v4.19.13 snapshot.
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
new file mode 100644
index 0000000..fc4c97c
--- /dev/null
+++ b/drivers/tty/tty_ldisc.c
@@ -0,0 +1,831 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/kmod.h>
+#include <linux/sched.h>
+#include <linux/interrupt.h>
+#include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/file.h>
+#include <linux/mm.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/poll.h>
+#include <linux/proc_fs.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/wait.h>
+#include <linux/bitops.h>
+#include <linux/seq_file.h>
+#include <linux/uaccess.h>
+#include <linux/ratelimit.h>
+
+#undef LDISC_DEBUG_HANGUP
+
+#ifdef LDISC_DEBUG_HANGUP
+#define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args)
+#else
+#define tty_ldisc_debug(tty, f, args...)
+#endif
+
+/* lockdep nested classes for tty->ldisc_sem */
+enum {
+ LDISC_SEM_NORMAL,
+ LDISC_SEM_OTHER,
+};
+
+
+/*
+ * 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_RAW_SPINLOCK(tty_ldiscs_lock);
+/* Line disc dispatch table */
+static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
+
+/**
+ * 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_ldiscs_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;
+
+ raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
+ tty_ldiscs[disc] = new_ldisc;
+ new_ldisc->num = disc;
+ new_ldisc->refcount = 0;
+ raw_spin_unlock_irqrestore(&tty_ldiscs_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_ldiscs_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;
+
+ raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
+ if (tty_ldiscs[disc]->refcount)
+ ret = -EBUSY;
+ else
+ tty_ldiscs[disc] = NULL;
+ raw_spin_unlock_irqrestore(&tty_ldiscs_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;
+
+ raw_spin_lock_irqsave(&tty_ldiscs_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;
+ }
+ }
+ raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
+ return ret;
+}
+
+static void put_ldops(struct tty_ldisc_ops *ldops)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
+ ldops->refcount--;
+ module_put(ldops->owner);
+ raw_spin_unlock_irqrestore(&tty_ldiscs_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: -EINVAL if the discipline index is not [N_TTY..NR_LDISCS] or
+ * if the discipline is not registered
+ * -EAGAIN if request_module() failed to load or register the
+ * the discipline
+ * -ENOMEM if allocation failure
+ *
+ * Otherwise, returns a pointer to the discipline and bumps the
+ * ref count
+ *
+ * Locking:
+ * takes tty_ldiscs_lock to guard against ldisc races
+ */
+
+static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, 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);
+ }
+
+ /*
+ * There is no way to handle allocation failure of only 16 bytes.
+ * Let's simplify error handling and save more memory.
+ */
+ ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
+ ld->ops = ldops;
+ ld->tty = tty;
+
+ return ld;
+}
+
+/**
+ * tty_ldisc_put - release the ldisc
+ *
+ * Complement of tty_ldisc_get().
+ */
+static void tty_ldisc_put(struct tty_ldisc *ld)
+{
+ if (WARN_ON_ONCE(!ld))
+ return;
+
+ put_ldops(ld->ops);
+ kfree(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;
+}
+
+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,
+};
+
+/**
+ * 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.
+ *
+ * Returns: NULL if the tty has been hungup and not re-opened with
+ * a new file descriptor, otherwise valid ldisc reference
+ *
+ * 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)
+ *
+ * Note: a file_operations routine (read/poll/write) should use this
+ * function to wait for any ldisc lifetime events to finish.
+ */
+
+struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
+{
+ struct tty_ldisc *ld;
+
+ ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
+ ld = tty->ldisc;
+ if (!ld)
+ ldsem_up_read(&tty->ldisc_sem);
+ 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.
+ */
+
+struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
+{
+ struct tty_ldisc *ld = NULL;
+
+ if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
+ ld = tty->ldisc;
+ if (!ld)
+ ldsem_up_read(&tty->ldisc_sem);
+ }
+ return ld;
+}
+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.
+ */
+
+void tty_ldisc_deref(struct tty_ldisc *ld)
+{
+ ldsem_up_read(&ld->tty->ldisc_sem);
+}
+EXPORT_SYMBOL_GPL(tty_ldisc_deref);
+
+
+static inline int
+__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
+{
+ return ldsem_down_write(&tty->ldisc_sem, timeout);
+}
+
+static inline int
+__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
+{
+ return ldsem_down_write_nested(&tty->ldisc_sem,
+ LDISC_SEM_OTHER, timeout);
+}
+
+static inline void __tty_ldisc_unlock(struct tty_struct *tty)
+{
+ ldsem_up_write(&tty->ldisc_sem);
+}
+
+int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
+{
+ int ret;
+
+ ret = __tty_ldisc_lock(tty, timeout);
+ if (!ret)
+ return -EBUSY;
+ set_bit(TTY_LDISC_HALTED, &tty->flags);
+ return 0;
+}
+
+void tty_ldisc_unlock(struct tty_struct *tty)
+{
+ clear_bit(TTY_LDISC_HALTED, &tty->flags);
+ __tty_ldisc_unlock(tty);
+}
+
+static int
+tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
+ unsigned long timeout)
+{
+ int ret;
+
+ if (tty < tty2) {
+ ret = __tty_ldisc_lock(tty, timeout);
+ if (ret) {
+ ret = __tty_ldisc_lock_nested(tty2, timeout);
+ if (!ret)
+ __tty_ldisc_unlock(tty);
+ }
+ } else {
+ /* if this is possible, it has lots of implications */
+ WARN_ON_ONCE(tty == tty2);
+ if (tty2 && tty != tty2) {
+ ret = __tty_ldisc_lock(tty2, timeout);
+ if (ret) {
+ ret = __tty_ldisc_lock_nested(tty, timeout);
+ if (!ret)
+ __tty_ldisc_unlock(tty2);
+ }
+ } else
+ ret = __tty_ldisc_lock(tty, timeout);
+ }
+
+ if (!ret)
+ return -EBUSY;
+
+ set_bit(TTY_LDISC_HALTED, &tty->flags);
+ if (tty2)
+ set_bit(TTY_LDISC_HALTED, &tty2->flags);
+ return 0;
+}
+
+static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
+{
+ tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
+}
+
+static void tty_ldisc_unlock_pair(struct tty_struct *tty,
+ struct tty_struct *tty2)
+{
+ __tty_ldisc_unlock(tty);
+ if (tty2)
+ __tty_ldisc_unlock(tty2);
+}
+
+/**
+ * tty_ldisc_flush - flush line discipline queue
+ * @tty: tty
+ *
+ * Flush the line discipline queue (if any) and the tty flip buffers
+ * for this tty.
+ */
+
+void tty_ldisc_flush(struct tty_struct *tty)
+{
+ struct tty_ldisc *ld = tty_ldisc_ref(tty);
+
+ tty_buffer_flush(tty, ld);
+ if (ld)
+ tty_ldisc_deref(ld);
+}
+EXPORT_SYMBOL_GPL(tty_ldisc_flush);
+
+/**
+ * tty_set_termios_ldisc - set ldisc field
+ * @tty: tty structure
+ * @disc: 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.
+ *
+ * The line discipline-related tty_struct fields are reset to
+ * prevent the ldisc driver from re-using stale information for
+ * the new ldisc instance.
+ *
+ * Locking: takes termios_rwsem
+ */
+
+static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
+{
+ down_write(&tty->termios_rwsem);
+ tty->termios.c_line = disc;
+ up_write(&tty->termios_rwsem);
+
+ tty->disc_data = NULL;
+ tty->receive_room = 0;
+}
+
+/**
+ * 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 */
+ ret = ld->ops->open(tty);
+ if (ret)
+ clear_bit(TTY_LDISC_OPEN, &tty->flags);
+
+ tty_ldisc_debug(tty, "%p: opened\n", ld);
+ 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_debug(tty, "%p: closed\n", ld);
+}
+
+/**
+ * tty_ldisc_failto - helper for ldisc failback
+ * @tty: tty to open the ldisc on
+ * @ld: ldisc we are trying to fail back to
+ *
+ * Helper to try and recover a tty when switching back to the old
+ * ldisc fails and we need something attached.
+ */
+
+static int tty_ldisc_failto(struct tty_struct *tty, int ld)
+{
+ struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
+ int r;
+
+ if (IS_ERR(disc))
+ return PTR_ERR(disc);
+ tty->ldisc = disc;
+ tty_set_termios_ldisc(tty, ld);
+ if ((r = tty_ldisc_open(tty, disc)) < 0)
+ tty_ldisc_put(disc);
+ return r;
+}
+
+/**
+ * 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)
+{
+ /* There is an outstanding reference here so this is safe */
+ if (tty_ldisc_failto(tty, old->ops->num) < 0) {
+ const char *name = tty_name(tty);
+
+ pr_warn("Falling back ldisc for %s.\n", name);
+ /* The traditional behaviour is to fall back to N_TTY, we
+ want to avoid falling back to N_NULL unless we have no
+ choice to avoid the risk of breaking anything */
+ if (tty_ldisc_failto(tty, N_TTY) < 0 &&
+ tty_ldisc_failto(tty, N_NULL) < 0)
+ panic("Couldn't open N_NULL ldisc for %s.", name);
+ }
+}
+
+/**
+ * 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.
+ */
+
+int tty_set_ldisc(struct tty_struct *tty, int disc)
+{
+ int retval;
+ struct tty_ldisc *old_ldisc, *new_ldisc;
+
+ new_ldisc = tty_ldisc_get(tty, disc);
+ if (IS_ERR(new_ldisc))
+ return PTR_ERR(new_ldisc);
+
+ tty_lock(tty);
+ retval = tty_ldisc_lock(tty, 5 * HZ);
+ if (retval)
+ goto err;
+
+ if (!tty->ldisc) {
+ retval = -EIO;
+ goto out;
+ }
+
+ /* Check the no-op case */
+ if (tty->ldisc->ops->num == disc)
+ goto out;
+
+ if (test_bit(TTY_HUPPED, &tty->flags)) {
+ /* We were raced by hangup */
+ retval = -EIO;
+ goto out;
+ }
+
+ old_ldisc = tty->ldisc;
+
+ /* Shutdown the old discipline. */
+ tty_ldisc_close(tty, old_ldisc);
+
+ /* Now set up the new line discipline. */
+ tty->ldisc = new_ldisc;
+ tty_set_termios_ldisc(tty, disc);
+
+ 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, old_ldisc);
+ }
+
+ if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
+ down_read(&tty->termios_rwsem);
+ tty->ops->set_ldisc(tty);
+ up_read(&tty->termios_rwsem);
+ }
+
+ /* At this point we hold a reference to the new ldisc and a
+ reference to the old ldisc, or we hold two references to
+ the old ldisc (if it was restored as part of error cleanup
+ above). In either case, releasing a single reference from
+ the old ldisc is correct. */
+ new_ldisc = old_ldisc;
+out:
+ tty_ldisc_unlock(tty);
+
+ /* Restart the work queue in case no characters kick it off. Safe if
+ already running */
+ tty_buffer_restart_work(tty->port);
+err:
+ tty_ldisc_put(new_ldisc); /* drop the extra reference */
+ tty_unlock(tty);
+ return retval;
+}
+EXPORT_SYMBOL_GPL(tty_set_ldisc);
+
+/**
+ * tty_ldisc_kill - teardown ldisc
+ * @tty: tty being released
+ *
+ * Perform final close of the ldisc and reset tty->ldisc
+ */
+static void tty_ldisc_kill(struct tty_struct *tty)
+{
+ if (!tty->ldisc)
+ return;
+ /*
+ * 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;
+}
+
+/**
+ * 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)
+{
+ down_write(&tty->termios_rwsem);
+ 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);
+ up_write(&tty->termios_rwsem);
+}
+
+
+/**
+ * tty_ldisc_reinit - reinitialise the tty ldisc
+ * @tty: tty to reinit
+ * @disc: line discipline to reinitialize
+ *
+ * Completely reinitialize the line discipline state, by closing the
+ * current instance, if there is one, and opening a new instance. If
+ * an error occurs opening the new non-N_TTY instance, the instance
+ * is dropped and tty->ldisc reset to NULL. The caller can then retry
+ * with N_TTY instead.
+ *
+ * Returns 0 if successful, otherwise error code < 0
+ */
+
+int tty_ldisc_reinit(struct tty_struct *tty, int disc)
+{
+ struct tty_ldisc *ld;
+ int retval;
+
+ ld = tty_ldisc_get(tty, disc);
+ if (IS_ERR(ld)) {
+ BUG_ON(disc == N_TTY);
+ return PTR_ERR(ld);
+ }
+
+ if (tty->ldisc) {
+ tty_ldisc_close(tty, tty->ldisc);
+ tty_ldisc_put(tty->ldisc);
+ }
+
+ /* switch the line discipline */
+ tty->ldisc = ld;
+ tty_set_termios_ldisc(tty, disc);
+ retval = tty_ldisc_open(tty, tty->ldisc);
+ if (retval) {
+ tty_ldisc_put(tty->ldisc);
+ tty->ldisc = NULL;
+ }
+ return retval;
+}
+
+/**
+ * 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, bool reinit)
+{
+ struct tty_ldisc *ld;
+
+ tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
+
+ ld = tty_ldisc_ref(tty);
+ if (ld != NULL) {
+ 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);
+ }
+
+ wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
+ wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
+
+ /*
+ * Shutdown the current line discipline, and reset it to
+ * N_TTY if need be.
+ *
+ * Avoid racing set_ldisc or tty_ldisc_release
+ */
+ tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
+
+ if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
+ tty_reset_termios(tty);
+
+ if (tty->ldisc) {
+ if (reinit) {
+ if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
+ tty_ldisc_reinit(tty, N_TTY) < 0)
+ WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
+ } else
+ tty_ldisc_kill(tty);
+ }
+ tty_ldisc_unlock(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)
+{
+ int retval = tty_ldisc_open(tty, tty->ldisc);
+ if (retval)
+ return retval;
+
+ if (o_tty) {
+ retval = tty_ldisc_open(o_tty, o_tty->ldisc);
+ if (retval) {
+ tty_ldisc_close(tty, tty->ldisc);
+ return retval;
+ }
+ }
+ return 0;
+}
+
+/**
+ * tty_ldisc_release - release line discipline
+ * @tty: tty being shut down (or one end of pty pair)
+ *
+ * Called during the final close of a tty or a pty pair in order to shut
+ * down the line discpline layer. On exit, each tty's ldisc is NULL.
+ */
+
+void tty_ldisc_release(struct tty_struct *tty)
+{
+ struct tty_struct *o_tty = tty->link;
+
+ /*
+ * Shutdown this line discipline. As this is the final close,
+ * it does not race with the set_ldisc code path.
+ */
+
+ tty_ldisc_lock_pair(tty, o_tty);
+ tty_ldisc_kill(tty);
+ if (o_tty)
+ tty_ldisc_kill(o_tty);
+ tty_ldisc_unlock_pair(tty, o_tty);
+
+ /* And the memory resources remaining (buffers, termios) will be
+ disposed of when the kref hits zero */
+
+ tty_ldisc_debug(tty, "released\n");
+}
+EXPORT_SYMBOL_GPL(tty_ldisc_release);
+
+/**
+ * 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.
+ */
+
+int tty_ldisc_init(struct tty_struct *tty)
+{
+ struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
+ if (IS_ERR(ld))
+ return PTR_ERR(ld);
+ tty->ldisc = ld;
+ return 0;
+}
+
+/**
+ * tty_ldisc_deinit - ldisc cleanup for new tty
+ * @tty: tty that was allocated recently
+ *
+ * The tty structure must not becompletely set up (tty_ldisc_setup) when
+ * this call is made.
+ */
+void tty_ldisc_deinit(struct tty_struct *tty)
+{
+ if (tty->ldisc)
+ tty_ldisc_put(tty->ldisc);
+ tty->ldisc = NULL;
+}