printk.c

来自「一份精简的linux内核源代码」· C语言 代码 · 共 42 行

/*
 *  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, ...)/*打印函数(仅仅设了一下FS的值，实际打印操作由tty_write完成)*/
{
	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"/*打印长度*/
		"pushl $_buf\n\t"/*打印的内容*/
		"pushl $0\n\t"/*通道0*/
		"call _tty_write\n\t"/*实际的打印操作*/
		"addl $8,%%esp\n\t"
		"popl %0\n\t"
		"pop %%fs"
		::"r" (i):"ax","cx","dx");
	return i;
}