Add procfs and kernel topic page

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+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
+
+
+
+