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>

1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/net/ppp_async.c b/drivers/net/ppp_async.c
index f023d5b67e6e..1c4b7e37912c 100644
--- a/drivers/net/ppp_async.c
+++ b/drivers/net/ppp_async.c
@@ -158,6 +158,9 @@ ppp_asynctty_open(struct tty_struct *tty)
         struct asyncppp *ap;
         int err;
 
+        if (tty->ops->write == NULL)
+                return -EOPNOTSUPP;
+
         err = -ENOMEM;
         ap = kzalloc(sizeof(*ap), GFP_KERNEL);
         if (!ap)
@@ -359,8 +362,8 @@ ppp_asynctty_receive(struct tty_struct *tty, const unsigned char *buf,
                 tasklet_schedule(&ap->tsk);
         ap_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
@@ -676,7 +679,7 @@ ppp_async_push(struct asyncppp *ap)
                 if (!tty_stuffed && ap->optr < ap->olim) {
                         avail = ap->olim - ap->optr;
                         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
-                        sent = tty->driver->write(tty, ap->optr, avail);
+                        sent = tty->ops->write(tty, ap->optr, avail);
                         if (sent < 0)
                                 goto flush;     /* error, e.g. loss of CD */
                         ap->optr += sent;