Merge branch 'kconfig_fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-next into kbuild/rc-fixes

1 files changed, 950 insertions, 0 deletions

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
new file mode 100644
index 000000000000..d8e96b005023
--- /dev/null
+++ b/drivers/tty/tty_ldisc.c
@@ -0,0 +1,950 @@
+#include <linux/types.h>
+#include <linux/major.h>
+#include <linux/errno.h>
+#include <linux/signal.h>
+#include <linux/fcntl.h>
+#include <linux/sched.h>
+#include <linux/interrupt.h>
+#include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/tty_flip.h>
+#include <linux/devpts_fs.h>
+#include <linux/file.h>
+#include <linux/console.h>
+#include <linux/timer.h>
+#include <linux/ctype.h>
+#include <linux/kd.h>
+#include <linux/mm.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/poll.h>
+#include <linux/proc_fs.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/wait.h>
+#include <linux/bitops.h>
+#include <linux/delay.h>
+#include <linux/seq_file.h>
+
+#include <linux/uaccess.h>
+#include <asm/system.h>
+
+#include <linux/kbd_kern.h>
+#include <linux/vt_kern.h>
+#include <linux/selection.h>
+
+#include <linux/smp_lock.h>     /* For the moment */
+
+#include <linux/kmod.h>
+#include <linux/nsproxy.h>
+
+/*
+ *      This guards the refcounted line discipline lists. The lock
+ *      must be taken with irqs off because there are hangup path
+ *      callers who will do ldisc lookups and cannot sleep.
+ */
+
+static DEFINE_SPINLOCK(tty_ldisc_lock);
+static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
+static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle);
+/* Line disc dispatch table */
+static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
+
+static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
+{
+        if (ld)
+                atomic_inc(&ld->users);
+        return ld;
+}
+
+static void put_ldisc(struct tty_ldisc *ld)
+{
+        unsigned long flags;
+
+        if (WARN_ON_ONCE(!ld))
+                return;
+
+        /*
+         * If this is the last user, free the ldisc, and
+         * release the ldisc ops.
+         *
+         * We really want an "atomic_dec_and_lock_irqsave()",
+         * but we don't have it, so this does it by hand.
+         */
+        local_irq_save(flags);
+        if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) {
+                struct tty_ldisc_ops *ldo = ld->ops;
+
+                ldo->refcount--;
+                module_put(ldo->owner);
+                spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+
+                kfree(ld);
+                return;
+        }
+        local_irq_restore(flags);
+        wake_up(&tty_ldisc_idle);
+}
+
+/**
+ *      tty_register_ldisc      -       install a line discipline
+ *      @disc: ldisc number
+ *      @new_ldisc: pointer to the ldisc object
+ *
+ *      Installs a new line discipline into the kernel. The discipline
+ *      is set up as unreferenced and then made available to the kernel
+ *      from this point onwards.
+ *
+ *      Locking:
+ *              takes tty_ldisc_lock to guard against ldisc races
+ */
+
+int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
+{
+        unsigned long flags;
+        int ret = 0;
+
+        if (disc < N_TTY || disc >= NR_LDISCS)
+                return -EINVAL;
+
+        spin_lock_irqsave(&tty_ldisc_lock, flags);
+        tty_ldiscs[disc] = new_ldisc;
+        new_ldisc->num = disc;
+        new_ldisc->refcount = 0;
+        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+
+        return ret;
+}
+EXPORT_SYMBOL(tty_register_ldisc);
+
+/**
+ *      tty_unregister_ldisc    -       unload a line discipline
+ *      @disc: ldisc number
+ *      @new_ldisc: pointer to the ldisc object
+ *
+ *      Remove a line discipline from the kernel providing it is not
+ *      currently in use.
+ *
+ *      Locking:
+ *              takes tty_ldisc_lock to guard against ldisc races
+ */
+
+int tty_unregister_ldisc(int disc)
+{
+        unsigned long flags;
+        int ret = 0;
+
+        if (disc < N_TTY || disc >= NR_LDISCS)
+                return -EINVAL;
+
+        spin_lock_irqsave(&tty_ldisc_lock, flags);
+        if (tty_ldiscs[disc]->refcount)
+                ret = -EBUSY;
+        else
+                tty_ldiscs[disc] = NULL;
+        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+
+        return ret;
+}
+EXPORT_SYMBOL(tty_unregister_ldisc);
+
+static struct tty_ldisc_ops *get_ldops(int disc)
+{
+        unsigned long flags;
+        struct tty_ldisc_ops *ldops, *ret;
+
+        spin_lock_irqsave(&tty_ldisc_lock, flags);
+        ret = ERR_PTR(-EINVAL);
+        ldops = tty_ldiscs[disc];
+        if (ldops) {
+                ret = ERR_PTR(-EAGAIN);
+                if (try_module_get(ldops->owner)) {
+                        ldops->refcount++;
+                        ret = ldops;
+                }
+        }
+        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+        return ret;
+}
+
+static void put_ldops(struct tty_ldisc_ops *ldops)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&tty_ldisc_lock, flags);
+        ldops->refcount--;
+        module_put(ldops->owner);
+        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+}
+
+/**
+ *      tty_ldisc_get           -       take a reference to an ldisc
+ *      @disc: ldisc number
+ *
+ *      Takes a reference to a line discipline. Deals with refcounts and
+ *      module locking counts. Returns NULL if the discipline is not available.
+ *      Returns a pointer to the discipline and bumps the ref count if it is
+ *      available
+ *
+ *      Locking:
+ *              takes tty_ldisc_lock to guard against ldisc races
+ */
+
+static struct tty_ldisc *tty_ldisc_get(int disc)
+{
+        struct tty_ldisc *ld;
+        struct tty_ldisc_ops *ldops;
+
+        if (disc < N_TTY || disc >= NR_LDISCS)
+                return ERR_PTR(-EINVAL);
+
+        /*
+         * Get the ldisc ops - we may need to request them to be loaded
+         * dynamically and try again.
+         */
+        ldops = get_ldops(disc);
+        if (IS_ERR(ldops)) {
+                request_module("tty-ldisc-%d", disc);
+                ldops = get_ldops(disc);
+                if (IS_ERR(ldops))
+                        return ERR_CAST(ldops);
+        }
+
+        ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
+        if (ld == NULL) {
+                put_ldops(ldops);
+                return ERR_PTR(-ENOMEM);
+        }
+
+        ld->ops = ldops;
+        atomic_set(&ld->users, 1);
+        return ld;
+}
+
+static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
+{
+        return (*pos < NR_LDISCS) ? pos : NULL;
+}
+
+static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
+{
+        (*pos)++;
+        return (*pos < NR_LDISCS) ? pos : NULL;
+}
+
+static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
+{
+}
+
+static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
+{
+        int i = *(loff_t *)v;
+        struct tty_ldisc_ops *ldops;
+
+        ldops = get_ldops(i);
+        if (IS_ERR(ldops))
+                return 0;
+        seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
+        put_ldops(ldops);
+        return 0;
+}
+
+static const struct seq_operations tty_ldiscs_seq_ops = {
+        .start  = tty_ldiscs_seq_start,
+        .next   = tty_ldiscs_seq_next,
+        .stop   = tty_ldiscs_seq_stop,
+        .show   = tty_ldiscs_seq_show,
+};
+
+static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
+{
+        return seq_open(file, &tty_ldiscs_seq_ops);
+}
+
+const struct file_operations tty_ldiscs_proc_fops = {
+        .owner          = THIS_MODULE,
+        .open           = proc_tty_ldiscs_open,
+        .read           = seq_read,
+        .llseek         = seq_lseek,
+        .release        = seq_release,
+};
+
+/**
+ *      tty_ldisc_assign        -       set ldisc on a tty
+ *      @tty: tty to assign
+ *      @ld: line discipline
+ *
+ *      Install an instance of a line discipline into a tty structure. The
+ *      ldisc must have a reference count above zero to ensure it remains.
+ *      The tty instance refcount starts at zero.
+ *
+ *      Locking:
+ *              Caller must hold references
+ */
+
+static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
+{
+        tty->ldisc = ld;
+}
+
+/**
+ *      tty_ldisc_try           -       internal helper
+ *      @tty: the tty
+ *
+ *      Make a single attempt to grab and bump the refcount on
+ *      the tty ldisc. Return 0 on failure or 1 on success. This is
+ *      used to implement both the waiting and non waiting versions
+ *      of tty_ldisc_ref
+ *
+ *      Locking: takes tty_ldisc_lock
+ */
+
+static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
+{
+        unsigned long flags;
+        struct tty_ldisc *ld;
+
+        spin_lock_irqsave(&tty_ldisc_lock, flags);
+        ld = NULL;
+        if (test_bit(TTY_LDISC, &tty->flags))
+                ld = get_ldisc(tty->ldisc);
+        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+        return ld;
+}
+
+/**
+ *      tty_ldisc_ref_wait      -       wait for the tty ldisc
+ *      @tty: tty device
+ *
+ *      Dereference the line discipline for the terminal and take a
+ *      reference to it. If the line discipline is in flux then
+ *      wait patiently until it changes.
+ *
+ *      Note: Must not be called from an IRQ/timer context. The caller
+ *      must also be careful not to hold other locks that will deadlock
+ *      against a discipline change, such as an existing ldisc reference
+ *      (which we check for)
+ *
+ *      Locking: call functions take tty_ldisc_lock
+ */
+
+struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
+{
+        struct tty_ldisc *ld;
+
+        /* wait_event is a macro */
+        wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
+        return ld;
+}
+EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
+
+/**
+ *      tty_ldisc_ref           -       get the tty ldisc
+ *      @tty: tty device
+ *
+ *      Dereference the line discipline for the terminal and take a
+ *      reference to it. If the line discipline is in flux then
+ *      return NULL. Can be called from IRQ and timer functions.
+ *
+ *      Locking: called functions take tty_ldisc_lock
+ */
+
+struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
+{
+        return tty_ldisc_try(tty);
+}
+EXPORT_SYMBOL_GPL(tty_ldisc_ref);
+
+/**
+ *      tty_ldisc_deref         -       free a tty ldisc reference
+ *      @ld: reference to free up
+ *
+ *      Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
+ *      be called in IRQ context.
+ *
+ *      Locking: takes tty_ldisc_lock
+ */
+
+void tty_ldisc_deref(struct tty_ldisc *ld)
+{
+        put_ldisc(ld);
+}
+EXPORT_SYMBOL_GPL(tty_ldisc_deref);
+
+static inline void tty_ldisc_put(struct tty_ldisc *ld)
+{
+        put_ldisc(ld);
+}
+
+/**
+ *      tty_ldisc_enable        -       allow ldisc use
+ *      @tty: terminal to activate ldisc on
+ *
+ *      Set the TTY_LDISC flag when the line discipline can be called
+ *      again. Do necessary wakeups for existing sleepers. Clear the LDISC
+ *      changing flag to indicate any ldisc change is now over.
+ *
+ *      Note: nobody should set the TTY_LDISC bit except via this function.
+ *      Clearing directly is allowed.
+ */
+
+void tty_ldisc_enable(struct tty_struct *tty)
+{
+        set_bit(TTY_LDISC, &tty->flags);
+        clear_bit(TTY_LDISC_CHANGING, &tty->flags);
+        wake_up(&tty_ldisc_wait);
+}
+
+/**
+ *      tty_ldisc_flush -       flush line discipline queue
+ *      @tty: tty
+ *
+ *      Flush the line discipline queue (if any) for this tty. If there
+ *      is no line discipline active this is a no-op.
+ */
+
+void tty_ldisc_flush(struct tty_struct *tty)
+{
+        struct tty_ldisc *ld = tty_ldisc_ref(tty);
+        if (ld) {
+                if (ld->ops->flush_buffer)
+                        ld->ops->flush_buffer(tty);
+                tty_ldisc_deref(ld);
+        }
+        tty_buffer_flush(tty);
+}
+EXPORT_SYMBOL_GPL(tty_ldisc_flush);
+
+/**
+ *      tty_set_termios_ldisc           -       set ldisc field
+ *      @tty: tty structure
+ *      @num: line discipline number
+ *
+ *      This is probably overkill for real world processors but
+ *      they are not on hot paths so a little discipline won't do
+ *      any harm.
+ *
+ *      Locking: takes termios_mutex
+ */
+
+static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
+{
+        mutex_lock(&tty->termios_mutex);
+        tty->termios->c_line = num;
+        mutex_unlock(&tty->termios_mutex);
+}
+
+/**
+ *      tty_ldisc_open          -       open a line discipline
+ *      @tty: tty we are opening the ldisc on
+ *      @ld: discipline to open
+ *
+ *      A helper opening method. Also a convenient debugging and check
+ *      point.
+ *
+ *      Locking: always called with BTM already held.
+ */
+
+static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
+{
+        WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
+        if (ld->ops->open) {
+                int ret;
+                /* BTM here locks versus a hangup event */
+                WARN_ON(!tty_locked());
+                ret = ld->ops->open(tty);
+                return ret;
+        }
+        return 0;
+}
+
+/**
+ *      tty_ldisc_close         -       close a line discipline
+ *      @tty: tty we are opening the ldisc on
+ *      @ld: discipline to close
+ *
+ *      A helper close method. Also a convenient debugging and check
+ *      point.
+ */
+
+static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
+{
+        WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
+        clear_bit(TTY_LDISC_OPEN, &tty->flags);
+        if (ld->ops->close)
+                ld->ops->close(tty);
+}
+
+/**
+ *      tty_ldisc_restore       -       helper for tty ldisc change
+ *      @tty: tty to recover
+ *      @old: previous ldisc
+ *
+ *      Restore the previous line discipline or N_TTY when a line discipline
+ *      change fails due to an open error
+ */
+
+static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
+{
+        char buf[64];
+        struct tty_ldisc *new_ldisc;
+        int r;
+
+        /* There is an outstanding reference here so this is safe */
+        old = tty_ldisc_get(old->ops->num);
+        WARN_ON(IS_ERR(old));
+        tty_ldisc_assign(tty, old);
+        tty_set_termios_ldisc(tty, old->ops->num);
+        if (tty_ldisc_open(tty, old) < 0) {
+                tty_ldisc_put(old);
+                /* This driver is always present */
+                new_ldisc = tty_ldisc_get(N_TTY);
+                if (IS_ERR(new_ldisc))
+                        panic("n_tty: get");
+                tty_ldisc_assign(tty, new_ldisc);
+                tty_set_termios_ldisc(tty, N_TTY);
+                r = tty_ldisc_open(tty, new_ldisc);
+                if (r < 0)
+                        panic("Couldn't open N_TTY ldisc for "
+                              "%s --- error %d.",
+                              tty_name(tty, buf), r);
+        }
+}
+
+/**
+ *      tty_ldisc_halt          -       shut down 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.
+ *
+ *      You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
+ *      in order to make sure any currently executing ldisc work is also
+ *      flushed.
+ */
+
+static int tty_ldisc_halt(struct tty_struct *tty)
+{
+        clear_bit(TTY_LDISC, &tty->flags);
+        return cancel_delayed_work_sync(&tty->buf.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 int tty_ldisc_wait_idle(struct tty_struct *tty)
+{
+        int ret;
+        ret = wait_event_interruptible_timeout(tty_ldisc_idle,
+                        atomic_read(&tty->ldisc->users) == 1, 5 * HZ);
+        if (ret < 0)
+                return ret;
+        return ret > 0 ? 0 : -EBUSY;
+}
+
+/**
+ *      tty_set_ldisc           -       set line discipline
+ *      @tty: the terminal to set
+ *      @ldisc: the line discipline
+ *
+ *      Set the discipline of a tty line. Must be called from a process
+ *      context. The ldisc change logic has to protect itself against any
+ *      overlapping ldisc change (including on the other end of pty pairs),
+ *      the close of one side of a tty/pty pair, and eventually hangup.
+ *
+ *      Locking: takes tty_ldisc_lock, termios_mutex
+ */
+
+int tty_set_ldisc(struct tty_struct *tty, int ldisc)
+{
+        int retval;
+        struct tty_ldisc *o_ldisc, *new_ldisc;
+        int work, o_work = 0;
+        struct tty_struct *o_tty;
+
+        new_ldisc = tty_ldisc_get(ldisc);
+        if (IS_ERR(new_ldisc))
+                return PTR_ERR(new_ldisc);
+
+        tty_lock();
+        /*
+         *      We need to look at the tty locking here for pty/tty pairs
+         *      when both sides try to change in parallel.
+         */
+
+        o_tty = tty->link;      /* o_tty is the pty side or NULL */
+
+
+        /*
+         *      Check the no-op case
+         */
+
+        if (tty->ldisc->ops->num == ldisc) {
+                tty_unlock();
+                tty_ldisc_put(new_ldisc);
+                return 0;
+        }
+
+        tty_unlock();
+        /*
+         *      Problem: What do we do if this blocks ?
+         *      We could deadlock here
+         */
+
+        tty_wait_until_sent(tty, 0);
+
+        tty_lock();
+        mutex_lock(&tty->ldisc_mutex);
+
+        /*
+         *      We could be midstream of another ldisc change which has
+         *      dropped the lock during processing. If so we need to wait.
+         */
+
+        while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
+                mutex_unlock(&tty->ldisc_mutex);
+                tty_unlock();
+                wait_event(tty_ldisc_wait,
+                        test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
+                tty_lock();
+                mutex_lock(&tty->ldisc_mutex);
+        }
+
+        set_bit(TTY_LDISC_CHANGING, &tty->flags);
+
+        /*
+         *      No more input please, we are switching. The new ldisc
+         *      will update this value in the ldisc open function
+         */
+
+        tty->receive_room = 0;
+
+        o_ldisc = tty->ldisc;
+
+        tty_unlock();
+        /*
+         *      Make sure we don't change while someone holds a
+         *      reference to the line discipline. The TTY_LDISC bit
+         *      prevents anyone taking a reference once it is clear.
+         *      We need the lock to avoid racing reference takers.
+         *
+         *      We must clear the TTY_LDISC bit here to avoid a livelock
+         *      with a userspace app continually trying to use the tty in
+         *      parallel to the change and re-referencing the tty.
+         */
+
+        work = tty_ldisc_halt(tty);
+        if (o_tty)
+                o_work = tty_ldisc_halt(o_tty);
+
+        /*
+         * Wait for ->hangup_work and ->buf.work handlers to terminate.
+         * We must drop the mutex here in case a hangup is also in process.
+         */
+
+        mutex_unlock(&tty->ldisc_mutex);
+
+        flush_scheduled_work();
+
+        retval = tty_ldisc_wait_idle(tty);
+
+        tty_lock();
+        mutex_lock(&tty->ldisc_mutex);
+
+        /* handle wait idle failure locked */
+        if (retval) {
+                tty_ldisc_put(new_ldisc);
+                goto enable;
+        }
+
+        if (test_bit(TTY_HUPPED, &tty->flags)) {
+                /* We were raced by the hangup method. It will have stomped
+                   the ldisc data and closed the ldisc down */
+                clear_bit(TTY_LDISC_CHANGING, &tty->flags);
+                mutex_unlock(&tty->ldisc_mutex);
+                tty_ldisc_put(new_ldisc);
+                tty_unlock();
+                return -EIO;
+        }
+
+        /* Shutdown the current discipline. */
+        tty_ldisc_close(tty, o_ldisc);
+
+        /* Now set up the new line discipline. */
+        tty_ldisc_assign(tty, new_ldisc);
+        tty_set_termios_ldisc(tty, ldisc);
+
+        retval = tty_ldisc_open(tty, new_ldisc);
+        if (retval < 0) {
+                /* Back to the old one or N_TTY if we can't */
+                tty_ldisc_put(new_ldisc);
+                tty_ldisc_restore(tty, o_ldisc);
+        }
+
+        /* At this point we hold a reference to the new ldisc and a
+           a reference to the old ldisc. If we ended up flipping back
+           to the existing ldisc we have two references to it */
+
+        if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
+                tty->ops->set_ldisc(tty);
+
+        tty_ldisc_put(o_ldisc);
+
+enable:
+        /*
+         *      Allow ldisc referencing to occur again
+         */
+
+        tty_ldisc_enable(tty);
+        if (o_tty)
+                tty_ldisc_enable(o_tty);
+
+        /* Restart the work queue in case no characters kick it off. Safe if
+           already running */
+        if (work)
+                schedule_delayed_work(&tty->buf.work, 1);
+        if (o_work)
+                schedule_delayed_work(&o_tty->buf.work, 1);
+        mutex_unlock(&tty->ldisc_mutex);
+        tty_unlock();
+        return retval;
+}
+
+/**
+ *      tty_reset_termios       -       reset terminal state
+ *      @tty: tty to reset
+ *
+ *      Restore a terminal to the driver default state.
+ */
+
+static void tty_reset_termios(struct tty_struct *tty)
+{
+        mutex_lock(&tty->termios_mutex);
+        *tty->termios = tty->driver->init_termios;
+        tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
+        tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
+        mutex_unlock(&tty->termios_mutex);
+}
+
+
+/**
+ *      tty_ldisc_reinit        -       reinitialise the tty ldisc
+ *      @tty: tty to reinit
+ *      @ldisc: line discipline to reinitialize
+ *
+ *      Switch the tty to a line discipline and leave the ldisc
+ *      state closed
+ */
+
+static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
+{
+        struct tty_ldisc *ld = tty_ldisc_get(ldisc);
+
+        if (IS_ERR(ld))
+                return -1;
+
+        tty_ldisc_close(tty, tty->ldisc);
+        tty_ldisc_put(tty->ldisc);
+        tty->ldisc = NULL;
+        /*
+         *      Switch the line discipline back
+         */
+        tty_ldisc_assign(tty, ld);
+        tty_set_termios_ldisc(tty, ldisc);
+
+        return 0;
+}
+
+/**
+ *      tty_ldisc_hangup                -       hangup ldisc reset
+ *      @tty: tty being hung up
+ *
+ *      Some tty devices reset their termios when they receive a hangup
+ *      event. In that situation we must also switch back to N_TTY properly
+ *      before we reset the termios data.
+ *
+ *      Locking: We can take the ldisc mutex as the rest of the code is
+ *      careful to allow for this.
+ *
+ *      In the pty pair case this occurs in the close() path of the
+ *      tty itself so we must be careful about locking rules.
+ */
+
+void tty_ldisc_hangup(struct tty_struct *tty)
+{
+        struct tty_ldisc *ld;
+        int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
+        int err = 0;
+
+        /*
+         * FIXME! What are the locking issues here? This may me overdoing
+         * things... This question is especially important now that we've
+         * removed the irqlock.
+         */
+        ld = tty_ldisc_ref(tty);
+        if (ld != NULL) {
+                /* We may have no line discipline at this point */
+                if (ld->ops->flush_buffer)
+                        ld->ops->flush_buffer(tty);
+                tty_driver_flush_buffer(tty);
+                if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
+                    ld->ops->write_wakeup)
+                        ld->ops->write_wakeup(tty);
+                if (ld->ops->hangup)
+                        ld->ops->hangup(tty);
+                tty_ldisc_deref(ld);
+        }
+        /*
+         * FIXME: Once we trust the LDISC code better we can wait here for
+         * ldisc completion and fix the driver call race
+         */
+        wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
+        wake_up_interruptible_poll(&tty->read_wait, POLLIN);
+        /*
+         * Shutdown the current line discipline, and reset it to
+         * N_TTY if need be.
+         *
+         * Avoid racing set_ldisc or tty_ldisc_release
+         */
+        mutex_lock(&tty->ldisc_mutex);
+
+        /*
+         * this is like tty_ldisc_halt, but we need to give up
+         * the BTM before calling cancel_delayed_work_sync,
+         * which may need to wait for another function taking the BTM
+         */
+        clear_bit(TTY_LDISC, &tty->flags);
+        tty_unlock();
+        cancel_delayed_work_sync(&tty->buf.work);
+        mutex_unlock(&tty->ldisc_mutex);
+
+        tty_lock();
+        mutex_lock(&tty->ldisc_mutex);
+
+        /* At this point we have a closed ldisc and we want to
+           reopen it. We could defer this to the next open but
+           it means auditing a lot of other paths so this is
+           a FIXME */
+        if (tty->ldisc) {       /* Not yet closed */
+                if (reset == 0) {
+
+                        if (!tty_ldisc_reinit(tty, tty->termios->c_line))
+                                err = tty_ldisc_open(tty, tty->ldisc);
+                        else
+                                err = 1;
+                }
+                /* If the re-open fails or we reset then go to N_TTY. The
+                   N_TTY open cannot fail */
+                if (reset || err) {
+                        BUG_ON(tty_ldisc_reinit(tty, N_TTY));
+                        WARN_ON(tty_ldisc_open(tty, tty->ldisc));
+                }
+                tty_ldisc_enable(tty);
+        }
+        mutex_unlock(&tty->ldisc_mutex);
+        if (reset)
+                tty_reset_termios(tty);
+}
+
+/**
+ *      tty_ldisc_setup                 -       open line discipline
+ *      @tty: tty being shut down
+ *      @o_tty: pair tty for pty/tty pairs
+ *
+ *      Called during the initial open of a tty/pty pair in order to set up the
+ *      line disciplines and bind them to the tty. This has no locking issues
+ *      as the device isn't yet active.
+ */
+
+int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
+{
+        struct tty_ldisc *ld = tty->ldisc;
+        int retval;
+
+        retval = tty_ldisc_open(tty, ld);
+        if (retval)
+                return retval;
+
+        if (o_tty) {
+                retval = tty_ldisc_open(o_tty, o_tty->ldisc);
+                if (retval) {
+                        tty_ldisc_close(tty, ld);
+                        return retval;
+                }
+                tty_ldisc_enable(o_tty);
+        }
+        tty_ldisc_enable(tty);
+        return 0;
+}
+/**
+ *      tty_ldisc_release               -       release line discipline
+ *      @tty: tty being shut down
+ *      @o_tty: pair tty for pty/tty pairs
+ *
+ *      Called during the final close of a tty/pty pair in order to shut down
+ *      the line discpline layer. On exit the ldisc assigned is N_TTY and the
+ *      ldisc has not been opened.
+ */
+
+void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
+{
+        /*
+         * 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.
+         */
+
+        tty_unlock();
+        tty_ldisc_halt(tty);
+        flush_scheduled_work();
+        tty_lock();
+
+        mutex_lock(&tty->ldisc_mutex);
+        /*
+         * Now kill off the ldisc
+         */
+        tty_ldisc_close(tty, tty->ldisc);
+        tty_ldisc_put(tty->ldisc);
+        /* Force an oops if we mess this up */
+        tty->ldisc = NULL;
+
+        /* Ensure the next open requests the N_TTY ldisc */
+        tty_set_termios_ldisc(tty, N_TTY);
+        mutex_unlock(&tty->ldisc_mutex);
+
+        /* This will need doing differently if we need to lock */
+        if (o_tty)
+                tty_ldisc_release(o_tty, NULL);
+
+        /* And the memory resources remaining (buffers, termios) will be
+           disposed of when the kref hits zero */
+}
+
+/**
+ *      tty_ldisc_init          -       ldisc setup for new tty
+ *      @tty: tty being allocated
+ *
+ *      Set up the line discipline objects for a newly allocated tty. Note that
+ *      the tty structure is not completely set up when this call is made.
+ */
+
+void tty_ldisc_init(struct tty_struct *tty)
+{
+        struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
+        if (IS_ERR(ld))
+                panic("n_tty: init_tty");
+        tty_ldisc_assign(tty, ld);
+}
+
+void tty_ldisc_begin(void)
+{
+        /* Setup the default TTY line discipline. */
+        (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
+}