fault-inject: make fail-nth read/write interface symmetric

- /proc/self/task/<current-tid>/fail-nth:

	Write to this file of integer N makes N-th call in the task fail.

	Read from this file returns a single char 'Y' or 'N'

	that says if the fault setup with a previous write to this file was

	injected or not, and disables the fault if it wasn't yet injected.

	Read from this file returns a integer value. A value of '0' indicates

	that the fault setup with a previous write to this file was injected.

	A positive integer N indicates that the fault wasn't yet injected.

	Note that this file enables all types of faults (slab, futex, etc).

	This setting takes precedence over all other generic debugfs settings

	like probability, interval, times, etc. But per-capability settings

		write(fail_nth, buf, strlen(buf));

		res = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds);

		err = errno;

		read(fail_nth, buf, 1);

		pread(fail_nth, buf, sizeof(buf), 0);

		if (res == 0) {

			close(fds[0]);

			close(fds[1]);

		}

		printf("%d-th fault %c: res=%d/%d\n", i, buf[0], res, err);

		if (buf[0] != 'Y')

		printf("%d-th fault %c: res=%d/%d\n", i, atoi(buf) ? 'N' : 'Y',

			res, err);

		if (atoi(buf))

			break;

	}

	return 0;

				  size_t count, loff_t *ppos)

{

	struct task_struct *task;

	int err;

	char numbuf[PROC_NUMBUF];

	ssize_t len;

	task = get_proc_task(file_inode(file));

	if (!task)

	put_task_struct(task);

	if (task != current)

		return -EPERM;

	if (count < 1)

		return -EINVAL;

	err = put_user((char)(current->fail_nth ? 'N' : 'Y'), buf);

	if (err)

		return err;

	current->fail_nth = 0;

	return 1;

	len = snprintf(numbuf, sizeof(numbuf), "%u\n", task->fail_nth);

	len = simple_read_from_buffer(buf, count, ppos, numbuf, len);

	return len;

}

static const struct file_operations proc_fail_nth_operations = {