Kali Linux (VBox) : "linux/init.h: no such file or directory" (Makefile is present)

Question

I am trying to do the following - Writing a kernel module that lists all current tasks in a Linux system beginning from the init task. Output the task name (known as executable name), state and process id of each task in a tree structure.

The Error I am getting is this : (when I run the C program named "p1.c") Compile error: linux/init.h: No such file or directory

The p1.c program is:

#include <init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched/task.h>

/*OS Project_Final*/

void dfs(struct task_struct *task, int indent)
{
    struct task_struct *task_next;
    struct list_head *list;
    
    indent += 5;
    list_for_each(list, &task->children);
    task_next = list_entry(list, struct task_struct, sibling);
    
    printk("%*s pid: %d pname: %s state :%d#n", indent, "", task_next->pid, task_next->comm, task_next->state);
    
    dfs(task_next, indent);
}


int dfs_init(void)
{
    printk("Loading module\n");
    printk("pid: %d pname: %s state: %d\n", init_task.pid, init_task.comm, init_task.state);
    dfs(&init-task, 0);
    
    printk("Module Loaded\n");
    return 0;
}


void dfs_exit(void)
{
    printk("Module removed\n");
}

module_init(dfs_init);
module_exit(dfs_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Simple Module");
MODULE_AUTHOR("XXXXXX");

I am getting the error when I ran the command: gcc -c p1.c

and the MakeFile is placed in the directory named header (The header is located in the same directory as the p1.c C file)

Makefile is as below:

obj-m += p1.o

all:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules   
clean:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

How to resolve this error?

I tried running the following commands -

sudo apt install linux-headers-generic & sudo apt install make. But despite this, I am getting the same error.