预定义的内核log等级
// include/linux/kern_levels.h
#define KERN_SOH "\001" /* ASCII Start Of Header */
#define KERN_SOH_ASCII '\001'
#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 */
printk打印消息控制
// linux/include/printk.h
/* printk's without a loglevel use this.. */
#define MESSAGE_LOGLEVEL_DEFAULT CONFIG_MESSAGE_LOGLEVEL_DEFAULT
/* We show everything that is MORE important than this.. */
#define CONSOLE_LOGLEVEL_DEFAULT 7
#define CONSOLE_LOGLEVEL_MIN 1
#define CONSOLE_LOGLEVEL_DEFAULT 7
--------------------------------------------------------
// kernel/printk.c
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 */
};
--------------------------------------------------------
// linux/include/printk.h
extern int console_printk[];
#define console_loglevel (console_printk[0])
#define default_message_loglevel (console_printk[1])
#define minimum_console_loglevel (console_printk[2])
#define default_console_loglevel (console_printk[3])
1.console_loglevel
只有当printk打印消息的log优先级高于console_loglevel时，才能输出到终端上
2.default_message_loglevel
printk打印消息时默认的log等级
3.minimum_console_loglevel
console_loglevel可以被设置的最小值
4.default_console_loglevel
console_loglevel的缺省值
通过procfs控制printk打印消息
1.查看当前printk打印消息的log等级
# cat /proc/sys/kernel/printk
# 7 4 1 7
“7 4 1 7” 分别对应console_loglevel、default_message_loglevel、minimum_c onsole_loglevel、default_console_loglevel，意味着只有优先级高于KERN_DEBUG(7)的打印消息才能输出到终端
2.改变console_loglevel
# echo 8 4 1 7 > /proc/sys/kernel/printk
输入“8 4 1 7”改变console_loglevel值，使得所有的打印消息都能输出到终端
3.procfs系列节点
static struct ctl_table kern_table[] = {
......
#if defined CONFIG_PRINTK
{
.procname = "printk",
.data = &console_loglevel,
.maxlen = 4*sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec,
},
{
.procname = "printk_ratelimit",
.data = &printk_ratelimit_state.interval,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_jiffies,
},
{
.procname = "printk_ratelimit_burst",
.data = &printk_ratelimit_state.burst,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec,
},
{
.procname = "printk_delay",
.data = &printk_delay_msec,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
.extra1 = &zero,
.extra2 = &ten_thousand,
},
{
.procname = "printk_devkmsg",
.data = devkmsg_log_str,
.maxlen = DEVKMSG_STR_MAX_SIZE,
.mode = 0644,
.proc_handler = devkmsg_sysctl_set_loglvl,
},
{
.procname = "dmesg_restrict",
.data = &dmesg_restrict,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax_sysadmin,
.extra1 = &zero,
.extra2 = &one,
},
{
.procname = "kptr_restrict",
.data = &kptr_restrict,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax_sysadmin,
.extra1 = &zero,
.extra2 = &two,
},
#endif
......
{ }
};