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Linux Kernel /proc Interface

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

By thelinuxchannel #ioctl interface, #Kernel Data Structures, #kernel module programming, #kernel programming, #kernel to user space, #Linux device drivers, #proc filesystem, #sysfs filesystem, #systems software developer
Linux Kernel /proc Interface - create and read /proc fileLinux Kernel /proc Interface - create and read /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
 * Author: Kiran Kankipati
 * Updated: 22-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;

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;
	//int abc=100;
	//strcpy(buf, "abc: %d\n", abc);
	//sprintf(buf, "abc: %d\n", abc);
	memset(buf,0xaa,10);
	//return strlen(buf);
	return 10;
}

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

static int hello_init(void)
{
 	tlc_proc_a = proc_create( "tlc_proc_a", 0444, 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

IMPORTANT NOTE: None of these sample code published in the below episodes will no longer work in a modern recent kernel versions (i.e especially those which are released after 2019 or so). So here are my video episodes performing a live kernel module code porting of episode – 191 Linux Kernel /proc Interface – create and read /proc file. If you want to make the other episode sample demo code to work then you just follow and repeat these steps.

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

/* proc_example.c
 * Author: Kiran Kankipati
 * Updated: 03-Mar-2021
 * Release notes: this is my updated (ported) code of my earlier (22-feb-2017) Kernel module code
   which creates a sample /proc file and allows us to read its contents from the user-space.
 */
#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;

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;
	//int abc=100;
	//strcpy(buf, "abc: %d\n", abc);
	//sprintf(buf, "abc: %d\n", abc);
	memset(buf,0xaa,10);
	//return strlen(buf);
	return 10;
}

static struct proc_ops tlc_proc_a_fops = { .proc_read=tlc_proc_a_read, };

static int hello_init(void)
{
 	tlc_proc_a = proc_create( "tlc_proc_a", 0444, 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);

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

/* proc_example.c
 * Author: Kiran Kankipati
 * Updated: 03-Mar-2021
 * Release notes: this is my updated (ported) code of my earlier (22-feb-2017) Kernel module code
   which creates a sample /proc file and allows us to read its contents from the user-space.
 *  
 * Updated: 28-Apr-2022
 * Release notes: added the module license and metadata.
 * compatible with: 5.13.0-41-generic (Ubuntu 21.10) - as well tested with: 5.15.0-27-generic (Ubuntu 22.04 LTS)
 */
#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;

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;
	//int abc=100;
	//strcpy(buf, "abc: %d\n", abc);
	//sprintf(buf, "abc: %d\n", abc);
	memset(buf,0xaa,10);
	//return strlen(buf);
	return 10;
}

static struct proc_ops tlc_proc_a_fops = { .proc_read=tlc_proc_a_read, };

static int hello_init(void)
{  
 	tlc_proc_a = proc_create( "tlc_proc_a", 0444, 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);

MODULE_DESCRIPTION("Sample /proc read access file");
MODULE_AUTHOR("Copyright(c) 2022 - Kiran Kankipati");
MODULE_LICENSE("GPL v2");
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