n_tty: Only flush echo output if actually output

Don't have the driver flush received echoes if no echoes were
actually output.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 10 insertions, 8 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 20983afb6086..59f3f10f37f3 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -646,14 +646,14 @@ break_out:
  *      Locking: callers must hold output_lock
  */
 
-static void __process_echoes(struct tty_struct *tty)
+static size_t __process_echoes(struct tty_struct *tty)
 {
         struct n_tty_data *ldata = tty->disc_data;
-        int     space, nr;
+        int     space, old_space;
         size_t tail;
         unsigned char c;
 
-        space = tty_write_room(tty);
+        old_space = space = tty_write_room(tty);
 
         tail = ldata->echo_tail;
         nr = ldata->echo_commit - ldata->echo_tail;
@@ -785,12 +785,13 @@ static void __process_echoes(struct tty_struct *tty)
         }
 
         ldata->echo_tail = tail;
+        return old_space - space;
 }
 
 static void commit_echoes(struct tty_struct *tty)
 {
         struct n_tty_data *ldata = tty->disc_data;
-        size_t nr, old;
+        size_t nr, old, echoed;
         size_t head;
 
         head = ldata->echo_head;
@@ -805,25 +806,26 @@ static void commit_echoes(struct tty_struct *tty)
 
         mutex_lock(&ldata->output_lock);
         ldata->echo_commit = head;
-        __process_echoes(tty);
+        echoed = __process_echoes(tty);
         mutex_unlock(&ldata->output_lock);
 
-        if (tty->ops->flush_chars)
+        if (echoed && tty->ops->flush_chars)
                 tty->ops->flush_chars(tty);
 }
 
 static void process_echoes(struct tty_struct *tty)
 {
         struct n_tty_data *ldata = tty->disc_data;
+        size_t echoed;
 
         if (!L_ECHO(tty) || ldata->echo_commit == ldata->echo_tail)
                 return;
 
         mutex_lock(&ldata->output_lock);
-        __process_echoes(tty);
+        echoed = __process_echoes(tty);
         mutex_unlock(&ldata->output_lock);
 
-        if (tty->ops->flush_chars)
+        if (echoed && tty->ops->flush_chars)
                 tty->ops->flush_chars(tty);
 }