flush_scheduled_work();
}
分析上面一段代码可以看出，设备的初始化是通过do_basic_setup()函数调用do_initcalls()函数，实现__initcall_start, __initcall_end段之间的指针函数执行的。而到底是那些驱动函数怎么会被集中到这个段内的呢？我们知道系统内存空间的分配是由链接器ld读取链接脚本文件决定。链接器将同样属性的文件组织到相同的段里面去，如所有的.text段都被放在一起。在链接脚本里面可以获得某块内存空间的具体地址。我们来看下linux-2.6.18.8\arch\arm\kernel\vmlinux.lds.S文件。由于文件过长，只贴出和__initcall_start, __initcall_end相关的部分。
__initcall_start = .;
*(.initcall1.init)
*(.initcall2.init)
*(.initcall3.init)
*(.initcall4.init)
*(.initcall5.init)
*(.initcall6.init)
*(.initcall7.init)
__initcall_end = .;
从脚本文件中我们可以看出， 在__initcall_start, __initcall_end之间放置的是属行为(.initcall*.init)的函数数据 。在linux/include/linux/init.h文件中可以知道，(.initcall*.init)属性是由__define_initcall(level, fn)宏设定的。
#define __define_initcall(level,fn) \
static initcall_t __initcall_##fn __attribute_used__ \
__attribute__((__section__(".initcall" level ".init"))) = fn
#define core_initcall(fn) __define_initcall("1",fn)
#define postcore_initcall(fn) __define_initcall("2",fn)
#define arch_initcall(fn) __define_initcall("3",fn)
#define subsys_initcall(fn) __define_initcall("4",fn)
#define fs_initcall(fn) __define_initcall("5",fn)
#define device_initcall(fn) __define_initcall("6",fn)
#define late_initcall(fn) __define_initcall("7",fn)
#define __initcall(fn) device_initcall(fn)
由此可以判断，所有的设备驱动函数都必然通过*_initcall(fn)宏的处理。以此为入口，可以查询所有的设备驱动。
core_initcall(fn)
static int __init consistent_init(void) linux/arch/arm/mm/consistent.c
static int __init v6_userpage_init(void) linux/arch/arm/mm/copypage-v6.c
static int __init init_dma(void) linux/arch/arm/kernel/dma.c
static int __init s3c2410_core_init(void) linux/arch/arm/mach-s3c2410/s3c2410.c
postcore_initcall(fn)
static int ecard_bus_init(void) linux/arch/arm/kernel/ecard.c
arch_initcall(fn)
static __init int bast_irq_init(void) linux/arch/arm/mach-s3c2410/bast-irq.c
static int __init s3c_arch_init(void) linux/arch/arm/mach-s3c2410/cpu.c
static __init int pm_simtec_init(void) linux/arch/arm/mach-s3c2410/pm-simtec.c
static int __init customize_machine(void) linux/arch/arm/kernel/setup.c
subsys_initcall(fn)
static int __init ecard_init(void) linux/arch/arm/kernel/ecard.c
int __init scoop_init(void) linux/arch/arm/common/scoop.c
static int __init topology_init(void) linux/arch/arm/kernel/setup.c
fs_initcall(fn)
static int __init alignment_init(void) linux/arch/arm/mm/alignment.c
device_initcall(fn)
static int __init leds_init(void) linux/arch/arm/kernel/time.c
static int __init timer_init_sysfs(void) linux/arch/arm/kernel/time.c
late_initcall(fn)
static int __init crunch_init(void) arch/arm/kernel/crunch.c
static int __init arm_mrc_hook_init(void) linux/arch/arm/kernel/traps.c
5.3.4. 启动用户空间的程序
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发表于 2009-01-06 00:25
发表于 2009-01-06 08:54