Linux 内核原代码 init/main 的注释
| define __LIBRARY__ #include #include /* * 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. */ static inline _syscall0(int,fork) @@定义fork --sys_fork在unistd.h中定义syscall0 static inline _syscall0(int,pause) static inline _syscall0(int,setup) static inline _syscall0(int,sync) #include #include #include #include #include #include #include #include #include #include #include static char printbuf[1024]; extern int vsprintf(); extern void init(void); extern void hd_init(void); extern long kernel_mktime(struct tm * tm); extern long startup_time; /* * Yeah, yeah, it's ugly, but I cannot find how to do this correctly * and this seems to work. I anybody has more info on the real-time * clock I'd be interested. Most of this was trial and error, and some * bios-listing reading. Urghh. */ #define CMOS_READ(addr) ({ outb_p(0x80|addr,0x70); inb_p(0x71); }) #define BCD_TO_BIN(val) ((val)=((val)&15) + ((val)>>4)*10) static void time_init(void) { struct tm time; do { time.tm_sec = CMOS_READ(0); time.tm_min = CMOS_READ(2); time.tm_hour = CMOS_READ(4); time.tm_mday = CMOS_READ(7); time.tm_mon = CMOS_READ(8)-1; time.tm_year = CMOS_READ(9); } while (time.tm_sec != CMOS_READ(0)); BCD_TO_BIN(time.tm_sec); BCD_TO_BIN(time.tm_min); BCD_TO_BIN(time.tm_hour); BCD_TO_BIN(time.tm_mday); BCD_TO_BIN(time.tm_mon); BCD_TO_BIN(time.tm_year); startup_time = kernel_mktime(&time); } void main(void) /* This really IS void, no error here. */ { /* The startup routine assumes (well, ...) this */ /* * Interrupts are still disabled. Do necessary setups, then * enable them */ time_init(); tty_init(); trap_init(); sched_init(); buffer_init(); hd_init(); sti(); move_to_user_mode(); @@切至用户模式???到哪去了,回来了!!! if (!fork()) { /* we count on this going ok */ init(); @@fork在unistd.h有其宏扩展int 0x80 如何返回两次?应该说子进程如何激活? } /* * NOTE!! For any other task 'pause()' would mean we have to get a * signal to awaken, but task0 is the sole exception (see 'schedule()') * as task 0 gets activated at every idle moment (when no other tasks * can run). For task0 'pause()' just means we go check if some other * task can run, and if not we return here. */ for(;;) pause(); @@pause 同fork在unistd.h有其宏扩展int 0x80 然后调schedule() } 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; } static char * argv[] = { "-",NULL }; static char * envp[] = { "HOME=/usr/root", NULL }; void init(void) { int i,j; setup(); @@系统0号调用 if (!fork()) _exit(execve("/bin/update",NULL,NULL)); (void) open("/dev/tty0",O_RDWR,0); @@打开控制台 (void) dup(0); @@复制 (void) dup(0); printf("%d buffers = %d bytes buffer spacenr",NR_BUFFERS, NR_BUFFERS*BLOCK_SIZE); printf(" Ok.nr"); if ((i=fork())<0) printf("Fork failed in initrn"); else if (!i) { @@启动一root shell进程? close(0);close(1);close(2); setsid(); (void) open("/dev/tty0",O_RDWR,0); (void) dup(0); (void) dup(0); _exit(execve("/bin/sh",argv,envp)); } j=wait(&i); printf("child %d died with code %04xn",j,i); sync(); _exit(0); /* NOTE! _exit, not exit() */ }
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