Merge branch 'tty-splice' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux into tty-next

Fixes both the "splice/sendfile to a tty" and "splice/sendfile from a
tty" regression from 5.10.

* 'tty-splice' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux:
tty: teach the n_tty ICANON case about the new "cookie continuations" too
tty: teach n_tty line discipline about the new "cookie continuations"
tty: clean up legacy leftovers from n_tty line discipline
tty: implement read_iter
tty: convert tty_ldisc_ops 'read()' function to take a kernel pointer
tty: implement write_iter

drivers/bluetooth/hci_ldisc.c

···
  * We don't provide read/write/poll interface for user space.
  */
 static ssize_t hci_uart_tty_read(struct tty_struct *tty, struct file *file,
-				 unsigned char __user *buf, size_t nr)
+				 unsigned char *buf, size_t nr,
+				 void **cookie, unsigned long offset)
 {
 	return 0;
 }
···
 	return 0;
 }
 
+static struct tty_ldisc_ops hci_uart_ldisc = {
+	.owner		= THIS_MODULE,
+	.magic		= TTY_LDISC_MAGIC,
+	.name		= "n_hci",
+	.open		= hci_uart_tty_open,
+	.close		= hci_uart_tty_close,
+	.read		= hci_uart_tty_read,
+	.write		= hci_uart_tty_write,
+	.ioctl		= hci_uart_tty_ioctl,
+	.compat_ioctl	= hci_uart_tty_ioctl,
+	.poll		= hci_uart_tty_poll,
+	.receive_buf	= hci_uart_tty_receive,
+	.write_wakeup	= hci_uart_tty_wakeup,
+};
+
 static int __init hci_uart_init(void)
 {
-	static struct tty_ldisc_ops hci_uart_ldisc;
 	int err;
 
 	BT_INFO("HCI UART driver ver %s", VERSION);
 
 	/* Register the tty discipline */
-
-	memset(&hci_uart_ldisc, 0, sizeof(hci_uart_ldisc));
-	hci_uart_ldisc.magic		= TTY_LDISC_MAGIC;
-	hci_uart_ldisc.name		= "n_hci";
-	hci_uart_ldisc.open		= hci_uart_tty_open;
-	hci_uart_ldisc.close		= hci_uart_tty_close;
-	hci_uart_ldisc.read		= hci_uart_tty_read;
-	hci_uart_ldisc.write		= hci_uart_tty_write;
-	hci_uart_ldisc.ioctl		= hci_uart_tty_ioctl;
-	hci_uart_ldisc.compat_ioctl	= hci_uart_tty_ioctl;
-	hci_uart_ldisc.poll		= hci_uart_tty_poll;
-	hci_uart_ldisc.receive_buf	= hci_uart_tty_receive;
-	hci_uart_ldisc.write_wakeup	= hci_uart_tty_wakeup;
-	hci_uart_ldisc.owner		= THIS_MODULE;
-
 	err = tty_register_ldisc(N_HCI, &hci_uart_ldisc);
 	if (err) {
 		BT_ERR("HCI line discipline registration failed. (%d)", err);

drivers/input/serio/serport.c

···
  * returning 0 characters.
  */
 
-static ssize_t serport_ldisc_read(struct tty_struct * tty, struct file * file, unsigned char __user * buf, size_t nr)
+static ssize_t serport_ldisc_read(struct tty_struct * tty, struct file * file,
+				  unsigned char *kbuf, size_t nr,
+				  void **cookie, unsigned long offset)
 {
 	struct serport *serport = (struct serport*) tty->disc_data;
 	struct serio *serio;

drivers/net/ppp/ppp_async.c

···
  */
 static ssize_t
 ppp_asynctty_read(struct tty_struct *tty, struct file *file,
-		  unsigned char __user *buf, size_t count)
+		  unsigned char *buf, size_t count,
+		  void **cookie, unsigned long offset)
 {
 	return -EAGAIN;
 }

drivers/net/ppp/ppp_synctty.c

···
  */
 static ssize_t
 ppp_sync_read(struct tty_struct *tty, struct file *file,
-	       unsigned char __user *buf, size_t count)
+	      unsigned char *buf, size_t count,
+	      void **cookie, unsigned long offset)
 {
 	return -EAGAIN;
 }

drivers/tty/n_gsm.c

···
  */
 
 static ssize_t gsmld_read(struct tty_struct *tty, struct file *file,
-			 unsigned char __user *buf, size_t nr)
+			  unsigned char *buf, size_t nr,
+			  void **cookie, unsigned long offset)
 {
 	return -EOPNOTSUPP;
 }

drivers/tty/n_hdlc.c

···
  * Returns the number of bytes returned or error code.
  */
 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
-			   __u8 __user *buf, size_t nr)
+			   __u8 *kbuf, size_t nr,
+			   void **cookie, unsigned long offset)
 {
 	struct n_hdlc *n_hdlc = tty->disc_data;
 	int ret = 0;
 	struct n_hdlc_buf *rbuf;
 	DECLARE_WAITQUEUE(wait, current);
+
+	/* Is this a repeated call for an rbuf we already found earlier? */
+	rbuf = *cookie;
+	if (rbuf)
+		goto have_rbuf;
 
 	add_wait_queue(&tty->read_wait, &wait);
 
···
 		set_current_state(TASK_INTERRUPTIBLE);
 
 		rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
-		if (rbuf) {
-			if (rbuf->count > nr) {
-				/* too large for caller's buffer */
-				ret = -EOVERFLOW;
-			} else {
-				__set_current_state(TASK_RUNNING);
-				if (copy_to_user(buf, rbuf->buf, rbuf->count))
-					ret = -EFAULT;
-				else
-					ret = rbuf->count;
-			}
-
-			if (n_hdlc->rx_free_buf_list.count >
-			    DEFAULT_RX_BUF_COUNT)
-				kfree(rbuf);
-			else
-				n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
+		if (rbuf)
 			break;
-		}
 
 		/* no data */
 		if (tty_io_nonblock(tty, file)) {
···
 
 	remove_wait_queue(&tty->read_wait, &wait);
 	__set_current_state(TASK_RUNNING);
+
+	if (!rbuf)
+		return ret;
+	*cookie = rbuf;
+
+have_rbuf:
+	/* Have we used it up entirely? */
+	if (offset >= rbuf->count)
+		goto done_with_rbuf;
+
+	/* More data to go, but can't copy any more? EOVERFLOW */
+	ret = -EOVERFLOW;
+	if (!nr)
+		goto done_with_rbuf;
+
+	/* Copy as much data as possible */
+	ret = rbuf->count - offset;
+	if (ret > nr)
+		ret = nr;
+	memcpy(kbuf, rbuf->buf+offset, ret);
+	offset += ret;
+
+	/* If we still have data left, we leave the rbuf in the cookie */
+	if (offset < rbuf->count)
+		return ret;
+
+done_with_rbuf:
+	*cookie = NULL;
+
+	if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
+		kfree(rbuf);
+	else
+		n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
 
 	return ret;
 

drivers/tty/n_null.c

···
 }
 
 static ssize_t n_null_read(struct tty_struct *tty, struct file *file,
-			   unsigned char __user * buf, size_t nr)
+			   unsigned char *buf, size_t nr,
+			   void **cookie, unsigned long offset)
 {
 	return -EOPNOTSUPP;
 }

drivers/tty/n_r3964.c

···
 static int r3964_open(struct tty_struct *tty);
 static void r3964_close(struct tty_struct *tty);
 static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
-		unsigned char __user * buf, size_t nr);
+		void *cookie, unsigned char *buf, size_t nr);
 static ssize_t r3964_write(struct tty_struct *tty, struct file *file,
 		const unsigned char *buf, size_t nr);
 static int r3964_ioctl(struct tty_struct *tty, struct file *file,
···
 }
 
 static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
-			  unsigned char __user * buf, size_t nr)
+			  unsigned char *kbuf, size_t nr,
+			  void **cookie, unsigned long offset)
 {
 	struct r3964_info *pInfo = tty->disc_data;
 	struct r3964_client_info *pClient;
···
 		kfree(pMsg);
 		TRACE_M("r3964_read - msg kfree %p", pMsg);
 
-		if (copy_to_user(buf, &theMsg, ret)) {
-			ret = -EFAULT;
-			goto unlock;
-		}
+		memcpy(kbuf, &theMsg, ret);
 
 		TRACE_PS("read - return %d", ret);
 		goto unlock;

drivers/tty/n_tracerouter.c

···
  *	 -EINVAL
  */
 static ssize_t n_tracerouter_read(struct tty_struct *tty, struct file *file,
-				  unsigned char __user *buf, size_t nr) {
+				  unsigned char *buf, size_t nr,
+				  void **cookie, unsigned long offset)
+{
 	return -EINVAL;
 }
 

drivers/tty/n_tracesink.c

···
  *	 -EINVAL
  */
 static ssize_t n_tracesink_read(struct tty_struct *tty, struct file *file,
-				unsigned char __user *buf, size_t nr) {
+				unsigned char *buf, size_t nr,
+				void **cookie, unsigned long offset)
+{
 	return -EINVAL;
 }
 

drivers/tty/n_tty.c

···
 		memset(buffer, 0x00, size);
 }
 
-static int tty_copy_to_user(struct tty_struct *tty, void __user *to,
-			    size_t tail, size_t n)
+static void tty_copy(struct tty_struct *tty, void *to, size_t tail, size_t n)
 {
 	struct n_tty_data *ldata = tty->disc_data;
 	size_t size = N_TTY_BUF_SIZE - tail;
 	void *from = read_buf_addr(ldata, tail);
-	int uncopied;
 
 	if (n > size) {
 		tty_audit_add_data(tty, from, size);
-		uncopied = copy_to_user(to, from, size);
-		zero_buffer(tty, from, size - uncopied);
-		if (uncopied)
-			return uncopied;
+		memcpy(to, from, size);
+		zero_buffer(tty, from, size);
 		to += size;
 		n -= size;
 		from = ldata->read_buf;
 	}
 
 	tty_audit_add_data(tty, from, n);
-	uncopied = copy_to_user(to, from, n);
-	zero_buffer(tty, from, n - uncopied);
-	return uncopied;
+	memcpy(to, from, n);
+	zero_buffer(tty, from, n);
 }
 
 /**
···
 /**
  *	copy_from_read_buf	-	copy read data directly
  *	@tty: terminal device
- *	@b: user data
+ *	@kbp: data
  *	@nr: size of data
  *
  *	Helper function to speed up n_tty_read.  It is only called when
- *	ICANON is off; it copies characters straight from the tty queue to
- *	user space directly.  It can be profitably called twice; once to
- *	drain the space from the tail pointer to the (physical) end of the
- *	buffer, and once to drain the space from the (physical) beginning of
- *	the buffer to head pointer.
+ *	ICANON is off; it copies characters straight from the tty queue.
  *
  *	Called under the ldata->atomic_read_lock sem
+ *
+ *	Returns true if it successfully copied data, but there is still
+ *	more data to be had.
  *
  *	n_tty_read()/consumer path:
  *		caller holds non-exclusive termios_rwsem
  *		read_tail published
  */
 
-static int copy_from_read_buf(struct tty_struct *tty,
-				      unsigned char __user **b,
+static bool copy_from_read_buf(struct tty_struct *tty,
+				      unsigned char **kbp,
 				      size_t *nr)
 
 {
 	struct n_tty_data *ldata = tty->disc_data;
-	int retval;
 	size_t n;
 	bool is_eof;
 	size_t head = smp_load_acquire(&ldata->commit_head);
 	size_t tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
 
-	retval = 0;
 	n = min(head - ldata->read_tail, N_TTY_BUF_SIZE - tail);
 	n = min(*nr, n);
 	if (n) {
 		unsigned char *from = read_buf_addr(ldata, tail);
-		retval = copy_to_user(*b, from, n);
-		n -= retval;
+		memcpy(*kbp, from, n);
 		is_eof = n == 1 && *from == EOF_CHAR(tty);
 		tty_audit_add_data(tty, from, n);
 		zero_buffer(tty, from, n);
···
 		/* Turn single EOF into zero-length read */
 		if (L_EXTPROC(tty) && ldata->icanon && is_eof &&
 		    (head == ldata->read_tail))
-			n = 0;
-		*b += n;
+			return false;
+		*kbp += n;
 		*nr -= n;
+
+		/* If we have more to copy, let the caller know */
+		return head != ldata->read_tail;
 	}
-	return retval;
+	return false;
 }
 
 /**
  *	canon_copy_from_read_buf	-	copy read data in canonical mode
  *	@tty: terminal device
- *	@b: user data
+ *	@kbp: data
  *	@nr: size of data
  *
  *	Helper function for n_tty_read.  It is only called when ICANON is on;
  *	it copies one line of input up to and including the line-delimiting
- *	character into the user-space buffer.
+ *	character into the result buffer.
  *
  *	NB: When termios is changed from non-canonical to canonical mode and
  *	the read buffer contains data, n_tty_set_termios() simulates an EOF
···
  *		read_tail published
  */
 
-static int canon_copy_from_read_buf(struct tty_struct *tty,
-				    unsigned char __user **b,
-				    size_t *nr)
+static bool canon_copy_from_read_buf(struct tty_struct *tty,
+				     unsigned char **kbp,
+				     size_t *nr)
 {
 	struct n_tty_data *ldata = tty->disc_data;
 	size_t n, size, more, c;
 	size_t eol;
-	size_t tail;
-	int ret, found = 0;
+	size_t tail, canon_head;
+	int found = 0;
 
 	/* N.B. avoid overrun if nr == 0 */
 	if (!*nr)
-		return 0;
+		return false;
 
-	n = min(*nr + 1, smp_load_acquire(&ldata->canon_head) - ldata->read_tail);
+	canon_head = smp_load_acquire(&ldata->canon_head);
+	n = min(*nr + 1, canon_head - ldata->read_tail);
 
 	tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
 	size = min_t(size_t, tail + n, N_TTY_BUF_SIZE);
···
 	n_tty_trace("%s: eol:%zu found:%d n:%zu c:%zu tail:%zu more:%zu\n",
 		    __func__, eol, found, n, c, tail, more);
 
-	ret = tty_copy_to_user(tty, *b, tail, n);
-	if (ret)
-		return -EFAULT;
-	*b += n;
+	tty_copy(tty, *kbp, tail, n);
+	*kbp += n;
 	*nr -= n;
 
 	if (found)
···
 		else
 			ldata->push = 0;
 		tty_audit_push();
+		return false;
 	}
-	return 0;
+
+	/* No EOL found - do a continuation retry if there is more data */
+	return ldata->read_tail != canon_head;
 }
 
 extern ssize_t redirected_tty_write(struct file *, const char __user *,
···
  */
 
 static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
-			 unsigned char __user *buf, size_t nr)
+			  unsigned char *kbuf, size_t nr,
+			  void **cookie, unsigned long offset)
 {
 	struct n_tty_data *ldata = tty->disc_data;
-	unsigned char __user *b = buf;
+	unsigned char *kb = kbuf;
 	DEFINE_WAIT_FUNC(wait, woken_wake_function);
 	int c;
 	int minimum, time;
···
 	long timeout;
 	int packet;
 	size_t tail;
+
+	/*
+	 * Is this a continuation of a read started earler?
+	 *
+	 * If so, we still hold the atomic_read_lock and the
+	 * termios_rwsem, and can just continue to copy data.
+	 */
+	if (*cookie) {
+		if (ldata->icanon && !L_EXTPROC(tty)) {
+			if (canon_copy_from_read_buf(tty, &kb, &nr))
+				return kb - kbuf;
+		} else {
+			if (copy_from_read_buf(tty, &kb, &nr))
+				return kb - kbuf;
+		}
+
+		/* No more data - release locks and stop retries */
+		n_tty_kick_worker(tty);
+		n_tty_check_unthrottle(tty);
+		up_read(&tty->termios_rwsem);
+		mutex_unlock(&ldata->atomic_read_lock);
+		*cookie = NULL;
+		return kb - kbuf;
+	}
 
 	c = job_control(tty, file);
 	if (c < 0)
···
 		/* First test for status change. */
 		if (packet && tty->link->ctrl_status) {
 			unsigned char cs;
-			if (b != buf)
+			if (kb != kbuf)
 				break;
 			spin_lock_irq(&tty->link->ctrl_lock);
 			cs = tty->link->ctrl_status;
 			tty->link->ctrl_status = 0;
 			spin_unlock_irq(&tty->link->ctrl_lock);
-			if (put_user(cs, b)) {
-				retval = -EFAULT;
-				break;
-			}
-			b++;
+			*kb++ = cs;
 			nr--;
 			break;
 		}
···
 		}
 
 		if (ldata->icanon && !L_EXTPROC(tty)) {
-			retval = canon_copy_from_read_buf(tty, &b, &nr);
-			if (retval)
-				break;
+			if (canon_copy_from_read_buf(tty, &kb, &nr))
+				goto more_to_be_read;
 		} else {
-			int uncopied;
-
 			/* Deal with packet mode. */
-			if (packet && b == buf) {
-				if (put_user(TIOCPKT_DATA, b)) {
-					retval = -EFAULT;
-					break;
-				}
-				b++;
+			if (packet && kb == kbuf) {
+				*kb++ = TIOCPKT_DATA;
 				nr--;
 			}
 
-			uncopied = copy_from_read_buf(tty, &b, &nr);
-			uncopied += copy_from_read_buf(tty, &b, &nr);
-			if (uncopied) {
-				retval = -EFAULT;
-				break;
+			/*
+			 * Copy data, and if there is more to be had
+			 * and we have nothing more to wait for, then
+			 * let's mark us for retries.
+			 *
+			 * NOTE! We return here with both the termios_sem
+			 * and atomic_read_lock still held, the retries
+			 * will release them when done.
+			 */
+			if (copy_from_read_buf(tty, &kb, &nr) && kb - kbuf >= minimum) {
+more_to_be_read:
+				remove_wait_queue(&tty->read_wait, &wait);
+				*cookie = cookie;
+				return kb - kbuf;
 			}
 		}
 
 		n_tty_check_unthrottle(tty);
 
-		if (b - buf >= minimum)
+		if (kb - kbuf >= minimum)
 			break;
 		if (time)
 			timeout = time;
···
 	remove_wait_queue(&tty->read_wait, &wait);
 	mutex_unlock(&ldata->atomic_read_lock);
 
-	if (b - buf)
-		retval = b - buf;
+	if (kb - kbuf)
+		retval = kb - kbuf;
 
 	return retval;
 }

drivers/tty/tty_io.c

···
 /* Mutex to protect creating and releasing a tty */
 DEFINE_MUTEX(tty_mutex);
 
-static ssize_t tty_read(struct file *, char __user *, size_t, loff_t *);
-static ssize_t tty_write(struct file *, const char __user *, size_t, loff_t *);
-ssize_t redirected_tty_write(struct file *, const char __user *,
-							size_t, loff_t *);
+static ssize_t tty_read(struct kiocb *, struct iov_iter *);
+static ssize_t tty_write(struct kiocb *, struct iov_iter *);
+ssize_t redirected_tty_write(struct kiocb *, struct iov_iter *);
 static __poll_t tty_poll(struct file *, poll_table *);
 static int tty_open(struct inode *, struct file *);
 long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
···
 
 static const struct file_operations tty_fops = {
 	.llseek		= no_llseek,
-	.read		= tty_read,
-	.write		= tty_write,
+	.read_iter	= tty_read,
+	.write_iter	= tty_write,
+	.splice_read	= generic_file_splice_read,
+	.splice_write	= iter_file_splice_write,
 	.poll		= tty_poll,
 	.unlocked_ioctl	= tty_ioctl,
 	.compat_ioctl	= tty_compat_ioctl,
···
 
 static const struct file_operations console_fops = {
 	.llseek		= no_llseek,
-	.read		= tty_read,
-	.write		= redirected_tty_write,
+	.read_iter	= tty_read,
+	.write_iter	= redirected_tty_write,
+	.splice_read	= generic_file_splice_read,
+	.splice_write	= iter_file_splice_write,
 	.poll		= tty_poll,
 	.unlocked_ioctl	= tty_ioctl,
 	.compat_ioctl	= tty_compat_ioctl,
···
 	/* This breaks for file handles being sent over AF_UNIX sockets ? */
 	list_for_each_entry(priv, &tty->tty_files, list) {
 		filp = priv->file;
-		if (filp->f_op->write == redirected_tty_write)
+		if (filp->f_op->write_iter == redirected_tty_write)
 			cons_filp = filp;
-		if (filp->f_op->write != tty_write)
+		if (filp->f_op->write_iter != tty_write)
 			continue;
 		closecount++;
 		__tty_fasync(-1, filp, 0);	/* can't block */
···
 		time->tv_sec = sec;
 }
 
+/*
+ * Iterate on the ldisc ->read() function until we've gotten all
+ * the data the ldisc has for us.
+ *
+ * The "cookie" is something that the ldisc read function can fill
+ * in to let us know that there is more data to be had.
+ *
+ * We promise to continue to call the ldisc until it stops returning
+ * data or clears the cookie. The cookie may be something that the
+ * ldisc maintains state for and needs to free.
+ */
+static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty,
+		struct file *file, struct iov_iter *to)
+{
+	int retval = 0;
+	void *cookie = NULL;
+	unsigned long offset = 0;
+	char kernel_buf[64];
+	size_t count = iov_iter_count(to);
+
+	do {
+		int size, copied;
+
+		size = count > sizeof(kernel_buf) ? sizeof(kernel_buf) : count;
+		size = ld->ops->read(tty, file, kernel_buf, size, &cookie, offset);
+		if (!size)
+			break;
+
+		/*
+		 * A ldisc read error return will override any previously copied
+		 * data (eg -EOVERFLOW from HDLC)
+		 */
+		if (size < 0) {
+			memzero_explicit(kernel_buf, sizeof(kernel_buf));
+			return size;
+		}
+
+		copied = copy_to_iter(kernel_buf, size, to);
+		offset += copied;
+		count -= copied;
+
+		/*
+		 * If the user copy failed, we still need to do another ->read()
+		 * call if we had a cookie to let the ldisc clear up.
+		 *
+		 * But make sure size is zeroed.
+		 */
+		if (unlikely(copied != size)) {
+			count = 0;
+			retval = -EFAULT;
+		}
+	} while (cookie);
+
+	/* We always clear tty buffer in case they contained passwords */
+	memzero_explicit(kernel_buf, sizeof(kernel_buf));
+	return offset ? offset : retval;
+}
+
+
 /**
  *	tty_read	-	read method for tty device files
  *	@file: pointer to tty file
···
  *	read calls may be outstanding in parallel.
  */
 
-static ssize_t tty_read(struct file *file, char __user *buf, size_t count,
-			loff_t *ppos)
+static ssize_t tty_read(struct kiocb *iocb, struct iov_iter *to)
 {
 	int i;
+	struct file *file = iocb->ki_filp;
 	struct inode *inode = file_inode(file);
 	struct tty_struct *tty = file_tty(file);
 	struct tty_ldisc *ld;
···
 	/* We want to wait for the line discipline to sort out in this
 	   situation */
 	ld = tty_ldisc_ref_wait(tty);
-	if (!ld)
-		return hung_up_tty_read(file, buf, count, ppos);
-	if (ld->ops->read)
-		i = ld->ops->read(tty, file, buf, count);
-	else
-		i = -EIO;
+	i = -EIO;
+	if (ld && ld->ops->read)
+		i = iterate_tty_read(ld, tty, file, to);
 	tty_ldisc_deref(ld);
 
 	if (i > 0)
···
 	ssize_t (*write)(struct tty_struct *, struct file *, const unsigned char *, size_t),
 	struct tty_struct *tty,
 	struct file *file,
-	const char __user *buf,
-	size_t count)
+	struct iov_iter *from)
 {
+	size_t count = iov_iter_count(from);
 	ssize_t ret, written = 0;
 	unsigned int chunk;
 
···
 		size_t size = count;
 		if (size > chunk)
 			size = chunk;
+
 		ret = -EFAULT;
-		if (copy_from_user(tty->write_buf, buf, size))
+		if (copy_from_iter(tty->write_buf, size, from) != size)
 			break;
+
 		ret = write(tty, file, tty->write_buf, size);
 		if (ret <= 0)
 			break;
+
+		/* FIXME! Have Al check this! */
+		if (ret != size)
+			iov_iter_revert(from, size-ret);
+
 		written += ret;
-		buf += ret;
 		count -= ret;
 		if (!count)
 			break;
···
  *	write method will not be invoked in parallel for each device.
  */
 
-static ssize_t tty_write(struct file *file, const char __user *buf,
-						size_t count, loff_t *ppos)
+static ssize_t tty_write(struct kiocb *iocb, struct iov_iter *from)
 {
+	struct file *file = iocb->ki_filp;
 	struct tty_struct *tty = file_tty(file);
  	struct tty_ldisc *ld;
 	ssize_t ret;
···
 	if (tty->ops->write_room == NULL)
 		tty_err(tty, "missing write_room method\n");
 	ld = tty_ldisc_ref_wait(tty);
-	if (!ld)
-		return hung_up_tty_write(file, buf, count, ppos);
-	if (!ld->ops->write)
+	if (!ld || !ld->ops->write)
 		ret = -EIO;
 	else
-		ret = do_tty_write(ld->ops->write, tty, file, buf, count);
+		ret = do_tty_write(ld->ops->write, tty, file, from);
 	tty_ldisc_deref(ld);
 	return ret;
 }
 
-ssize_t redirected_tty_write(struct file *file, const char __user *buf,
-						size_t count, loff_t *ppos)
+ssize_t redirected_tty_write(struct kiocb *iocb, struct iov_iter *iter)
 {
 	struct file *p = NULL;
 
···
 
 	if (p) {
 		ssize_t res;
-		res = vfs_write(p, buf, count, &p->f_pos);
+		res = vfs_iocb_iter_write(p, iocb, iter);
 		fput(p);
 		return res;
 	}
-	return tty_write(file, buf, count, ppos);
+	return tty_write(iocb, iter);
 }
 
 /*
···
 {
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
-	if (file->f_op->write == redirected_tty_write) {
+	if (file->f_op->write_iter == redirected_tty_write) {
 		struct file *f;
 		spin_lock(&redirect_lock);
 		f = redirect;
···
 
 static int this_tty(const void *t, struct file *file, unsigned fd)
 {
-	if (likely(file->f_op->read != tty_read))
+	if (likely(file->f_op->read_iter != tty_read))
 		return 0;
 	return file_tty(file) != t ? 0 : fd + 1;
 }

include/linux/tty_ldisc.h

···
 	void	(*close)(struct tty_struct *);
 	void	(*flush_buffer)(struct tty_struct *tty);
 	ssize_t	(*read)(struct tty_struct *tty, struct file *file,
-			unsigned char __user *buf, size_t nr);
+			unsigned char *buf, size_t nr,
+			void **cookie, unsigned long offset);
 	ssize_t	(*write)(struct tty_struct *tty, struct file *file,
 			 const unsigned char *buf, size_t nr);
 	int	(*ioctl)(struct tty_struct *tty, struct file *file,

net/nfc/nci/uart.c

···
 
 /* We don't provide read/write/poll interface for user space. */
 static ssize_t nci_uart_tty_read(struct tty_struct *tty, struct file *file,
-				 unsigned char __user *buf, size_t nr)
+				 unsigned char *buf, size_t nr,
+				 void **cookie, unsigned long offset)
 {
 	return 0;
 }