tty: The big operations rework

- Operations are now a shared const function block as with most other Linux
  objects

- Introduce wrappers for some optional functions to get consistent behaviour

- Wrap put_char which used to be patched by the tty layer

- Document which functions are needed/optional

- Make put_char report success/fail

- Cache the driver->ops pointer in the tty as tty->ops

- Remove various surplus lock calls we no longer need

- Remove proc_write method as noted by Alexey Dobriyan

- Introduce some missing sanity checks where certain driver/ldisc
  combinations would oops as they didn't check needed methods were present

[akpm@linux-foundation.org: fix fs/compat_ioctl.c build]
[akpm@linux-foundation.org: fix isicom]
[akpm@linux-foundation.org: fix arch/ia64/hp/sim/simserial.c build]
[akpm@linux-foundation.org: fix kgdb]
Signed-off-by: Alan Cox <alan@redhat.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/net/ppp_synctty.c

@@ -207,6 +207,9 @@ ppp_sync_open(struct tty_struct *tty)
 	struct syncppp *ap;
 	int err;
 
+	if (tty->ops->write == NULL)
+		return -EOPNOTSUPP;
+
 	ap = kzalloc(sizeof(*ap), GFP_KERNEL);
 	err = -ENOMEM;
 	if (!ap)
@@ -399,8 +402,8 @@ ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
 		tasklet_schedule(&ap->tsk);
 	sp_put(ap);
 	if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
-	    && tty->driver->unthrottle)
-		tty->driver->unthrottle(tty);
+	    && tty->ops->unthrottle)
+		tty->ops->unthrottle(tty);
 }
 
 static void
@@ -653,7 +656,7 @@ ppp_sync_push(struct syncppp *ap)
 			tty_stuffed = 0;
 		if (!tty_stuffed && ap->tpkt) {
 			set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
-			sent = tty->driver->write(tty, ap->tpkt->data, ap->tpkt->len);
+			sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len);
 			if (sent < 0)
 				goto flush;	/* error, e.g. loss of CD */
 			if (sent < ap->tpkt->len) {