本篇內(nèi)容主要講解“l(fā)inux內(nèi)核是否有main函數(shù)”,感興趣的朋友不妨來看看。本文介紹的方法操作簡(jiǎn)單快捷,實(shí)用性強(qiáng)。下面就讓小編來帶大家學(xué)習(xí)“l(fā)inux內(nèi)核是否有main函數(shù)”吧!
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linux內(nèi)核有main函數(shù);main函數(shù)是程序的入口,main是應(yīng)用程序和操作系統(tǒng)之間約定好的一個(gè)接口名,所以linux中每個(gè)應(yīng)用程序的第一個(gè)函數(shù)必須是main。
linux內(nèi)核源碼之main函數(shù)解析
這幾天一直在糾結(jié):
main函數(shù)是程序的入口,一個(gè)程序啟動(dòng)后,經(jīng)過bootloader的初始化就該經(jīng)main函數(shù)進(jìn)入C語言的世界,但是linux中每個(gè)應(yīng)用程序的開始都是從main函數(shù)開始的。linux下有多個(gè)應(yīng)用程序,豈不是有很多個(gè)main。那bootloader會(huì)知道跳到哪個(gè)main?多個(gè)main編譯怎么不沖突?
在網(wǎng)上搜索了很久,漸漸的有些明白了:
1、main函數(shù)是C語言的入口,這句話沒錯(cuò);但是這句話僅僅是一個(gè)約定,而非一個(gè)亙古不變的鐵律!從程序的更為本質(zhì)的匯編代碼來看,只是大家約定匯編初始化完了后,跳到一個(gè)名字叫"main"的標(biāo)號(hào)處;言外之意就是這個(gè)標(biāo)號(hào)也是可以改名的,比如linux的C語言入口就是start_kernel();從這個(gè)標(biāo)號(hào)地址后就是C語言的天下了。用main這個(gè)名字僅僅是因?yàn)榇蠹业募s定而已,不遵守約定能玩的轉(zhuǎn)也行啊,就像蘋果充電線啥的都和別人不一樣。
2、在編譯時(shí)是不存多個(gè)main函數(shù)的!每個(gè)應(yīng)用程序雖說都有一個(gè)main函數(shù)(從應(yīng)用程序來看應(yīng)用程序的入口是main函數(shù)哦);但是應(yīng)用程序都是獨(dú)立編譯的,不會(huì)一起編譯,操作系統(tǒng)內(nèi)核就更不可能和應(yīng)用程序一起編譯了!所以根本不存在多個(gè)main沖突的??!可能是統(tǒng)一操作系統(tǒng)與應(yīng)用程序之間的接口,亦或是側(cè)面影響下main是程序入口的說法,main是應(yīng)用程序和操作系統(tǒng)之間約定好的一個(gè)接口名!所以linux中每個(gè)應(yīng)用程序的第一個(gè)函數(shù)必須是main。除非你改掉了內(nèi)核調(diào)度的接口地方。
3、linux的應(yīng)用程序的安裝啟動(dòng)也可以類比下我們每天都在用的Windows。Windows應(yīng)用程序的安裝其實(shí)也是把一些執(zhí)行文件拷貝到指定的文件夾里(從綠色軟件看),點(diǎn)擊就可以運(yùn)行。linux下也是這樣。編譯好的bin文件放到指定的文件夾目錄下,然后用命令啟動(dòng)執(zhí)行。
/*
* linux/init/main.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*
* GK 2/5/95 - Changed to support mounting root fs via NFS
* Added initrd & change_root: Werner Almesberger & Hans Lermen, Feb '96
* Moan early if gcc is old, avoiding bogus kernels - Paul Gortmaker, May '96
* Simplified starting of init: Michael A. Griffith <grif@acm.org>
* start_kernel->rest_init->kernel_init創(chuàng)建用戶init pid=1
->kthreadd管理內(nèi)核線程 pid=x
->pid=0,是idle線程
在rest_init中,會(huì)創(chuàng)建kernel_init線程,它負(fù)責(zé)創(chuàng)建用戶init進(jìn)程,完成工作后,自己
化身為idle線程
*/
#include <linux/types.h>
#include <linux/module.h>
#include <linux/proc_fs.h>
#include <linux/kernel.h>
#include <linux/syscalls.h>
#include <linux/stackprotector.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <linux/delay.h>
#include <linux/ioport.h>
#include <linux/init.h>
#include <linux/initrd.h>
#include <linux/bootmem.h>
#include <linux/acpi.h>
#include <linux/tty.h>
#include <linux/percpu.h>
#include <linux/kmod.h>
#include <linux/vmalloc.h>
#include <linux/kernel_stat.h>
#include <linux/start_kernel.h>
#include <linux/security.h>
#include <linux/smp.h>
#include <linux/profile.h>
#include <linux/rcupdate.h>
#include <linux/moduleparam.h>
#include <linux/kallsyms.h>
#include <linux/writeback.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/cgroup.h>
#include <linux/efi.h>
#include <linux/tick.h>
#include <linux/interrupt.h>
#include <linux/taskstats_kern.h>
#include <linux/delayacct.h>
#include <linux/unistd.h>
#include <linux/rmap.h>
#include <linux/mempolicy.h>
#include <linux/key.h>
#include <linux/buffer_head.h>
#include <linux/page_cgroup.h>
#include <linux/debug_locks.h>
#include <linux/debugobjects.h>
#include <linux/lockdep.h>
#include <linux/kmemleak.h>
#include <linux/pid_namespace.h>
#include <linux/device.h>
#include <linux/kthread.h>
#include <linux/sched.h>
#include <linux/signal.h>
#include <linux/idr.h>
#include <linux/kgdb.h>
#include <linux/ftrace.h>
#include <linux/async.h>
#include <linux/kmemcheck.h>
#include <linux/sfi.h>
#include <linux/shmem_fs.h>
#include <linux/slab.h>
#include <linux/perf_event.h>
#include <asm/io.h>
#include <asm/bugs.h>
#include <asm/setup.h>
#include <asm/sections.h>
#include <asm/cacheflush.h>
#ifdef CONFIG_X86_LOCAL_APIC
#include <asm/smp.h>
#endif
static int kernel_init(void *);
extern void init_IRQ(void);
extern void fork_init(unsigned long);
extern void mca_init(void);
extern void sbus_init(void);
extern void prio_tree_init(void);
extern void radix_tree_init(void);
#ifndef CONFIG_DEBUG_RODATA
static inline void mark_rodata_ro(void) { }
#endif
#ifdef CONFIG_TC
extern void tc_init(void);
#endif
/*
* Debug helper: via this flag we know that we are in 'early bootup code'
* where only the boot processor is running with IRQ disabled. This means
* two things - IRQ must not be enabled before the flag is cleared and some
* operations which are not allowed with IRQ disabled are allowed while the
* flag is set.
*/
bool early_boot_irqs_disabled __read_mostly;
enum system_states system_state __read_mostly;
EXPORT_SYMBOL(system_state);
/*
* Boot command-line arguments
*/
#define MAX_INIT_ARGS CONFIG_INIT_ENV_ARG_LIMIT
#define MAX_INIT_ENVS CONFIG_INIT_ENV_ARG_LIMIT
extern void time_init(void);
/* Default late time init is NULL. archs can override this later. */
void (*__initdata late_time_init)(void);
extern void softirq_init(void);
/* Untouched command line saved by arch-specific code. */
char __initdata boot_command_line[COMMAND_LINE_SIZE];
/* Untouched saved command line (eg. for /proc) */
char *saved_command_line;
/* Command line for parameter parsing */
static char *static_command_line;
static char *execute_command;
static char *ramdisk_execute_command;
/*
* If set, this is an indication to the drivers that reset the underlying
* device before going ahead with the initialization otherwise driver might
* rely on the BIOS and skip the reset operation.
*
* This is useful if kernel is booting in an unreliable environment.
* For ex. kdump situaiton where previous kernel has crashed, BIOS has been
* skipped and devices will be in unknown state.
*/
unsigned int reset_devices;
EXPORT_SYMBOL(reset_devices);
static int __init set_reset_devices(char *str)
{
reset_devices = 1;
return 1;
}
__setup("reset_devices", set_reset_devices);
static const char * argv_init[MAX_INIT_ARGS+2] = { "init", NULL, };
const char * envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
static const char *panic_later, *panic_param;
extern const struct obs_kernel_param __setup_start[], __setup_end[];
static int __init obsolete_checksetup(char *line)
{
const struct obs_kernel_param *p;
int had_early_param = 0;
p = __setup_start;
do {
int n = strlen(p->str);
if (parameqn(line, p->str, n)) {
if (p->early) {
/* Already done in parse_early_param?
* (Needs exact match on param part).
* Keep iterating, as we can have early
* params and __setups of same names 8( */
if (line[n] == '\0' || line[n] == '=')
had_early_param = 1;
} else if (!p->setup_func) {
printk(KERN_WARNING "Parameter %s is obsolete,"
" ignored\n", p->str);
return 1;
} else if (p->setup_func(line + n))
return 1;
}
p++;
} while (p < __setup_end);
return had_early_param;
}
/*
* This should be approx 2 Bo*oMips to start (note initial shift), and will
* still work even if initially too large, it will just take slightly longer
*/
unsigned long loops_per_jiffy = (1<<12);
EXPORT_SYMBOL(loops_per_jiffy);
static int __init debug_kernel(char *str)
{
console_loglevel = 10;
return 0;
}
static int __init quiet_kernel(char *str)
{
console_loglevel = 4;
return 0;
}
early_param("debug", debug_kernel);
early_param("quiet", quiet_kernel);
static int __init loglevel(char *str)
{
int newlevel;
/*
* Only update loglevel value when a correct setting was passed,
* to prevent blind crashes (when loglevel being set to 0) that
* are quite hard to debug
*/
if (get_option(&str, &newlevel)) {
console_loglevel = newlevel;
return 0;
}
return -EINVAL;
}
early_param("loglevel", loglevel);
/* Change NUL term back to "=", to make "param" the whole string. */
static int __init repair_env_string(char *param, char *val)
{
if (val) {
/* param=val or param="val"? */
if (val == param+strlen(param)+1)
val[-1] = '=';
else if (val == param+strlen(param)+2) {
val[-2] = '=';
memmove(val-1, val, strlen(val)+1);
val--;
} else
BUG();
}
return 0;
}
/*
* Unknown boot options get handed to init, unless they look like
* unused parameters (modprobe will find them in /proc/cmdline).
*/
static int __init unknown_bootoption(char *param, char *val)
{
repair_env_string(param, val);
/* Handle obsolete-style parameters */
if (obsolete_checksetup(param))
return 0;
/* Unused module parameter. */
if (strchr(param, '.') && (!val || strchr(param, '.') < val))
return 0;
if (panic_later)
return 0;
if (val) {
/* Environment option */
unsigned int i;
for (i = 0; envp_init[i]; i++) {
if (i == MAX_INIT_ENVS) {
panic_later = "Too many boot env vars at `%s'";
panic_param = param;
}
if (!strncmp(param, envp_init[i], val - param))
break;
}
envp_init[i] = param;
} else {
/* Command line option */
unsigned int i;
for (i = 0; argv_init[i]; i++) {
if (i == MAX_INIT_ARGS) {
panic_later = "Too many boot init vars at `%s'";
panic_param = param;
}
}
argv_init[i] = param;
}
return 0;
}
static int __init init_setup(char *str)
{
unsigned int i;
execute_command = str;
/*
* In case LILO is going to boot us with default command line,
* it prepends "auto" before the whole cmdline which makes
* the shell think it should execute a script with such name.
* So we ignore all arguments entered _before_ init=... [MJ]
*/
for (i = 1; i < MAX_INIT_ARGS; i++)
argv_init[i] = NULL;
return 1;
}
__setup("init=", init_setup);
static int __init rdinit_setup(char *str)
{
unsigned int i;
ramdisk_execute_command = str;
/* See "auto" comment in init_setup */
for (i = 1; i < MAX_INIT_ARGS; i++)
argv_init[i] = NULL;
return 1;
}
__setup("rdinit=", rdinit_setup);
#ifndef CONFIG_SMP
static const unsigned int setup_max_cpus = NR_CPUS;
#ifdef CONFIG_X86_LOCAL_APIC
static void __init smp_init(void)
{
APIC_init_uniprocessor();
}
#else
#define smp_init() do { } while (0)
#endif
static inline void setup_nr_cpu_ids(void) { }
static inline void smp_prepare_cpus(unsigned int maxcpus) { }
#endif
/*
* We need to store the untouched command line for future reference.
* We also need to store the touched command line since the parameter
* parsing is performed in place, and we should allow a component to
* store reference of name/value for future reference.
*/
static void __init setup_command_line(char *command_line)
{
saved_command_line = alloc_bootmem(strlen (boot_command_line)+1);
static_command_line = alloc_bootmem(strlen (command_line)+1);
strcpy (saved_command_line, boot_command_line);
strcpy (static_command_line, command_line);
}
/*
* We need to finalize in a non-__init function or else race conditions
* between the root thread and the init thread may cause start_kernel to
* be reaped by free_initmem before the root thread has proceeded to
* cpu_idle.
*
* gcc-3.4 accidentally inlines this function, so use noinline.
*/
static __initdata DECLARE_COMPLETION(kthreadd_done);
static noinline void __init_refok rest_init(void)
{
int pid;
rcu_scheduler_starting();//READ-COPY UPDATE啟動(dòng)
/*
* We need to spawn init first so that it obtains pid 1, however
* the init task will end up wanting to create kthreads, which, if
* we schedule it before we create kthreadd, will OOPS.
* 創(chuàng)建一個(gè)內(nèi)核線程,它的線程函數(shù)是kernel_init,pid=1,內(nèi)核進(jìn)程
*/
kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
//numa策略設(shè)置
numa_default_policy();
//全局鏈表kthread_create_list中的kthread內(nèi)核線程都被運(yùn)行
//kthreadd線程管理和調(diào)度其它內(nèi)核線程
pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
rcu_read_lock();
//通過pid,ini_pid_ns取得kthreadd地址
kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
rcu_read_unlock();
//通知在kthreadd_done條件的kernel_init線程
complete(&kthreadd_done);
/*
* The boot idle thread must execute schedule()
* at least once to get things moving:
* idle 線程初始化
*/
init_idle_bootup_task(current);
//搶占禁用
schedule_preempt_disabled();
/* Call into cpu_idle with preempt disabled */
cpu_idle();
}
/* Check for early params. */
static int __init do_early_param(char *param, char *val)
{
const struct obs_kernel_param *p;
for (p = __setup_start; p < __setup_end; p++) {
if ((p->early && parameq(param, p->str)) ||
(strcmp(param, "console") == 0 &&
strcmp(p->str, "earlycon") == 0)
) {
if (p->setup_func(val) != 0)
printk(KERN_WARNING
"Malformed early option '%s'\n", param);
}
}
/* We accept everything at this stage. */
return 0;
}
void __init parse_early_options(char *cmdline)
{
parse_args("early options", cmdline, NULL, 0, 0, 0, do_early_param);
}
/* Arch code calls this early on, or if not, just before other parsing. */
void __init parse_early_param(void)
{
static __initdata int done = 0;
static __initdata char tmp_cmdline[COMMAND_LINE_SIZE];
if (done)
return;
/* All fall through to do_early_param. */
strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
parse_early_options(tmp_cmdline);
done = 1;
}
/*
* Activate the first processor.
*/
static void __init boot_cpu_init(void)
{
int cpu = smp_processor_id();
/* Mark the boot cpu "present", "online" etc for SMP and UP case */
set_cpu_online(cpu, true);
set_cpu_active(cpu, true);
set_cpu_present(cpu, true);
set_cpu_possible(cpu, true);
}
void __init __weak smp_setup_processor_id(void)
{
}
void __init __weak thread_info_cache_init(void)
{
}
/*
* Set up kernel memory allocators
*/
static void __init mm_init(void)
{
/*
* page_cgroup requires contiguous pages,
* bigger than MAX_ORDER unless SPARSEMEM.
*/
page_cgroup_init_flatmem();
mem_init();
kmem_cache_init();
percpu_init_late();
pgtable_cache_init();
vmalloc_init();
}
asmlinkage void __init start_kernel(void)
{
char * command_line;
extern const struct kernel_param __start___param[], __stop___param[];
/*
* Need to run as early as possible, to initialize the
* lockdep hash:
*/
//初始化2個(gè)hash表-Lock Dependency Validator(內(nèi)核依賴的關(guān)系表)
lockdep_init();
smp_setup_processor_id(); //空函數(shù)
debug_objects_early_init();//初始化內(nèi)核調(diào)試相關(guān)
/*
* Set up the the initial canary ASAP:
*/
boot_init_stack_canary();//棧溢出保護(hù)初始化
//控制組初始化-cgroup-資源任務(wù)分組管理
cgroup_init_early();
local_irq_disable();//關(guān)中斷
early_boot_irqs_disabled = true;
/*
* Interrupts are still disabled. Do necessary setups, then
* enable them
*/
tick_init();//時(shí)鐘初始化
boot_cpu_init();//啟動(dòng)cpu初始化
page_address_init();//頁(yè)面初始化
printk(KERN_NOTICE "%s", linux_banner);
setup_arch(&command_line);//架構(gòu)相關(guān)初始化
mm_init_owner(&init_mm, &init_task);//內(nèi)存管理初始化
mm_init_cpumask(&init_mm);//內(nèi)存管理初始化
setup_command_line(command_line);//處理命令行(保存2份)
setup_nr_cpu_ids();//cpuid相關(guān)
setup_per_cpu_areas();//每cpu變量申請(qǐng)空間(包括gdt)
//smp中用來啟動(dòng)的cpu
smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
//建立系統(tǒng)內(nèi)存頁(yè)區(qū)鏈表
build_all_zonelists(NULL);
//內(nèi)存頁(yè)相關(guān)初始化
page_alloc_init();
printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line);
//命令行boot_command_line
parse_early_param();
//解析參數(shù)
parse_args("Booting kernel", static_command_line, __start___param,
__stop___param - __start___param,
-1, -1, &unknown_bootoption);
//
jump_label_init();
/*
* These use large bootmem allocations and must precede
* kmem_cache_init()
* 內(nèi)存初始化相關(guān)
*/
setup_log_buf(0);
pidhash_init();
vfs_caches_init_early();
sort_main_extable();
trap_init();
mm_init();
/*
* 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.
* 調(diào)度初始化
*/
sched_init();
/*
* Disable preemption - early bootup scheduling is extremely
* fragile until we cpu_idle() for the first time.
* 搶占禁用
*/
preempt_disable();
if (!irqs_disabled()) {
printk(KERN_WARNING "start_kernel(): bug: interrupts were "
"enabled *very* early, fixing it\n");
local_irq_disable();
}
idr_init_cache();//idr
perf_event_init();//performance event
rcu_init();//read-copy-update 機(jī)制
radix_tree_init();//radix樹機(jī)制
/* init some links before init_ISA_irqs() */
early_irq_init();//中斷請(qǐng)求
init_IRQ();//中斷請(qǐng)求
prio_tree_init();//優(yōu)先查找樹
init_timers();//時(shí)鐘
hrtimers_init();//High-resolution kernel timers高精度內(nèi)核時(shí)鐘
softirq_init();//軟中斷
timekeeping_init();//時(shí)間相關(guān)
time_init();//時(shí)間
profile_init();//分配內(nèi)核性能統(tǒng)計(jì)保存的內(nèi)存
call_function_init();//smp中每cpu的call_single_queue初始化
if (!irqs_disabled())
printk(KERN_CRIT "start_kernel(): bug: interrupts were "
"enabled early\n");
early_boot_irqs_disabled = false;//中斷請(qǐng)求開
local_irq_enable();//本地中斷開
kmem_cache_init_late();//kmem后期初始化
/*
* 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();//初始化系統(tǒng)控制臺(tái)結(jié)構(gòu)
if (panic_later)
panic(panic_later, panic_param);
//鎖依賴信息
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 &&
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();//control groups初始化
debug_objects_mem_init();//對(duì)象調(diào)試
kmemleak_init();//檢測(cè)內(nèi)核內(nèi)存泄漏的功能
setup_per_cpu_pageset();//申請(qǐng)并初始化每cpu頁(yè)set
numa_policy_init();//numa相關(guān)
if (late_time_init)
late_time_init();
//初始化每cpusched_clock_data=ktime_now
sched_clock_init();
calibrate_delay();//計(jì)算cpuMIPS百萬條指令/s
pidmap_init();//pid進(jìn)程id表初始化
anon_vma_init();//虛擬地址
#ifdef CONFIG_X86
if (efi_enabled)//efi bois
efi_enter_virtual_mode();
#endif
thread_info_cache_init();//申請(qǐng)thread_info的內(nèi)存
cred_init();//credential健在分配
//根據(jù)物理內(nèi)存大小,計(jì)算可創(chuàng)建進(jìn)/線程數(shù)量
fork_init(totalram_pages);
proc_caches_init();//進(jìn)程內(nèi)存初始化
buffer_init();//頁(yè)高速緩存
key_init();//紅黑樹內(nèi)存,存keys
security_init();//安全相關(guān)
dbg_late_init();//調(diào)試相關(guān)
vfs_caches_init(totalram_pages);//虛擬文件系統(tǒng)初始化
signals_init();//sigqueue申請(qǐng)內(nèi)存,信號(hào)系統(tǒng)
/* rootfs populating might need page-writeback */
page_writeback_init();//頁(yè)回寫
#ifdef CONFIG_PROC_FS
proc_root_init();//proc文件系統(tǒng)初始化
#endif
cgroup_init();//cgroup相關(guān)
cpuset_init();//cpuset相關(guān)
taskstats_init_early();//進(jìn)程計(jì)數(shù)器
delayacct_init();//進(jìn)程延時(shí)審計(jì)
check_bugs();//系統(tǒng)bug相關(guān)測(cè)試
//acpi總線
acpi_early_init(); /* before LAPIC and SMP init */
sfi_init_late();//Simple Firmware Interface
//功能追蹤初始化,一種調(diào)試工具
ftrace_init();
/* Do the rest non-__init'ed, we're now alive */
rest_init();
}
/* Call all constructor functions linked into the kernel. */
static void __init do_ctors(void)
{
#ifdef CONFIG_CONSTRUCTORS
ctor_fn_t *fn = (ctor_fn_t *) __ctors_start;
for (; fn < (ctor_fn_t *) __ctors_end; fn++)
(*fn)();
#endif
}
bool initcall_debug;
core_param(initcall_debug, initcall_debug, bool, 0644);
static char msgbuf[64];
static int __init_or_module do_one_initcall_debug(initcall_t fn)
{
ktime_t calltime, delta, rettime;
unsigned long long duration;
int ret;
printk(KERN_DEBUG "calling %pF @ %i\n", fn, task_pid_nr(current));
calltime = ktime_get();
ret = fn();
rettime = ktime_get();
delta = ktime_sub(rettime, calltime);
duration = (unsigned long long) ktime_to_ns(delta) >> 10;
printk(KERN_DEBUG "initcall %pF returned %d after %lld usecs\n", fn,
ret, duration);
return ret;
}
int __init_or_module do_one_initcall(initcall_t fn)
{
int count = preempt_count();
int ret;
if (initcall_debug)
ret = do_one_initcall_debug(fn);
else
ret = fn();
msgbuf[0] = 0;
if (ret && ret != -ENODEV && initcall_debug)
sprintf(msgbuf, "error code %d ", ret);
if (preempt_count() != count) {
strlcat(msgbuf, "preemption imbalance ", sizeof(msgbuf));
preempt_count() = count;
}
if (irqs_disabled()) {
strlcat(msgbuf, "disabled interrupts ", sizeof(msgbuf));
local_irq_enable();
}
if (msgbuf[0]) {
printk("initcall %pF returned with %s\n", fn, msgbuf);
}
return ret;
}
extern initcall_t __initcall_start[];
extern initcall_t __initcall0_start[];
extern initcall_t __initcall1_start[];
extern initcall_t __initcall2_start[];
extern initcall_t __initcall3_start[];
extern initcall_t __initcall4_start[];
extern initcall_t __initcall5_start[];
extern initcall_t __initcall6_start[];
extern initcall_t __initcall7_start[];
extern initcall_t __initcall_end[];
static initcall_t *initcall_levels[] __initdata = {
__initcall0_start,
__initcall1_start,
__initcall2_start,
__initcall3_start,
__initcall4_start,
__initcall5_start,
__initcall6_start,
__initcall7_start,
__initcall_end,
};
static char *initcall_level_names[] __initdata = {
"early parameters",
"core parameters",
"postcore parameters",
"arch parameters",
"subsys parameters",
"fs parameters",
"device parameters",
"late parameters",
};
static void __init do_initcall_level(int level)
{
extern const struct kernel_param __start___param[], __stop___param[];
initcall_t *fn;
strcpy(static_command_line, saved_command_line);
parse_args(initcall_level_names[level],
static_command_line, __start___param,
__stop___param - __start___param,
level, level,
repair_env_string);
for (fn = initcall_levels[level]; fn < initcall_levels[level+1]; fn++)
do_one_initcall(*fn);
}
static void __init do_initcalls(void)
{
int level;
for (level = 0; level < ARRAY_SIZE(initcall_levels) - 1; level++)
do_initcall_level(level);
}
/*
* 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();//smp cpuset相關(guān)
usermodehelper_init();//khelper單線程工作隊(duì)列
shmem_init();//sheme機(jī)制
driver_init();//驅(qū)動(dòng)各子系統(tǒng)
init_irq_proc();//proc中創(chuàng)建irq目錄
do_ctors();//內(nèi)核中所有構(gòu)造函數(shù),介于.ctors段中的函數(shù)
usermodehelper_enable();
//所有編譯進(jìn)內(nèi)核的驅(qū)動(dòng)模塊初始化函數(shù)
do_initcalls();
}
static void __init do_pre_smp_initcalls(void)
{
initcall_t *fn;
for (fn = __initcall_start; fn < __initcall0_start; fn++)
do_one_initcall(*fn);
}
static void run_init_process(const char *init_filename)
{
argv_init[0] = init_filename;
kernel_execve(init_filename, argv_init, envp_init);
}
/* This is a non __init function. Force it to be noinline otherwise gcc
* makes it inline to init() and it becomes part of init.text section
* 這是個(gè)非Init函數(shù),防止gcc讓它內(nèi)聯(lián)到init(),并成為Init.text段的一部分
*/
static noinline int init_post(void)
{
/* need to finish all async __init code before freeing the memory
* 在釋放init內(nèi)存前,必須完成所有__init代碼執(zhí)行
*/
async_synchronize_full();
free_initmem();//釋放init.*段中的內(nèi)存
//修改頁(yè)表,保證只讀數(shù)據(jù)段為只讀屬性read only
mark_rodata_ro();
//系統(tǒng)運(yùn)行狀態(tài)標(biāo)志
system_state = SYSTEM_RUNNING;
//numa默認(rèn)策略
numa_default_policy();
//當(dāng)前進(jìn)程不能被殺掉,只為它是init
current->signal->flags |= SIGNAL_UNKILLABLE;
//如果ramdisk_execute_command變量指定了init程序,執(zhí)行它
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.
* 又一個(gè)程序,看能不能執(zhí)行,如果不能,則執(zhí)行下面4個(gè)之一
*/
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");
//兩個(gè)變量和4個(gè)init都不能成功執(zhí)行,報(bào)錯(cuò)
panic("No init found. Try passing init= option to kernel. "
"See Linux Documentation/init.txt for guidance.");
}
static int __init kernel_init(void * unused)
{
/*
* Wait until kthreadd is all set-up.等待kthreadd的啟動(dòng)完成
*/
wait_for_completion(&kthreadd_done);
/* Now the scheduler is fully set up and can do blocking allocations
*
*/
gfp_allowed_mask = __GFP_BITS_MASK;
/*
* init can allocate pages on any node
*/
set_mems_allowed(node_states[N_HIGH_MEMORY]);
/*
* init can run on any cpu.
*/
set_cpus_allowed_ptr(current, cpu_all_mask);
//cad_pid為接收Ctrl-alt-del操作的INT信號(hào)的進(jìn)程ID,設(shè)置成了init的pid
//說明init可接受這3個(gè)鍵
cad_pid = task_pid(current);
//smp系統(tǒng)準(zhǔn)備、激活所有cpu
smp_prepare_cpus(setup_max_cpus);
do_pre_smp_initcalls();
lockup_detector_init();
smp_init();
sched_init_smp();
//初始化設(shè)備驅(qū)動(dòng)、內(nèi)核模塊
do_basic_setup();
/* Open the /dev/console on the rootfs, this should never fail
* 打開/dev/console設(shè)備
*/
if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
printk(KERN_WARNING "Warning: unable to open an initial console.\n");
/*
* 復(fù)制兩次標(biāo)準(zhǔn)輸入0,一個(gè)是標(biāo)準(zhǔn)輸入1,一個(gè)是標(biāo)準(zhǔn)錯(cuò)誤2
*/
(void) sys_dup(0);
(void) sys_dup(0);
/*
* check if there is an early userspace init. If yes, let it do all
* the work
* 是否有早期用戶空間init進(jìn)程,有的話,讓其執(zhí)行
*/
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..
*/
//啟動(dòng)用戶空間的init進(jìn)程
init_post();
return 0;
}
到此,相信大家對(duì)“l(fā)inux內(nèi)核是否有main函數(shù)”有了更深的了解,不妨來實(shí)際操作一番吧!這里是創(chuàng)新互聯(lián)網(wǎng)站,更多相關(guān)內(nèi)容可以進(jìn)入相關(guān)頻道進(jìn)行查詢,關(guān)注我們,繼續(xù)學(xué)習(xí)!
新聞標(biāo)題:linux內(nèi)核是否有main函數(shù)
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