AOS HW2 system call that collect info of caller process

dummysyscall.c

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <uapi/linux/errno.h>
#include <asm/uaccess.h>
#include <linux/string.h>
#include <linux/list.h>
#include <linux/sched.h>

#include "dummysyscall.h"

long sys_dummy(struct prinfo *info) {

  struct prinfo kinfo;
  struct task_struct *task = NULL;
  struct list_head *list = NULL;
  pid_t childpid = 0;
  pid_t pid_young = 32768;
  pid_t pid_old = 0;

  if (copy_from_user(&kinfo, info, sizeof(struct prinfo))) {
    return -EFAULT;
  }


  kinfo.state               = current->state;
  kinfo.nice                = task_nice(current);
  kinfo.pid                 = current->pid;
  kinfo.parent_pid          = current->parent->pid;

  // find child with largest pid
  printk("current pid %d\n", current->pid);
  list_for_each(list, &current->children) {
    task = list_entry(list, struct task_struct, sibling);
    printk("child pid %d\n", task->pid);
    if (task && task->pid > childpid) {
      childpid = task->pid;
    }
  }

  // find younger/older sibling
  printk("current pid %d\n", current->pid);
  list_for_each(list, &current->parent->children) {
    task = list_entry(list, struct task_struct, sibling);
    printk("sibling pid %d\n", task->pid);
    if (task->pid > current->pid && task->pid < pid_young) {
      pid_young = task->pid;
    }
    if (task->pid < current->pid && task->pid > pid_old) {
      pid_old = task->pid;
    }
  }

  kinfo.youngest_child_pid  = childpid;
  kinfo.younger_sibling_pid = pid_young;
  kinfo.older_sibling_pid   = pid_old;
  kinfo.start_time          = current->start_time;
  kinfo.user_time           = current->utime;
  kinfo.sys_time            = current->stime;
  kinfo.cutime              = current->signal->cutime;
  kinfo.cstime              = current->signal->cstime;
  kinfo.uid                 = current->cred->uid.val;
  strncat(kinfo.comm, current->comm, 16);

  if (copy_to_user(info, &kinfo, sizeof(struct prinfo))) {
    return -EFAULT;
  }

  return 0;
}