tty: shutdown method

Right now there are various drivers that try to use tty->count to know when
they get the final close. Aristeau Rozanski showed while debugging the vt
sysfs race that this isn't entirely safe.

Instead of driver side tricks to work around this introduce a shutdown which
is called when the tty is being destructed. This also means that the shutdown
method is tied into the refcounting.

Use this to rework the console close/sysfs logic.

Remove lots of special case code from the tty core code. The pty code can now
have a shutdown() method that replaces the special case hackery in the tree
free up paths.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
index ac6e58e26b73..2322313a8589 100644
--- a/include/linux/tty_driver.h
+++ b/include/linux/tty_driver.h
@@ -21,6 +21,11 @@
  *
  *	Required method.
  *
+ * void (*shutdown)(struct tty_struct * tty);
+ *
+ * 	This routine is called when a particular tty device is closed for
+ *	the last time freeing up the resources.
+ *
  * int (*write)(struct tty_struct * tty,
  * 		 const unsigned char *buf, int count);
  *
@@ -200,6 +205,7 @@ struct tty_driver;
 struct tty_operations {
 	int  (*open)(struct tty_struct * tty, struct file * filp);
 	void (*close)(struct tty_struct * tty, struct file * filp);
+	void (*shutdown)(struct tty_struct *tty);
 	int  (*write)(struct tty_struct * tty,
 		      const unsigned char *buf, int count);
 	int  (*put_char)(struct tty_struct *tty, unsigned char ch);