Linux下printk原理

看下printk的实现

asmlinkage __visible int printk(const char *fmt, ...)
{
	r = vprintk_func(fmt, args);
}
 
__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
{
	return vprintk_default(fmt, args);
}
 
int vprintk_default(const char *fmt, va_list args)
{
	r = vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
}
 
asmlinkage int vprintk_emit(int facility, int level,const char *dict, size_t dictlen,const char *fmt, va_list args)
{
 
	console_unlock();
}
 
void console_unlock(void)
{
 
	call_console_drivers(level, text, len);
}
 
static void call_console_drivers(int level, const char *text, size_t len)
{
	struct console *con;
	
	for_each_console(con) {
		con->write(con, text, len);
	}
}

也就是调用con->write的写接口,把log输出到串口上。

那控制台什么时候注册，以sprd的为例

#define SPRD_TTY_NAME		"ttyS"
static struct console sprd_console = {
	.name = SPRD_TTY_NAME,
	.write = sprd_console_write,
	.device = uart