tty: move the non-file related parts of tty_release to new tty_release_struct

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: NRob Herring <robh@kernel.org>
Reviewed-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-By: NSebastian Reichel <sre@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_io.c

@@ -1744,6 +1744,37 @@ static int tty_release_checks(struct tty_struct *tty, int idx)
 	return 0;
 }
 
+/**
+ *	tty_release_struct	-	release a tty struct
+ *	@tty: tty device
+ *	@idx: index of the tty
+ *
+ *	Performs the final steps to release and free a tty device. It is
+ *	roughly the reverse of tty_init_dev.
+ */
+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);
+
 /**
  *	tty_release		-	vfs callback for close
  *	@inode: inode of tty
@@ -1898,25 +1929,8 @@ int tty_release(struct inode *inode, struct file *filp)
 		return 0;
 
 	tty_debug_hangup(tty, "final close\n");
-	/*
-	 * 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);
 
+	tty_release_struct(tty, idx);
 	return 0;
 }
 

include/linux/tty.h

@@ -528,6 +528,7 @@ extern int tty_alloc_file(struct file *file);
 extern void tty_add_file(struct tty_struct *tty, struct file *file);
 extern void tty_free_file(struct file *file);
 extern struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx);
+extern void tty_release_struct(struct tty_struct *tty, int idx);
 extern int tty_release(struct inode *inode, struct file *filp);
 extern void tty_init_termios(struct tty_struct *tty);
 extern int tty_standard_install(struct tty_driver *driver,