tty: Extract various bits of ldisc code

Before trying to tackle the ldisc bugs the code needs to be a good deal
more readable, so do the simple extractions of routines first.

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

3 files changed, 88 insertions, 36 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 6c817398232e..be49d0730bb9 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -2481,6 +2481,24 @@ static int tty_tiocmset(struct tty_struct *tty, struct file *file, unsigned int
         return tty->ops->tiocmset(tty, file, set, clear);
 }
 
+struct tty_struct *tty_pair_get_tty(struct tty_struct *tty)
+{
+        if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
+            tty->driver->subtype == PTY_TYPE_MASTER)
+                tty = tty->link;
+        return tty;
+}
+EXPORT_SYMBOL(tty_pair_get_tty);
+
+struct tty_struct *tty_pair_get_pty(struct tty_struct *tty)
+{
+        if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
+            tty->driver->subtype == PTY_TYPE_MASTER)
+            return tty;
+        return tty->link;
+}
+EXPORT_SYMBOL(tty_pair_get_pty);
+
 /*
  * Split this up, as gcc can choke on it otherwise..
  */
@@ -2496,11 +2514,7 @@ long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
         if (tty_paranoia_check(tty, inode, "tty_ioctl"))
                 return -EINVAL;
 
-        real_tty = tty;
-        if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
-            tty->driver->subtype == PTY_TYPE_MASTER)
-                real_tty = tty->link;
-
+        real_tty = tty_pair_get_tty(tty);
 
         /*
          * Factor out some common prep work
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index f78f5b0127a8..e3c6416aa86d 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -444,6 +444,50 @@ static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
 }
 
 /**
+ *      tty_ldisc_halt          -       shutdown the line discipline
+ *      @tty: tty device
+ *
+ *      Shut down the line discipline and work queue for this tty device.
+ *      The TTY_LDISC flag being cleared ensures no further references can
+ *      be obtained while the delayed work queue halt ensures that no more
+ *      data is fed to the ldisc.
+ *
+ *      In order to wait for any existing references to complete see 
+ *      tty_ldisc_wait_idle.
+ */
+
+static void tty_ldisc_halt(struct tty_struct *tty)
+{
+        clear_bit(TTY_LDISC, &tty->flags);
+        cancel_delayed_work(&tty->buf.work);
+        /*
+         * Wait for ->hangup_work and ->buf.work handlers to terminate
+         */
+        flush_scheduled_work();
+}
+
+/**
+ *      tty_ldisc_wait_idle     -       wait for the ldisc to become idle
+ *      @tty: tty to wait for
+ *
+ *      Wait for the line discipline to become idle. The discipline must
+ *      have been halted for this to guarantee it remains idle.
+ *
+ */
+
+static void tty_ldisc_wait_idle(struct tty_struct *tty)
+{
+        unsigned long flags;
+        spin_lock_irqsave(&tty_ldisc_lock, flags);
+        while (tty->ldisc.refcount) {
+                spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+                wait_event(tty_ldisc_wait, tty->ldisc.refcount == 0);
+                spin_lock_irqsave(&tty_ldisc_lock, flags);
+        }
+        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+}
+
+/**
  *      tty_set_ldisc           -       set line discipline
  *      @tty: the terminal to set
  *      @ldisc: the line discipline
@@ -636,6 +680,21 @@ int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
         return 0;
 }
 
+static void tty_ldisc_reinit(struct tty_struct *tty)
+{
+        struct tty_ldisc ld;
+
+        if (tty->ldisc.ops->close)
+                (tty->ldisc.ops->close)(tty);
+        tty_ldisc_put(tty->ldisc.ops);
+        /*
+         *      Switch the line discipline back
+         */
+        WARN_ON(tty_ldisc_get(N_TTY, &ld));
+        tty_ldisc_assign(tty, &ld);
+        tty_set_termios_ldisc(tty, N_TTY);
+}
+
 /**
  *      tty_ldisc_release               -       release line discipline
  *      @tty: tty being shut down
@@ -647,58 +706,34 @@ int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
 
 void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
 {
-        unsigned long flags;
-        struct tty_ldisc ld;
+
         /*
          * Prevent flush_to_ldisc() from rescheduling the work for later.  Then
          * kill any delayed work. As this is the final close it does not
          * race with the set_ldisc code path.
          */
-        clear_bit(TTY_LDISC, &tty->flags);
-        cancel_delayed_work(&tty->buf.work);
 
-        /*
-         * Wait for ->hangup_work and ->buf.work handlers to terminate
-         */
-
-        flush_scheduled_work();
+        tty_ldisc_halt(tty);
 
         /*
          * Wait for any short term users (we know they are just driver
          * side waiters as the file is closing so user count on the file
          * side is zero.
          */
-        spin_lock_irqsave(&tty_ldisc_lock, flags);
-        while (tty->ldisc.refcount) {
-                spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-                wait_event(tty_ldisc_wait, tty->ldisc.refcount == 0);
-                spin_lock_irqsave(&tty_ldisc_lock, flags);
-        }
-        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+
+        tty_ldisc_wait_idle(tty);
+
         /*
          * Shutdown the current line discipline, and reset it to N_TTY.
          *
          * FIXME: this MUST get fixed for the new reflocking
          */
-        if (tty->ldisc.ops->close)
-                (tty->ldisc.ops->close)(tty);
-        tty_ldisc_put(tty->ldisc.ops);
 
-        /*
-         *      Switch the line discipline back
-         */
-        WARN_ON(tty_ldisc_get(N_TTY, &ld));
-        tty_ldisc_assign(tty, &ld);
-        tty_set_termios_ldisc(tty, N_TTY);
+        tty_ldisc_reinit(tty);
         if (o_tty) {
                 /* FIXME: could o_tty be in setldisc here ? */
                 clear_bit(TTY_LDISC, &o_tty->flags);
-                if (o_tty->ldisc.ops->close)
-                        (o_tty->ldisc.ops->close)(o_tty);
-                tty_ldisc_put(o_tty->ldisc.ops);
-                WARN_ON(tty_ldisc_get(N_TTY, &ld));
-                tty_ldisc_assign(o_tty, &ld);
-                tty_set_termios_ldisc(o_tty, N_TTY);
+                tty_ldisc_reinit(o_tty);
         }
 }
 
diff --git a/include/linux/tty.h b/include/linux/tty.h
index bed5a3d40307..f9c13c83790c 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -428,6 +428,9 @@ extern struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
 extern void tty_release_dev(struct file *filp);
 extern int tty_init_termios(struct tty_struct *tty);
 
+extern struct tty_struct *tty_pair_get_tty(struct tty_struct *tty);
+extern struct tty_struct *tty_pair_get_pty(struct tty_struct *tty);
+
 extern struct mutex tty_mutex;
 
 extern void tty_write_unlock(struct tty_struct *tty);