init/main.c

/*
* linux/init/main.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*/

#include <stdarg.h>

#include <asm/system.h>
#include <asm/io.h>

#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/config.h>
#include <linux/sched.h>
#include <linux/tty.h>
#include <linux/head.h>
#include <linux/unistd.h>
#include <linux/string.h>
#include <linux/timer.h>
#include <linux/fs.h>
#include <linux/ctype.h>
#include <linux/delay.h>
#include <linux/utsname.h>
#include <linux/ioport.h>

extern unsigned long * prof_buffer;
extern unsigned long prof_len;
extern char edata, end;
extern char *linux_banner;
//此函数在sys_call.s文件中
asmlinkage void lcall7(void);
struct desc_struct default_ldt;

/*
* we need this inline - forking from kernel space will result
* in NO COPY ON WRITE (!!!), until an execve is executed. This
* is no problem, but for the stack. This is handled by not letting
* main() use the stack at all after fork(). Thus, no function
* calls - which means inline code for fork too, as otherwise we
* would use the stack upon exit from 'fork()'.
*
* Actually only pause and fork are needed inline, so that there
* won't be any messing with the stack from main(), but we define
* some others too.
*/
#define __NR__exit __NR_exit
static inline _syscall0(int,idle)
static inline _syscall0(int,fork)
static inline _syscall0(int,pause)
static inline _syscall1(int,setup,void *,BIOS)
static inline _syscall0(int,sync)
static inline _syscall0(pid_t,setsid)
static inline _syscall3(int,write,int,fd,const char *,buf,off_t,count)
static inline _syscall1(int,dup,int,fd)
static inline _syscall3(int,execve,const char *,file,char **,argv,char **,envp)
static inline _syscall3(int,open,const char *,file,int,flag,int,mode)
static inline _syscall1(int,close,int,fd)
static inline _syscall1(int,_exit,int,exitcode)
static inline _syscall3(pid_t,waitpid,pid_t,pid,int *,wait_stat,int,options)

static inline pid_t wait(int * wait_stat)
{
return waitpid(-1,wait_stat,0);
}

static char printbuf[1024];

//控制台日志级别
extern int console_loglevel;

//零页
extern char empty_zero_page[PAGE_SIZE];
extern int vsprintf(char *,const char *,va_list);
extern void init(void);
extern void init_IRQ(void);
extern long kmalloc_init (long,long);
extern long blk_dev_init(long,long);
extern long chr_dev_init(long,long);
extern void floppy_init(void);
extern void sock_init(void);
extern long rd_init(long mem_start, int length);
unsigned long net_dev_init(unsigned long, unsigned long);
extern unsigned long simple_strtoul(const char *,char **,unsigned int);

extern void hd_setup(char *str, int *ints);
extern void bmouse_setup(char *str, int *ints);
extern void eth_setup(char *str, int *ints);
extern void xd_setup(char *str, int *ints);
extern void mcd_setup(char *str, int *ints);
extern void st0x_setup(char *str, int *ints);
extern void tmc8xx_setup(char *str, int *ints);
extern void t128_setup(char *str, int *ints);
extern void generic_NCR5380_setup(char *str, int *intr);
extern void aha152x_setup(char *str, int *ints);
extern void sound_setup(char *str, int *ints);
#ifdef CONFIG_SBPCD
extern void sbpcd_setup(char *str, int *ints);
#endif CONFIG_SBPCD

#ifdef CONFIG_SYSVIPC
extern void ipc_init(void);
#endif
#ifdef CONFIG_SCSI
extern unsigned long scsi_dev_init(unsigned long, unsigned long);
#endif

/*
* This is set up by the setup-routine at boot-time
*/
#define PARAM empty_zero_page
#define EXT_MEM_K (*(unsigned short *) (PARAM+2))
#define DRIVE_INFO (*(struct drive_info_struct *) (PARAM+0x80))
#define SCREEN_INFO (*(struct screen_info *) (PARAM+0))
#define MOUNT_ROOT_RDONLY (*(unsigned short *) (PARAM+0x1F2))
#define RAMDISK_SIZE (*(unsigned short *) (PARAM+0x1F8))
#define ORIG_ROOT_DEV (*(unsigned short *) (PARAM+0x1FC))
#define AUX_DEVICE_INFO (*(unsigned char *) (PARAM+0x1FF))

/*
* Boot command-line arguments
*/
#define MAX_INIT_ARGS 8
#define MAX_INIT_ENVS 8
#define COMMAND_LINE ((char *) (PARAM+2048))

extern void time_init(void);

static unsigned long memory_start = 0; /* After mem_init, stores the */
/* amount of free user memory */
static unsigned long memory_end = 0;
static unsigned long low_memory_start = 0;

static char term[21];
int rows, cols;

static char * argv_init[MAX_INIT_ARGS+2] = { "init", NULL, };
static char * envp_init[MAX_INIT_ENVS+2] = { "HOME=/", term, NULL, };

static char * argv_rc[] = { "/bin/sh", NULL };
static char * envp_rc[] = { "HOME=/", term, NULL };

static char * argv[] = { "-/bin/sh",NULL };
static char * envp[] = { "HOME=/usr/root", term, NULL };

struct drive_info_struct { char dummy[32]; } drive_info;
struct screen_info screen_info;

unsigned char aux_device_present;
int ramdisk_size;
int root_mountflags = 0;

static char fpu_error = 0;

static char command_line[80] = { 0, };

char *get_options(char *str, int *ints)
{
char *cur = str;
int i=1;

while (cur && isdigit(*cur) && i <= 10) {
ints[i++] = simple_strtoul(cur,NULL,0);
if ((cur = strchr(cur,',')) != NULL)
cur++;
}
ints[0] = i-1;
return(cur);
}

struct {
char *str;
void (*setup_func)(char *, int *);
} bootsetups[] = {
{ "reserve=", reserve_setup },
#ifdef CONFIG_INET
{ "ether=", eth_setup },
#endif
#ifdef CONFIG_BLK_DEV_HD
{ "hd=", hd_setup },
#endif
#ifdef CONFIG_BUSMOUSE
{ "bmouse=", bmouse_setup },
#endif
#ifdef CONFIG_SCSI_SEAGATE
{ "st0x=", st0x_setup },
{ "tmc8xx=", tmc8xx_setup },
#endif
#ifdef CONFIG_SCSI_T128
{ "t128=", t128_setup },
#endif
#ifdef CONFIG_SCSI_GENERIC_NCR5380
{ "ncr5380=", generic_NCR5380_setup },
#endif
#ifdef CONFIG_SCSI_AHA152X
{ "aha152x=", aha152x_setup},
#endif
#ifdef CONFIG_BLK_DEV_XD
{ "xd=", xd_setup },
#endif
#ifdef CONFIG_MCD
{ "mcd=", mcd_setup },
#endif
#ifdef CONFIG_SOUND
{ "sound=", sound_setup },
#endif
#ifdef CONFIG_SBPCD
{ "sbpcd=", sbpcd_setup },
#endif CONFIG_SBPCD
{ 0, 0 }
};

//检测设置,根据命令行中的命令，调整设置，实际上是设置各种设备的初始化函数
int checksetup(char *line)
{
int i = 0;
int ints[11];

//遍历数组
while (bootsetups[i].str) {
//所遍历到的项的字符串长度
int n = strlen(bootsetups[i].str);
//和给定的内容进行比较
if (!strncmp(line,bootsetups[i].str,n)) {
//如果相同，则调整挂接的设置函数
bootsetups[i].setup_func(get_options(line+n,ints), ints);
return(0);
}
i++;
}
return(1);
}

unsigned long loops_per_sec = 1;
//延迟校准
static void calibrate_delay(void)
{
int ticks;

printk("Calibrating delay loop.. ");
while (loops_per_sec <<= 1) {
ticks = jiffies;
__delay(loops_per_sec);
ticks = jiffies - ticks;
if (ticks >= HZ) {
__asm__("mull %1 ; divl %2"
:"=a" (loops_per_sec)
:"d" (HZ),
"r" (ticks),
"0" (loops_per_sec)
:"dx");
printk("ok - %lu.%02lu BogoMips\n",
loops_per_sec/500000,
(loops_per_sec/5000) % 100);
return;
}
}
printk("failed\n");
}

/*
* This is a simple kernel command line parsing function: it parses
* the command line, and fills in the arguments/environment to init
* as appropriate. Any cmd-line option is taken to be an environment
* variable if it contains the character '='.
*
*
* This routine also checks for options meant for the kernel - currently
* only the "root=XXXX" option is recognized. These options are not given
* to init - they are for internal kernel use only.
*/
//这是一个简单的内核命令行解析函数。它解析命令行参数，并且正确的填入init参数环境
static void parse_options(char *line)
{
char *next;
char *devnames[] = { "hda", "hdb", "sda", "sdb", "sdc", "sdd", "sde", "fd", "xda", "xdb", NULL };
int devnums[] = { 0x300, 0x340, 0x800, 0x810, 0x820, 0x830, 0x840, 0x200, 0xC00, 0xC40, 0};
int args, envs;

//校验参数
if (!*line)
return;
//
args = 0;
//终端默认设置为控制台模式
envs = 1; /* TERM is set to 'console' by default */
//next指向输入参数开始抵制
next = line;
//一直解析参数到结尾,分别确定根设备号、读写属性、日志级别，数学协处理器
while ((line = next) != NULL) {
//查找line字符串中的空格，将该位置置0
if ((next = strchr(line,' ')) != NULL)
*next++ = 0;
/*
* check for kernel options first..
*/
//检测内核选项

//首先检测是否有root
if (!strncmp(line,"root=",5)) {
//如果有root
int n;
line += 5;
//是否以"/dev/"开始
if (strncmp(line,"/dev/",5)) {
//如果不是，则直接将字符按16进制转换，作为根设备号
ROOT_DEV = simple_strtoul(line,NULL,16);
continue;
}
//跳过"/dev/"
line += 5;
//
for (n = 0 ; devnames[n] ; n++) {
//设备名称的长度
int len = strlen(devnames[n]);
//查找设备名称
if (!strncmp(line,devnames[n],len)) {
//确定根设备号
ROOT_DEV = devnums[n]+simple_strtoul(line+len,NULL,16);
break;
}
}
} else if (!strcmp(line,"ro")) //如果不是root，则比较是否为ro，即只读
root_mountflags |= MS_RDONLY;
else if (!strcmp(line,"rw")) //是否为rw，即读写
root_mountflags &= ~MS_RDONLY;
else if (!strcmp(line,"debug")) //日志级别
console_loglevel = 10;
else if (!strcmp(line,"no387")) { //是否定义了协处理器
hard_math = 0;
__asm__("movl %%cr0,%%eax\n\t"
"orl $0xE,%%eax\n\t"
"movl %%eax,%%cr0\n\t" : : : "ax");
} else
checksetup(line); //检测设置，重新设置函数
/*
* Then check if it's an environment variable or
* an option.
*/
//检测其它设置
if (strchr(line,'=')) {
if (envs >= MAX_INIT_ENVS)
break;
envp_init[++envs] = line;
} else {
if (args >= MAX_INIT_ARGS)
break;
argv_init[++args] = line;
}
}
argv_init[args+1] = NULL;
envp_init[envs+1] = NULL;
}

//如果在命令行中定义了内存的大小的处理方法，将from内容拷贝到to中，不包含内存的大小
static void copy_options(char * to, char * from)
{
//初始化字符变量未空格
char c = ' ';

//循环处理字符串from，搜索mem=字符串，找到定义值
do {
if (c == ' ' && !memcmp("mem=", from, 4))
memory_end = simple_strtoul(from+4, &from, 0);
c = *(to++) = *(from++);
} while (c);
}

//超时处理
static void copro_timeout(void)
{
fpu_error = 1;
timer_table[COPRO_TIMER].expires = jiffies+100;
timer_active |= 1<<COPRO_TIMER;
printk("387 failed: trying to reset\n");
send_sig(SIGFPE, last_task_used_math, 1);
outb_p(0,0xf1);
outb_p(0,0xf0);
}

//入口函数
asmlinkage void start_kernel(void)
{
/*
* Interrupts are still disabled. Do necessary setups, then
* enable them
*/
//挂接lcall7到默认的ldt中
set_call_gate(&default_ldt,lcall7);
//初始的根设备
ROOT_DEV = ORIG_ROOT_DEV;
//驱动器信息
drive_info = DRIVE_INFO;
//屏幕信息
screen_info = SCREEN_INFO;
//辅助设备信息
aux_device_present = AUX_DEVICE_INFO;
//内存结束位置 1M位置 + 扩展内存（k）*1024
memory_end = (1<<20) + (EXT_MEM_K<<10);
//忽略不到4kb大小的内存
memory_end &= PAGE_MASK;
//ramdisk的长度
ramdisk_size = RAMDISK_SIZE;
//拷贝命令行选项，实际上就是看命令行中是否指定内存大小
// 输入参数command_line目前只有空间，COMMAND_LINE为启动参数
copy_options(command_line,COMMAND_LINE);
//内存定义超过16M的处理
#ifdef CONFIG_MAX_16M
if (memory_end > 16*1024*1024)
memory_end = 16*1024*1024;
#endif
//挂接只读根设备的标志
if (MOUNT_ROOT_RDONLY)
root_mountflags |= MS_RDONLY;
//如果内核所占内存超过1M
if ((unsigned long)&end >= (1024*1024)) {
//重新按照实际情况设置核心内存的开始位置
memory_start = (unsigned long) &end;
low_memory_start = PAGE_SIZE;
} else {
//否者设置主存开始处为1M内存处
memory_start = 1024*1024;
low_memory_start = (unsigned long) &end;
}
//这里如此设置，是因为没有超过的话，在1m内存之前还有剩余

//内存低地址开始处对齐
low_memory_start = PAGE_ALIGN(low_memory_start);
//初始内存页
memory_start = paging_init(memory_start,memory_end);

//判断是否为EISA总线
if (strncmp((char*)0x0FFFD9, "EISA", 4) == 0)
EISA_bus = 1;
//初始化陷阱门
trap_init();
//初始化IRQ
init_IRQ();
//任务调度初始化
sched_init();
//解析命令行
parse_options(command_line);
//配置CONFIG_PROFILE的情况下，内存布局
#ifdef CONFIG_PROFILE
prof_buffer = (unsigned long *) memory_start;
prof_len = (unsigned long) &end;
prof_len >>= 2;
memory_start += prof_len * sizeof(unsigned long);
#endif
//初始化lmalloc
memory_start = kmalloc_init(memory_start,memory_end);
//初始化字符设备
memory_start = chr_dev_init(memory_start,memory_end);
//初始化块设备
memory_start = blk_dev_init(memory_start,memory_end);
//开中断
sti();
//延迟
calibrate_delay();
//初始化网络设备
#ifdef CONFIG_INET
memory_start = net_dev_init(memory_start,memory_end);
#endif
//初始化scsi设备
#ifdef CONFIG_SCSI
memory_start = scsi_dev_init(memory_start,memory_end);
#endif
//初始化inode
memory_start = inode_init(memory_start,memory_end);
//初始化文件表
memory_start = file_table_init(memory_start,memory_end);
//内存初始化
mem_init(low_memory_start,memory_start,memory_end);
//高速缓冲区初始化
buffer_init();
//初始化时间
time_init();
//初始化软盘
floppy_init();
//初始化sock
sock_init();
//初始化ipc
#ifdef CONFIG_SYSVIPC
ipc_init();
#endif
sti();

/*
* check if exception 16 works correctly.. This is truly evil
* code: it disables the high 8 interrupts to make sure that
* the irq13 doesn't happen. But as this will lead to a lockup
* if no exception16 arrives, it depends on the fact that the
* high 8 interrupts will be re-enabled by the next timer tick.
* So the irq13 will happen eventually, but the exception 16
* should get there first..
*/
//数学协处理器处理
if (hard_math) {
unsigned short control_word;

printk("Checking 386/387 coupling... ");
timer_table[COPRO_TIMER].expires = jiffies+50;
timer_table[COPRO_TIMER].fn = copro_timeout;
timer_active |= 1<<COPRO_TIMER;
__asm__("clts ; fninit ; fnstcw %0 ; fwait":"=m" (*&control_word));
control_word &= 0xffc0;
__asm__("fldcw %0 ; fwait": :"m" (*&control_word));
outb_p(inb_p(0x21) | (1 << 2), 0x21);
__asm__("fldz ; fld1 ; fdiv %st,%st(1) ; fwait");
timer_active &= ~(1<<COPRO_TIMER);
if (!fpu_error)
printk("Ok, fpu using %s error reporting.\n",
ignore_irq13?"exception 16":"irq13");
}
#ifndef CONFIG_MATH_EMULATION
else {
printk("No coprocessor found and no math emulation present.\n");
printk("Giving up.\n");
for (;;) ;
}
#endif

//
system_utsname.machine[1] = '0' + x86;
printk(linux_banner);

//转到用户空间
move_to_user_mode();
//创建新进程
if (!fork()) /* we count on this going ok */
//init进程
init();
/*
* task[0] is meant to be used as an "idle" task: it may not sleep, but
* it might do some general things like count free pages or it could be
* used to implement a reasonable LRU algorithm for the paging routines:
* anything that can be useful, but shouldn't take time from the real
* processes.
*
* Right now task[0] just does a infinite idle loop.
*/
for(;;)
idle();
}

//打印函数
static int printf(const char *fmt, ...)
{
va_list args;
int i;

va_start(args, fmt);
write(1,printbuf,i=vsprintf(printbuf, fmt, args));
va_end(args);
return i;
}

//init进程
void init(void)
{
int pid,i;

setup((void *) &drive_info);
sprintf(term, "TERM=con%dx%d", ORIG_VIDEO_COLS, ORIG_VIDEO_LINES);
(void) open("/dev/tty1",O_RDWR,0);
(void) dup(0);
(void) dup(0);

execve("/etc/init",argv_init,envp_init);
execve("/bin/init",argv_init,envp_init);
execve("/sbin/init",argv_init,envp_init);
/* if this fails, fall through to original stuff */

if (!(pid=fork())) {
close(0);
if (open("/etc/rc",O_RDONLY,0))
_exit(1);
execve("/bin/sh",argv_rc,envp_rc);
_exit(2);
}
if (pid>0)
while (pid != wait(&i))
/* nothing */;
while (1) {
if ((pid = fork()) < 0) {
printf("Fork failed in init\n\r");
continue;
}
if (!pid) {
close(0);close(1);close(2);
setsid();
(void) open("/dev/tty1",O_RDWR,0);
(void) dup(0);
(void) dup(0);
_exit(execve("/bin/sh",argv,envp));
}
while (1)
if (pid == wait(&i))
break;
printf("\n\rchild %d died with code %04x\n\r",pid,i);
sync();
}
_exit(0);
}