title:Create procfs entry
keywords:kernel,linux,threads

# Create procfs entry

Lets extend hello world driver. 


__Makefile__
```Makefile
obj-m += procfs_entry.o

KDIR ?= /lib/modules/$(shell uname -r)/build

all:
	make -C $(KDIR) M=$(PWD) modules

clean:
	make -C $(KDIR) M=$(PWD) clean
```

__procfs_entry.c__
```c
#include <linux/module.h>  /* Needed by all modules */
#include <linux/kernel.h>

int procfs_entry_init( void )
{
	printk(KERN_DEBUG "Hello Procfs!\n");
	return 0;
}

void procfs_entry_exit( void )
{
	printk(KERN_DEBUG "Exit Procfs!\n");
}

module_init( procfs_entry_init );
module_exit( procfs_entry_exit );

MODULE_LICENSE("GPL");
```


Create proc directory with

```c
dir = proc_mkdir(DIR_NAME, PARENT_DIR);
```

under the directory create file that will contain data

```c
proc_create("file", MODE, PARENT_DIR, PROC_FOPS)
```

Lets create /proc/secret/file. And define basic read/write operations. That at this 
stage will do nothing.

```c
#include <linux/proc_fs.h>

static struct proc_dir_entry *procdir, *procfile;

static int secret_open(struct inode *inode, struct file *file) {
        return 0;
}

static int secret_release(struct inode *inode, struct file *file) {
        return 0;
}

static ssize_t secret_read(struct file *file, char __user *buffer, size_t length, loff_t *offset) {
        return 0;
}

static ssize_t secret_write(struct file *file, const char *buffer, size_t length, loff_t *offset) {
        return 0;
}

static struct proc_ops procfs_ops = {
        .proc_open = secret_open,
        .proc_read = secret_read,
        .proc_write = secret_write,
        .proc_release = secret_release
};


int procfs_entry_init( void ) {
...
procdir = proc_mkdir("secret", NULL);
if (procdir == NULL) {
	pr_err("Cant create secret directory\n");
	return -1;
}

procfile = proc_create("file", 0644, procdir, &procfs_ops);
if (procfile == NULL) {
	pr_err("Cant create file under the secret\n");
	return -1;
}
...
}

void procfs_entry_exit( void )
{
	...
	//remove entries after unloading module
	proc_remove(procdir);
	proc_remove(procfile);
	...
}
```

Next step add data to read from file entry




## List of procfs functions used

| Function name | Note |
|---|---|
| proc_mkdir | Create procfs directory |
| proc_create | Create procfs file |
| proc_remove | Remove procfs entry |

## Final result

__Makefile__
```Makefile
```

__procfs_entry.c__
```c
```

## Links

https://elixir.bootlin.com/linux/v6.1.21/source/include/linux/proc_fs.h