Cannot include unistd.h in Linux kernel module

Question

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 directory If 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?

Answer 1

You're working with kernel code. There's no C standard library in the kernel! You cannot include standard headers like unistd.h or use most C standard library functions like getppid() .

If you want to get the PID of the current parent process from a kernel module you can get it from current->real_parent .

ppid = rcu_dereference(current->real_parent)->pid;