For in-kernel tty users, we need to be able to create and destroy
'struct tty' that are not associated with a file. The creation side is
fine, but tty_release() needs to be split into the file handle portion
and the struct tty portion. Introduce a new function, tty_release_struct,
to handle just the destroying of a struct tty.

Signed-off-by: Rob Herring <robh@kernel.org>
---
 drivers/tty/tty_io.c | 42 ++++++++++++++++++++++++------------------
 include/linux/tty.h  |  1 +
 2 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 734a635e7363..5ebc090ec47f 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c

@@ -1744,6 +1744,29 @@ static int tty_release_checks(struct tty_struct *tty, int idx)
 	return 0;
 }
 
+void tty_release_struct(struct tty_struct *tty, int idx)
+{
+	/*
+	 * Ask the line discipline code to release its structures
+	 */
+	tty_ldisc_release(tty);
+
+	/* Wait for pending work before tty destruction commmences */
+	tty_flush_works(tty);
+
+	tty_debug_hangup(tty, "freeing structure\n");
+	/*
+	 * The release_tty function takes care of the details of clearing
+	 * the slots and preserving the termios structure. The tty_unlock_pair
+	 * should be safe as we keep a kref while the tty is locked (so the
+	 * unlock never unlocks a freed tty).
+	 */
+	mutex_lock(&tty_mutex);
+	release_tty(tty, idx);
+	mutex_unlock(&tty_mutex);
+}
+EXPORT_SYMBOL_GPL(tty_release_struct);