kernel源码（十六）vsprintf.c和printk.c和panic.c
这两个源码用于对参数产生格式化输出，和内核关系不大，主要是调用C语言进行一些格式化操作。了解一下。
1 vsprintf.c源码
/* * linux/kernel/vsprintf.c * * (C) 1991 Linus Torvalds */ /* vsprintf.c -- Lars Wirzenius & Linus Torvalds. */ /* * Wirzenius wrote this portably, Torvalds fucked it up :-) */ #include <stdarg.h> #include <string.h> /* we use this so that we can do without the ctype library */ #define is_digit(c) ((c) >= '0' && (c) <= '9') static int skip_atoi(const char **s) { int i=0; while (is_digit(**s)) i = i*10 + *((*s)++) - '0'; return i; } #define ZEROPAD 1 /* pad with zero */ #define SIGN 2 /* unsigned/signed long */ #define PLUS 4 /* show plus */ #define SPACE 8 /* space if plus */ #define LEFT 16 /* left justified */ #define SPECIAL 32 /* 0x */ #define SMALL 64 /* use 'abcdef' instead of 'ABCDEF' */ #define do_div(n,base) ({ \ int __res; \ __asm__("divl %4":"=a" (n),"=d" (__res):"0" (n),"1" (0),"r" (base)); \ __res; }) static char * number(char * str, int num, int base, int size, int precision ,int type) { char c,sign,tmp[36]; const char *digits="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; int i; if (type&SMALL) digits="0123456789abcdefghijklmnopqrstuvwxyz"; if (type&LEFT) type &= ~ZEROPAD; if (base<2 || base>36) return 0; c = (type & ZEROPAD) ? '0' : ' ' ; if (type&SIGN && num<0) { sign='-'; num = -num; } else sign=(type&PLUS) ? '+' : ((type&SPACE) ? ' ' : 0); if (sign) size--; if (type&SPECIAL) if (base==16) size -= 2; else if (base==8) size--; i=0; if (num==0) tmp[i++]='0'; else while (num!=0) tmp[i++]=digits[do_div(num,base)]; if (i>precision) precision=i; size -= precision; if (!(type&(ZEROPAD+LEFT))) while(size-->0) *str++ = ' '; if (sign) *str++ = sign; if (type&SPECIAL) if (base==8) *str++ = '0'; else if (base==16) { *str++ = '0'; *str++ = digits[33]; } if (!(type&LEFT)) while(size-->0) *str++ = c; while(i<precision--) *str++ = '0'; while(i-->0) *str++ = tmp[i]; while(size-->0) *str++ = ' '; return str; } int vsprintf(char *buf, const char *fmt, va_list args) { int len; int i; char * str; char *s; int *ip; int flags; /* flags to number() */ int field_width; /* width of output field */ int precision; /* min. # of digits for integers; max number of chars for from string */ int qualifier; /* 'h', 'l', or 'L' for integer fields */ for (str=buf ; *fmt ; ++fmt) { if (*fmt != '%') { *str++ = *fmt; continue; } /* process flags */ flags = 0; repeat: ++fmt; /* this also skips first '%' */ switch (*fmt) { case '-': flags |= LEFT; goto repeat; case '+': flags |= PLUS; goto repeat; case ' ': flags |= SPACE; goto repeat; case '#': flags |= SPECIAL; goto repeat; case '0': flags |= ZEROPAD; goto repeat; } /* get field width */ field_width = -1; if (is_digit(*fmt)) field_width = skip_atoi(&fmt); else if (*fmt == '*') { /* it's the next argument */ field_width = va_arg(args, int); if (field_width < 0) { field_width = -field_width; flags |= LEFT; } } /* get the precision */ precision = -1; if (*fmt == '.') { ++fmt; if (is_digit(*fmt)) precision = skip_atoi(&fmt); else if (*fmt == '*') { /* it's the next argument */ precision = va_arg(args, int); } if (precision < 0) precision = 0; } /* get the conversion qualifier */ qualifier = -1; if (*fmt == 'h' || *fmt == 'l' || *fmt == 'L') { qualifier = *fmt; ++fmt; } switch (*fmt) { case 'c': if (!(flags & LEFT)) while (--field_width > 0) *str++ = ' '; *str++ = (unsigned char) va_arg(args, int); while (--field_width > 0) *str++ = ' '; break; case 's': s = va_arg(args, char *); len = strlen(s); if (precision < 0) precision = len; else if (len > precision) len = precision; if (!(flags & LEFT)) while (len < field_width--) *str++ = ' '; for (i = 0; i < len; ++i) *str++ = *s++; while (len < field_width--) *str++ = ' '; break; case 'o': str = number(str, va_arg(args, unsigned long), 8, field_width, precision, flags); break; case 'p': if (field_width == -1) { field_width = 8; flags |= ZEROPAD; } str = number(str, (unsigned long) va_arg(args, void *), 16, field_width, precision, flags); break; case 'x': flags |= SMALL; case 'X': str = number(str, va_arg(args, unsigned long), 16, field_width, precision, flags); break; case 'd': case 'i': flags |= SIGN; case 'u': str = number(str, va_arg(args, unsigned long), 10, field_width, precision, flags); break; case 'n': ip = va_arg(args, int *); *ip = (str - buf); break; default: if (*fmt != '%') *str++ = '%'; if (*fmt) *str++ = *fmt; else --fmt; break; } } *str = '\0'; return str-buf; }
把数字串转成整数
static int skip_atoi(const char **s) { int i=0; while (is_digit(**s)) i = i*10 + *((*s)++) - '0'; return i; }
把整数转换为二进制的字符串
static char * number(char * str, int num, int base, int size, int precision ,int type) { char c,sign,tmp[36]; const char *digits="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; int i; if (type&SMALL) digits="0123456789abcdefghijklmnopqrstuvwxyz"; if (type&LEFT) type &= ~ZEROPAD; if (base<2 || base>36) return 0; c = (type & ZEROPAD) ? '0' : ' ' ; if (type&SIGN && num<0) { sign='-'; num = -num; } else sign=(type&PLUS) ? '+' : ((type&SPACE) ? ' ' : 0); if (sign) size--; if (type&SPECIAL) if (base==16) size -= 2; else if (base==8) size--; i=0; if (num==0) tmp[i++]='0'; else while (num!=0) tmp[i++]=digits[do_div(num,base)]; if (i>precision) precision=i; size -= precision; if (!(type&(ZEROPAD+LEFT))) while(size-->0) *str++ = ' '; if (sign) *str++ = sign; if (type&SPECIAL) if (base==8) *str++ = '0'; else if (base==16) { *str++ = '0'; *str++ = digits[33]; } if (!(type&LEFT)) while(size-->0) *str++ = c; while(i<precision--) *str++ = '0'; while(i-->0) *str++ = tmp[i]; while(size-->0) *str++ = ' '; return str; }
格式化输出
int vsprintf(char *buf, const char *fmt, va_list args) { int len; int i; char * str; char *s; int *ip; int flags; /* flags to number() */ int field_width; /* width of output field */ int precision; /* min. # of digits for integers; max number of chars for from string */ int qualifier; /* 'h', 'l', or 'L' for integer fields */ for (str=buf ; *fmt ; ++fmt) { if (*fmt != '%') { *str++ = *fmt; continue; } /* process flags */ flags = 0; repeat: ++fmt; /* this also skips first '%' */ switch (*fmt) { case '-': flags |= LEFT; goto repeat; case '+': flags |= PLUS; goto repeat; case ' ': flags |= SPACE; goto repeat; case '#': flags |= SPECIAL; goto repeat; case '0': flags |= ZEROPAD; goto repeat; } /* get field width */ field_width = -1; if (is_digit(*fmt)) field_width = skip_atoi(&fmt); else if (*fmt == '*') { /* it's the next argument */ field_width = va_arg(args, int); if (field_width < 0) { field_width = -field_width; flags |= LEFT; } } /* get the precision */ precision = -1; if (*fmt == '.') { ++fmt; if (is_digit(*fmt)) precision = skip_atoi(&fmt); else if (*fmt == '*') { /* it's the next argument */ precision = va_arg(args, int); } if (precision < 0) precision = 0; } /* get the conversion qualifier */ qualifier = -1; if (*fmt == 'h' || *fmt == 'l' || *fmt == 'L') { qualifier = *fmt; ++fmt; } switch (*fmt) { case 'c': if (!(flags & LEFT)) while (--field_width > 0) *str++ = ' '; *str++ = (unsigned char) va_arg(args, int); while (--field_width > 0) *str++ = ' '; break; case 's': s = va_arg(args, char *); len = strlen(s); if (precision < 0) precision = len; else if (len > precision) len = precision; if (!(flags & LEFT)) while (len < field_width--) *str++ = ' '; for (i = 0; i < len; ++i) *str++ = *s++; while (len < field_width--) *str++ = ' '; break; case 'o': str = number(str, va_arg(args, unsigned long), 8, field_width, precision, flags); break; case 'p': if (field_width == -1) { field_width = 8; flags |= ZEROPAD; } str = number(str, (unsigned long) va_arg(args, void *), 16, field_width, precision, flags); break; case 'x': flags |= SMALL; case 'X': str = number(str, va_arg(args, unsigned long), 16, field_width, precision, flags); break; case 'd': case 'i': flags |= SIGN; case 'u': str = number(str, va_arg(args, unsigned long), 10, field_width, precision, flags); break; case 'n': ip = va_arg(args, int *); *ip = (str - buf); break; default: if (*fmt != '%') *str++ = '%'; if (*fmt) *str++ = *fmt; else --fmt; break; } } *str = '\0'; return str-buf; }
2 printk.c
/* * linux/kernel/printk.c * * (C) 1991 Linus Torvalds */ /* * When in kernel-mode, we cannot use printf, as fs is liable to * point to 'interesting' things. Make a printf with fs-saving, and * all is well. */ #include <stdarg.h> #include <stddef.h> #include <linux/kernel.h> static char buf[1024]; extern int vsprintf(char * buf, const char * fmt, va_list args); int printk(const char *fmt, ...) { va_list args; int i; va_start(args, fmt); i=vsprintf(buf,fmt,args); va_end(args); __asm__("push %%fs\n\t" "push %%ds\n\t" "pop %%fs\n\t" "pushl %0\n\t" "pushl $_buf\n\t" "pushl $0\n\t" "call _tty_write\n\t" "addl $8,%%esp\n\t" "popl %0\n\t" "pop %%fs" ::"r" (i):"ax","cx","dx"); return i; }
3 panic.c
在内核出现很严重错误的时候，用于打印内核错误信息，并进入死循环
#include <linux/kernel.h> #include <linux/sched.h> void sys_sync(void); /* it's really int */ volatile void panic(const char * s) { printk("Kernel panic: %s\n\r",s); if (current == task[0]) printk("In swapper task - not syncing\n\r"); else sys_sync(); for(;;); }
