Cannot include unistd.h in Linux kernel module

I need to traverse all current processes with DFS(Depth First Search) in linux with C. I need to get parent process name and parent process id of the process named gedit. I'm trying to use getppid function. Here is the code:

#include <linux/init.h>#include <linux/module.h>#include <linux/kernel.h>#include <linux/sched.h>// Not sure of these two include statements:#include <linux/types.h>#include <unistd.h>/* performs a depth-first traversal of the list of tasks in the system. */void traverse(struct task_struct *ptr) {    struct list_head *list;    struct task_struct *next_task;    pid_t ppid;    if ((thread_group_leader(ptr)) && (strcmp(ptr->comm,"gedit")==0)) {              ppid = getppid();              printk(KERN_INFO "PID:%d\n",ppid); }    list_for_each(list, &ptr->children) {        next_task = list_entry(list, struct task_struct, sibling);        traverse(next_task);    }}int simple_init(void){     printk(KERN_INFO "Loading Module\n");     printk(KERN_INFO "Gedit's parent process:\n");     traverse(&init_task);     return 0;}void simple_exit(void) {    printk(KERN_INFO "Removing Module\n");}module_init( simple_init );module_exit( simple_exit );

I get this error: unistd.h no such file or directoryIf I try to include linux/unistd.h, I get implicit decleration of getppid function error.

Traversal works, the only problem is libraries and getppid function. Can anyone help me with this?