#include <linux/ptrace.h>
  #include <linux/sched.h>
  #include <linux/export.h>
  #include <asm/syscall.h>
  
  static int collect_syscall(struct task_struct *target, long *callno,
  			   unsigned long args[6], unsigned int maxargs,
  			   unsigned long *sp, unsigned long *pc)
  {
  	struct pt_regs *regs = task_pt_regs(target);
  	if (unlikely(!regs))
  		return -EAGAIN;
  
  	*sp = user_stack_pointer(regs);
  	*pc = instruction_pointer(regs);
  
  	*callno = syscall_get_nr(target, regs);
  	if (*callno != -1L && maxargs > 0)
  		syscall_get_arguments(target, regs, 0, maxargs, args);
  
  	return 0;
  }
  
  /**
   * task_current_syscall - Discover what a blocked task is doing.
   * @target:		thread to examine
   * @callno:		filled with system call number or -1
   * @args:		filled with @maxargs system call arguments
   * @maxargs:		number of elements in @args to fill
   * @sp:			filled with user stack pointer
   * @pc:			filled with user PC
   *
   * If @target is blocked in a system call, returns zero with *@callno
   * set to the the call's number and @args filled in with its arguments.
   * Registers not used for system call arguments may not be available and
   * it is not kosher to use &struct user_regset calls while the system
   * call is still in progress.  Note we may get this result if @target
   * has finished its system call but not yet returned to user mode, such
   * as when it's stopped for signal handling or syscall exit tracing.
   *
   * If @target is blocked in the kernel during a fault or exception,
   * returns zero with *@callno set to -1 and does not fill in @args.
   * If so, it's now safe to examine @target using &struct user_regset
   * get() calls as long as we're sure @target won't return to user mode.
   *
   * Returns -%EAGAIN if @target does not remain blocked.
   *
   * Returns -%EINVAL if @maxargs is too large (maximum is six).
   */
  int task_current_syscall(struct task_struct *target, long *callno,
  			 unsigned long args[6], unsigned int maxargs,
  			 unsigned long *sp, unsigned long *pc)
  {
  	long state;
  	unsigned long ncsw;
  
  	if (unlikely(maxargs > 6))
  		return -EINVAL;
  
  	if (target == current)
  		return collect_syscall(target, callno, args, maxargs, sp, pc);
  
  	state = target->state;
  	if (unlikely(!state))
  		return -EAGAIN;
  
  	ncsw = wait_task_inactive(target, state);
  	if (unlikely(!ncsw) ||
  	    unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
  	    unlikely(wait_task_inactive(target, state) != ncsw))
  		return -EAGAIN;
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(task_current_syscall);