Linux修改kernel log level

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Linux

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提高kernel log level有两种方法:

1、是通过bootloader传递参数给kernel,可以传递的参数为debug和quiet。分别对应CONSOLE_LOGLEVEL_DEBUG和CONSOLE_LOGLEVEL_QUIET两种level。

static int __init debug_kernel(char *str)//__init是在init.h中定义的宏,被标记的代码会放在特定section中
{
console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
return 0;
}

static int __init quiet_kernel(char *str)
{
console_loglevel = CONSOLE_LOGLEVEL_QUIET;
return 0;
}
early_param("debug", debug_kernel);
early_param("quiet", quiet_kernel);

2、通过proc文件系统修改

echo 10 4 1 7 > /proc/sys/kernel/printk

上面这条语句可以同第一种通过bootloader传递达到一样的效果。

具体实现在sysctl.c(kernel)中

{
.procname = "printk",
.data = &console_loglevel,
.maxlen = 4*sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec,
}


/**
* proc_dointvec - read a vector of integers
* @table: the sysctl table
* @write: %TRUE if this is a write to the sysctl file
* @buffer: the user buffer
* @lenp: the size of the user buffer
* @ppos: file position
*
* Reads/writes up to table->maxlen/sizeof(unsigned int) integer
* values from/to the user buffer, treated as an ASCII string.
*
* Returns 0 on success.
*/
int proc_dointvec(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
return do_proc_dointvec(table, write, buffer, lenp, ppos, NULL, NULL);
}

/**
* proc_douintvec - read a vector of unsigned integers
* @table: the sysctl table
* @write: %TRUE if this is a write to the sysctl file
* @buffer: the user buffer
* @lenp: the size of the user buffer
* @ppos: file position
*
* Reads/writes up to table->maxlen/sizeof(unsigned int) unsigned integer
* values from/to the user buffer, treated as an ASCII string.
*
* Returns 0 on success.
*/
int proc_douintvec(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
return do_proc_douintvec(table, write, buffer, lenp, ppos,
do_proc_douintvec_conv, NULL);
}

static int do_proc_douintvec_conv(unsigned long *lvalp,
unsigned int *valp,
int write, void *data)
{
if (write) {
if (*lvalp > UINT_MAX)
return -EINVAL;
*valp = *lvalp;
} else {
unsigned int val = *valp;
*lvalp = (unsigned long)val;
}
return 0;
}

这里write=1, 所以执行*valp=*lvalp

而valp指向的是console_loglevel,而lvalp就是通过echo写入的值。