调整内核printk的打印级别

    有时调试内核模块，打印信息太多，可以通过修改 /proc/sys/kernel/printk文件内容来调整输出。数值越小，优先级越高。

以上四个值在kernel/printk/printk.c中定义，如下：

int console_printk[4] = {
    CONSOLE_LOGLEVEL_DEFAULT,   /* console_loglevel */
    MESSAGE_LOGLEVEL_DEFAULT,   /* default_message_loglevel */
    CONSOLE_LOGLEVEL_MIN,       /* minimum_console_loglevel */
    CONSOLE_LOGLEVEL_DEFAULT,   /* default_console_loglevel */
};

内核的日志等级：

#define KERN_EMERG      KERN_SOH "0"    /* system is unusable */
#define KERN_ALERT      KERN_SOH "1"    /* action must be taken immediately */
#define KERN_CRIT       KERN_SOH "2"    /* critical conditions */
#define KERN_ERR        KERN_SOH "3"    /* error conditions */
#define KERN_WARNING    KERN_SOH "4"    /* warning conditions */
#define KERN_NOTICE     KERN_SOH "5"    /* normal but significant condition */
#define KERN_INFO       KERN_SOH "6"    /* informational */
#define KERN_DEBUG      KERN_SOH "7"    /* debug-level messages */

#define KERN_DEFAULT    KERN_SOH "d"    /* the default kernel loglevel */

示例：手动屏蔽所有的内核printk打印。

 echo  1 4 1 7 > /proc/sys/kernel/printk