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@time-river

time-river/Makefile

Created Dec 5, 2020
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Linux lernel log level test
obj-m += printk_device.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
#define DEBUG
#define pr_fmt(fmt) "printk_device: " fmt
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
#include <linux/printk.h>
#define print(level) \
printk(level "It is '" #level "' message generated from `printk`.")
static ssize_t printk_read(struct file *file, char __user *buf,
size_t count, loff_t *off) {
pr_devel("This message is output because of macro 'DEBUG' defination.\n");
pr_debug("This message is dynamic output.\n");
pr_info_once("This message should only appear once.\n");
print(KERN_EMERG);
print(KERN_ALERT);
print(KERN_CRIT);
print(KERN_ERR);
print(KERN_WARNING);
print(KERN_NOTICE);
print(KERN_INFO);
print(KERN_DEBUG);
printk(KERN_CONT " It is the first 'KERN_CONT' message generated" \
" from printk, shouldn't start at newline.\n");
printk(KERN_CONT "It is the second 'KERN_CONT' message generated" \
" from printk, it should be at newline and appear immediately" \
" because of the end character '\\n'.\n");
printk(KERN_CONT "It is the third 'KERN_CONT' message generated" \
" from printk, it starts at newline because of the '\\n'." \
" in the end of the last 'KERN_CONT' line, but it appears" \
" in the next action because of no '\\n' suffix.");
return 0;
}
static ssize_t printk_write(struct file *file, const char __user *buf,
size_t count, loff_t *off) {
WARN(true, "This message is generated from 'WARN'.\n");
WARN_ONCE(true, "This message is generated from 'WARN_ONCE', and should"
" appear once.\n");
return count;
}
static struct file_operations printk_fops = {
.read = printk_read,
.write = printk_write,
};
static struct miscdevice printk_device = {
.minor = MISC_DYNAMIC_MINOR,
.name = "printk",
.fops = &printk_fops,
};
static int __init printk_init(void) {
int retval = 0;
retval = misc_register(&printk_device);
if (retval != 0)
pr_warn("Couldn't register device!\n");
// BUILD_BUG_ON_MSG(true, "this line should be commented.");
return retval;
}
static void __exit printk_exit(void) {
misc_deregister(&printk_device);
}
module_init(printk_init);
module_exit(printk_exit);
MODULE_LICENSE("GPL");
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