Linux kernel module: Add entry in /proc and passing args while insmod

Goal 

Implement a kernel module that can passing parameter when insert module, and add an entry to /proc that can write/read data. In embedded linux often using similar facility to help debug.

Code:

	#include <linux/module.h>
	#include <linux/moduleparam.h>
	#include <linux/init.h>
	#include <linux/kernel.h>
	#include <linux/proc_fs.h>
	#include <linux/uaccess.h>
	#define BUFSIZE 100
	MODULE_LICENSE("GPL");
	MODULE_AUTHOR("Ray Tsai");
	static int mode=0;
	module_param(mode,int,0660);
	static char *entry="Default";
	module_param(entry,charp,0660);
	// Proc related structure
	static struct proc_dir_entry *ent;
	static int private_test_data = 123;
	// Write handler
	static ssize_t test_write(struct file *file, const char __user *ubuf,size_t count, loff_t *ppos)
	{
	char buf[BUFSIZE];
	int temp = 0;
	int num =0;
	pr_info( KERN_DEBUG "write handler\n");
	if(copy_from_user(buf, ubuf, count))
	{
	pr_info( KERN_DEBUG "Error copy from user \n");
	return -EFAULT;
	}
	num = sscanf(buf,"%d",&temp);
	private_test_data = temp;
	return count;
	}
	// Read handler
	static ssize_t test_read(struct file *file, char __user *ubuf,size_t count, loff_t *ppos)
	{
	char buf[BUFSIZE];
	int len=0;
	pr_info( KERN_DEBUG "read handler\n");
	if(*ppos > 0 || count < BUFSIZE)
	return 0;
	len += sprintf(buf,"private_test_data = %d\n",private_test_data);
	if(copy_to_user(ubuf,buf,len))
	return -EFAULT;
	*ppos = len;
	return len;
	}
	static struct file_operations myops =
	{
	.owner = THIS_MODULE,
	.read = test_read,
	.write = test_write,
	};
	static int __init test_module_init(void)
	{
	pr_info("Init Ray test module!\n");
	pr_info("Test module: %d!\n", mode);
	pr_info("Create %s \n", entry);
	ent = proc_create(entry,0660,NULL,&myops);
	return 0;
	}
	static void __exit test_module_exit(void)
	{
	proc_remove(ent);
	pr_info("Exit Ray test module!\n");
	}
	module_init(test_module_init);
	module_exit(test_module_exit);

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Makefile:

	obj-m := test_module.o
	KERNELDIR ?= /lib/modules/$(shell uname -r)/build
	all default: modules
	install: modules_install
	modules modules_install help clean:
	$(MAKE) -C $(KERNELDIR) M=$(shell pwd) $@

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Usage:

1. Insert module and make /proc/Ray entry

 #>sudo insmod test_module.ko entry="Ray" mode=1238

 

2. Write data 

#>echo 123 > /proc/Ray

3. Read data

 #>cat /proc/Ray

 

Reference:

1. Linux Device Drivers Development: Develop customized drivers for embedded Linux
2. LINUX KERNEL DEVELOPMENT – CREATING A PROC FILE AND INTERFACING WITH USER SPACE