Linux Kernel /proc Interface – create and write /proc file

/proc is one of the most popular kernel to user-space interface which you can leverage to add an interface to your Kernel code such as Kernel modules, Kernel Device Drivers, etc. Personally I prefer /proc interface than other alternatives such as /sysfs, ioctl() and so on for my personal Kernel modules/stack.

So here is my detailed multi-episode Youtube video series on /proc Interface.

Here is my sample source-code discussed in the video:

/* proc_example.c - write /proc file
 * Author: Kiran Kankipati
 * Updated: 23-feb-2017
 */
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/module.h> 
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/skbuff.h>  
#include <linux/udp.h>
#include <linux/ip.h>
#include <linux/in.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/inet.h>
#include <linux/inetdevice.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/if_arp.h>
#include <linux/icmp.h>
#include <linux/proc_fs.h>
#include <linux/netlink.h>
#include <linux/mroute.h>
#include <net/checksum.h>
#include <net/inet_ecn.h>
#include <net/xfrm.h>
#include <net/route.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/tcp.h>
#include <net/arp.h>
#include <net/udp.h>
#include <net/icmp.h>
#include <net/inetpeer.h>
#include <net/protocol.h>
#include <net/flow.h>
#include <asm/types.h>

struct proc_dir_entry *tlc_proc_a;

int abc=100;

#define PROCFS_MAX_SIZE 30
char proc_buf[PROCFS_MAX_SIZE];

static ssize_t tlc_proc_a_write(struct file *fp, const char *buf, size_t len, loff_t * off)
{	if(len > PROCFS_MAX_SIZE) { return -EFAULT; }
   if(copy_from_user(proc_buf, buf, len)) { return -EFAULT; }

	abc=simple_strtoul(proc_buf,NULL,10);
	return len;
}


static ssize_t tlc_proc_a_read(struct file *fp, char *buf, size_t len, loff_t * off)
{	static int finished=0; if(finished) {finished=0;return 0;} finished=1;
	
	sprintf(buf, "abc: %d\n", abc);
	return strlen(buf);
}

static struct file_operations tlc_proc_a_fops = { .owner=THIS_MODULE, .read=tlc_proc_a_read, .write=tlc_proc_a_write, };

static int hello_init(void)
{
 	tlc_proc_a = proc_create( "tlc_proc_a", 0666, NULL, &tlc_proc_a_fops); 
 	if(tlc_proc_a==NULL) {	printk(KERN_ALERT "Error: Could not initialize %s\n", "tlc_proc_a"); }
	
	return 0;
}

static void hello_exit(void) 
{  remove_proc_entry("tlc_proc_a", NULL);
}

module_init(hello_init);
module_exit(hello_exit);

Its makefile:

obj-m += proc_example.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules