Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 947 insertions, 0 deletions

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
new file mode 100644
index 000000000..07394fdaf
--- /dev/null
+++ b/drivers/tty/pty.c
@@ -0,0 +1,947 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ *
+ *  Added support for a Unix98-style ptmx device.
+ *    -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/interrupt.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/fcntl.h>
+#include <linux/sched/signal.h>
+#include <linux/string.h>
+#include <linux/major.h>
+#include <linux/mm.h>
+#include <linux/init.h>
+#include <linux/device.h>
+#include <linux/uaccess.h>
+#include <linux/bitops.h>
+#include <linux/devpts_fs.h>
+#include <linux/slab.h>
+#include <linux/mutex.h>
+#include <linux/poll.h>
+#include <linux/mount.h>
+#include <linux/file.h>
+#include <linux/ioctl.h>
+#include <linux/compat.h>
+#include "tty.h"
+
+#undef TTY_DEBUG_HANGUP
+#ifdef TTY_DEBUG_HANGUP
+# define tty_debug_hangup(tty, f, args...)	tty_debug(tty, f, ##args)
+#else
+# define tty_debug_hangup(tty, f, args...)	do {} while (0)
+#endif
+
+#ifdef CONFIG_UNIX98_PTYS
+static struct tty_driver *ptm_driver;
+static struct tty_driver *pts_driver;
+static DEFINE_MUTEX(devpts_mutex);
+#endif
+
+static void pty_close(struct tty_struct *tty, struct file *filp)
+{
+	if (tty->driver->subtype == PTY_TYPE_MASTER)
+		WARN_ON(tty->count > 1);
+	else {
+		if (tty_io_error(tty))
+			return;
+		if (tty->count > 2)
+			return;
+	}
+	set_bit(TTY_IO_ERROR, &tty->flags);
+	wake_up_interruptible(&tty->read_wait);
+	wake_up_interruptible(&tty->write_wait);
+	spin_lock_irq(&tty->ctrl.lock);
+	tty->ctrl.packet = false;
+	spin_unlock_irq(&tty->ctrl.lock);
+	/* Review - krefs on tty_link ?? */
+	if (!tty->link)
+		return;
+	set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
+	wake_up_interruptible(&tty->link->read_wait);
+	wake_up_interruptible(&tty->link->write_wait);
+	if (tty->driver->subtype == PTY_TYPE_MASTER) {
+		set_bit(TTY_OTHER_CLOSED, &tty->flags);
+#ifdef CONFIG_UNIX98_PTYS
+		if (tty->driver == ptm_driver) {
+			mutex_lock(&devpts_mutex);
+			if (tty->link->driver_data)
+				devpts_pty_kill(tty->link->driver_data);
+			mutex_unlock(&devpts_mutex);
+		}
+#endif
+		tty_vhangup(tty->link);
+	}
+}
+
+/*
+ * The unthrottle routine is called by the line discipline to signal
+ * that it can receive more characters.  For PTY's, the TTY_THROTTLED
+ * flag is always set, to force the line discipline to always call the
+ * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
+ * characters in the queue.  This is necessary since each time this
+ * happens, we need to wake up any sleeping processes that could be
+ * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
+ * for the pty buffer to be drained.
+ */
+static void pty_unthrottle(struct tty_struct *tty)
+{
+	tty_wakeup(tty->link);
+	set_bit(TTY_THROTTLED, &tty->flags);
+}
+
+/**
+ *	pty_write		-	write to a pty
+ *	@tty: the tty we write from
+ *	@buf: kernel buffer of data
+ *	@c: bytes to write
+ *
+ *	Our "hardware" write method. Data is coming from the ldisc which
+ *	may be in a non sleeping state. We simply throw this at the other
+ *	end of the link as if we were an IRQ handler receiving stuff for
+ *	the other side of the pty/tty pair.
+ */
+
+static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
+{
+	struct tty_struct *to = tty->link;
+
+	if (tty->flow.stopped || !c)
+		return 0;
+
+	return tty_insert_flip_string_and_push_buffer(to->port, buf, c);
+}
+
+/**
+ *	pty_write_room	-	write space
+ *	@tty: tty we are writing from
+ *
+ *	Report how many bytes the ldisc can send into the queue for
+ *	the other device.
+ */
+
+static unsigned int pty_write_room(struct tty_struct *tty)
+{
+	if (tty->flow.stopped)
+		return 0;
+	return tty_buffer_space_avail(tty->link->port);
+}
+
+/* Set the lock flag on a pty */
+static int pty_set_lock(struct tty_struct *tty, int __user *arg)
+{
+	int val;
+
+	if (get_user(val, arg))
+		return -EFAULT;
+	if (val)
+		set_bit(TTY_PTY_LOCK, &tty->flags);
+	else
+		clear_bit(TTY_PTY_LOCK, &tty->flags);
+	return 0;
+}
+
+static int pty_get_lock(struct tty_struct *tty, int __user *arg)
+{
+	int locked = test_bit(TTY_PTY_LOCK, &tty->flags);
+
+	return put_user(locked, arg);
+}
+
+/* Set the packet mode on a pty */
+static int pty_set_pktmode(struct tty_struct *tty, int __user *arg)
+{
+	int pktmode;
+
+	if (get_user(pktmode, arg))
+		return -EFAULT;
+
+	spin_lock_irq(&tty->ctrl.lock);
+	if (pktmode) {
+		if (!tty->ctrl.packet) {
+			tty->link->ctrl.pktstatus = 0;
+			smp_mb();
+			tty->ctrl.packet = true;
+		}
+	} else
+		tty->ctrl.packet = false;
+	spin_unlock_irq(&tty->ctrl.lock);
+
+	return 0;
+}
+
+/* Get the packet mode of a pty */
+static int pty_get_pktmode(struct tty_struct *tty, int __user *arg)
+{
+	int pktmode = tty->ctrl.packet;
+
+	return put_user(pktmode, arg);
+}
+
+/* Send a signal to the slave */
+static int pty_signal(struct tty_struct *tty, int sig)
+{
+	struct pid *pgrp;
+
+	if (sig != SIGINT && sig != SIGQUIT && sig != SIGTSTP)
+		return -EINVAL;
+
+	if (tty->link) {
+		pgrp = tty_get_pgrp(tty->link);
+		if (pgrp)
+			kill_pgrp(pgrp, sig, 1);
+		put_pid(pgrp);
+	}
+	return 0;
+}
+
+static void pty_flush_buffer(struct tty_struct *tty)
+{
+	struct tty_struct *to = tty->link;
+
+	if (!to)
+		return;
+
+	tty_buffer_flush(to, NULL);
+	if (to->ctrl.packet) {
+		spin_lock_irq(&tty->ctrl.lock);
+		tty->ctrl.pktstatus |= TIOCPKT_FLUSHWRITE;
+		wake_up_interruptible(&to->read_wait);
+		spin_unlock_irq(&tty->ctrl.lock);
+	}
+}
+
+static int pty_open(struct tty_struct *tty, struct file *filp)
+{
+	if (!tty || !tty->link)
+		return -ENODEV;
+
+	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
+		goto out;
+	if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
+		goto out;
+	if (tty->driver->subtype == PTY_TYPE_SLAVE && tty->link->count != 1)
+		goto out;
+
+	clear_bit(TTY_IO_ERROR, &tty->flags);
+	clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
+	set_bit(TTY_THROTTLED, &tty->flags);
+	return 0;
+
+out:
+	set_bit(TTY_IO_ERROR, &tty->flags);
+	return -EIO;
+}
+
+static void pty_set_termios(struct tty_struct *tty,
+			    const struct ktermios *old_termios)
+{
+	/* See if packet mode change of state. */
+	if (tty->link && tty->link->ctrl.packet) {
+		int extproc = (old_termios->c_lflag & EXTPROC) | L_EXTPROC(tty);
+		int old_flow = ((old_termios->c_iflag & IXON) &&
+				(old_termios->c_cc[VSTOP] == '\023') &&
+				(old_termios->c_cc[VSTART] == '\021'));
+		int new_flow = (I_IXON(tty) &&
+				STOP_CHAR(tty) == '\023' &&
+				START_CHAR(tty) == '\021');
+		if ((old_flow != new_flow) || extproc) {
+			spin_lock_irq(&tty->ctrl.lock);
+			if (old_flow != new_flow) {
+				tty->ctrl.pktstatus &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
+				if (new_flow)
+					tty->ctrl.pktstatus |= TIOCPKT_DOSTOP;
+				else
+					tty->ctrl.pktstatus |= TIOCPKT_NOSTOP;
+			}
+			if (extproc)
+				tty->ctrl.pktstatus |= TIOCPKT_IOCTL;
+			spin_unlock_irq(&tty->ctrl.lock);
+			wake_up_interruptible(&tty->link->read_wait);
+		}
+	}
+
+	tty->termios.c_cflag &= ~(CSIZE | PARENB);
+	tty->termios.c_cflag |= (CS8 | CREAD);
+}
+
+/**
+ *	pty_resize		-	resize event
+ *	@tty: tty being resized
+ *	@ws: window size being set.
+ *
+ *	Update the termios variables and send the necessary signals to
+ *	peform a terminal resize correctly
+ */
+
+static int pty_resize(struct tty_struct *tty,  struct winsize *ws)
+{
+	struct pid *pgrp, *rpgrp;
+	struct tty_struct *pty = tty->link;
+
+	/* For a PTY we need to lock the tty side */
+	mutex_lock(&tty->winsize_mutex);
+	if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
+		goto done;
+
+	/* Signal the foreground process group of both ptys */
+	pgrp = tty_get_pgrp(tty);
+	rpgrp = tty_get_pgrp(pty);
+
+	if (pgrp)
+		kill_pgrp(pgrp, SIGWINCH, 1);
+	if (rpgrp != pgrp && rpgrp)
+		kill_pgrp(rpgrp, SIGWINCH, 1);
+
+	put_pid(pgrp);
+	put_pid(rpgrp);
+
+	tty->winsize = *ws;
+	pty->winsize = *ws;	/* Never used so will go away soon */
+done:
+	mutex_unlock(&tty->winsize_mutex);
+	return 0;
+}
+
+/**
+ *	pty_start - start() handler
+ *	pty_stop  - stop() handler
+ *	@tty: tty being flow-controlled
+ *
+ *	Propagates the TIOCPKT status to the master pty.
+ *
+ *	NB: only the master pty can be in packet mode so only the slave
+ *	    needs start()/stop() handlers
+ */
+static void pty_start(struct tty_struct *tty)
+{
+	unsigned long flags;
+
+	if (tty->link && tty->link->ctrl.packet) {
+		spin_lock_irqsave(&tty->ctrl.lock, flags);
+		tty->ctrl.pktstatus &= ~TIOCPKT_STOP;
+		tty->ctrl.pktstatus |= TIOCPKT_START;
+		spin_unlock_irqrestore(&tty->ctrl.lock, flags);
+		wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
+	}
+}
+
+static void pty_stop(struct tty_struct *tty)
+{
+	unsigned long flags;
+
+	if (tty->link && tty->link->ctrl.packet) {
+		spin_lock_irqsave(&tty->ctrl.lock, flags);
+		tty->ctrl.pktstatus &= ~TIOCPKT_START;
+		tty->ctrl.pktstatus |= TIOCPKT_STOP;
+		spin_unlock_irqrestore(&tty->ctrl.lock, flags);
+		wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
+	}
+}
+
+/**
+ *	pty_common_install		-	set up the pty pair
+ *	@driver: the pty driver
+ *	@tty: the tty being instantiated
+ *	@legacy: true if this is BSD style
+ *
+ *	Perform the initial set up for the tty/pty pair. Called from the
+ *	tty layer when the port is first opened.
+ *
+ *	Locking: the caller must hold the tty_mutex
+ */
+static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
+		bool legacy)
+{
+	struct tty_struct *o_tty;
+	struct tty_port *ports[2];
+	int idx = tty->index;
+	int retval = -ENOMEM;
+
+	/* Opening the slave first has always returned -EIO */
+	if (driver->subtype != PTY_TYPE_MASTER)
+		return -EIO;
+
+	ports[0] = kmalloc(sizeof **ports, GFP_KERNEL);
+	ports[1] = kmalloc(sizeof **ports, GFP_KERNEL);
+	if (!ports[0] || !ports[1])
+		goto err;
+	if (!try_module_get(driver->other->owner)) {
+		/* This cannot in fact currently happen */
+		goto err;
+	}
+	o_tty = alloc_tty_struct(driver->other, idx);
+	if (!o_tty)
+		goto err_put_module;
+
+	tty_set_lock_subclass(o_tty);
+	lockdep_set_subclass(&o_tty->termios_rwsem, TTY_LOCK_SLAVE);
+
+	if (legacy) {
+		/* We always use new tty termios data so we can do this
+		   the easy way .. */
+		tty_init_termios(tty);
+		tty_init_termios(o_tty);
+
+		driver->other->ttys[idx] = o_tty;
+		driver->ttys[idx] = tty;
+	} else {
+		memset(&tty->termios_locked, 0, sizeof(tty->termios_locked));
+		tty->termios = driver->init_termios;
+		memset(&o_tty->termios_locked, 0, sizeof(tty->termios_locked));
+		o_tty->termios = driver->other->init_termios;
+	}
+
+	/*
+	 * Everything allocated ... set up the o_tty structure.
+	 */
+	tty_driver_kref_get(driver->other);
+	/* Establish the links in both directions */
+	tty->link   = o_tty;
+	o_tty->link = tty;
+	tty_port_init(ports[0]);
+	tty_port_init(ports[1]);
+	tty_buffer_set_limit(ports[0], 8192);
+	tty_buffer_set_limit(ports[1], 8192);
+	o_tty->port = ports[0];
+	tty->port = ports[1];
+	o_tty->port->itty = o_tty;
+
+	tty_buffer_set_lock_subclass(o_tty->port);
+
+	tty_driver_kref_get(driver);
+	tty->count++;
+	o_tty->count++;
+	return 0;
+
+err_put_module:
+	module_put(driver->other->owner);
+err:
+	kfree(ports[0]);
+	kfree(ports[1]);
+	return retval;
+}
+
+static void pty_cleanup(struct tty_struct *tty)
+{
+	tty_port_put(tty->port);
+}
+
+/* Traditional BSD devices */
+#ifdef CONFIG_LEGACY_PTYS
+
+static int pty_install(struct tty_driver *driver, struct tty_struct *tty)
+{
+	return pty_common_install(driver, tty, true);
+}
+
+static void pty_remove(struct tty_driver *driver, struct tty_struct *tty)
+{
+	struct tty_struct *pair = tty->link;
+
+	driver->ttys[tty->index] = NULL;
+	if (pair)
+		pair->driver->ttys[pair->index] = NULL;
+}
+
+static int pty_bsd_ioctl(struct tty_struct *tty,
+			 unsigned int cmd, unsigned long arg)
+{
+	switch (cmd) {
+	case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
+		return pty_set_lock(tty, (int __user *) arg);
+	case TIOCGPTLCK: /* Get PT Lock status */
+		return pty_get_lock(tty, (int __user *)arg);
+	case TIOCPKT: /* Set PT packet mode */
+		return pty_set_pktmode(tty, (int __user *)arg);
+	case TIOCGPKT: /* Get PT packet mode */
+		return pty_get_pktmode(tty, (int __user *)arg);
+	case TIOCSIG:    /* Send signal to other side of pty */
+		return pty_signal(tty, (int) arg);
+	case TIOCGPTN: /* TTY returns ENOTTY, but glibc expects EINVAL here */
+		return -EINVAL;
+	}
+	return -ENOIOCTLCMD;
+}
+
+#ifdef CONFIG_COMPAT
+static long pty_bsd_compat_ioctl(struct tty_struct *tty,
+				 unsigned int cmd, unsigned long arg)
+{
+	/*
+	 * PTY ioctls don't require any special translation between 32-bit and
+	 * 64-bit userspace, they are already compatible.
+	 */
+	return pty_bsd_ioctl(tty, cmd, (unsigned long)compat_ptr(arg));
+}
+#else
+#define pty_bsd_compat_ioctl NULL
+#endif
+
+static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
+/*
+ * not really modular, but the easiest way to keep compat with existing
+ * bootargs behaviour is to continue using module_param here.
+ */
+module_param(legacy_count, int, 0);
+
+/*
+ * The master side of a pty can do TIOCSPTLCK and thus
+ * has pty_bsd_ioctl.
+ */
+static const struct tty_operations master_pty_ops_bsd = {
+	.install = pty_install,
+	.open = pty_open,
+	.close = pty_close,
+	.write = pty_write,
+	.write_room = pty_write_room,
+	.flush_buffer = pty_flush_buffer,
+	.unthrottle = pty_unthrottle,
+	.ioctl = pty_bsd_ioctl,
+	.compat_ioctl = pty_bsd_compat_ioctl,
+	.cleanup = pty_cleanup,
+	.resize = pty_resize,
+	.remove = pty_remove
+};
+
+static const struct tty_operations slave_pty_ops_bsd = {
+	.install = pty_install,
+	.open = pty_open,
+	.close = pty_close,
+	.write = pty_write,
+	.write_room = pty_write_room,
+	.flush_buffer = pty_flush_buffer,
+	.unthrottle = pty_unthrottle,
+	.set_termios = pty_set_termios,
+	.cleanup = pty_cleanup,
+	.resize = pty_resize,
+	.start = pty_start,
+	.stop = pty_stop,
+	.remove = pty_remove
+};
+
+static void __init legacy_pty_init(void)
+{
+	struct tty_driver *pty_driver, *pty_slave_driver;
+
+	if (legacy_count <= 0)
+		return;
+
+	pty_driver = tty_alloc_driver(legacy_count,
+			TTY_DRIVER_RESET_TERMIOS |
+			TTY_DRIVER_REAL_RAW |
+			TTY_DRIVER_DYNAMIC_ALLOC);
+	if (IS_ERR(pty_driver))
+		panic("Couldn't allocate pty driver");
+
+	pty_slave_driver = tty_alloc_driver(legacy_count,
+			TTY_DRIVER_RESET_TERMIOS |
+			TTY_DRIVER_REAL_RAW |
+			TTY_DRIVER_DYNAMIC_ALLOC);
+	if (IS_ERR(pty_slave_driver))
+		panic("Couldn't allocate pty slave driver");
+
+	pty_driver->driver_name = "pty_master";
+	pty_driver->name = "pty";
+	pty_driver->major = PTY_MASTER_MAJOR;
+	pty_driver->minor_start = 0;
+	pty_driver->type = TTY_DRIVER_TYPE_PTY;
+	pty_driver->subtype = PTY_TYPE_MASTER;
+	pty_driver->init_termios = tty_std_termios;
+	pty_driver->init_termios.c_iflag = 0;
+	pty_driver->init_termios.c_oflag = 0;
+	pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
+	pty_driver->init_termios.c_lflag = 0;
+	pty_driver->init_termios.c_ispeed = 38400;
+	pty_driver->init_termios.c_ospeed = 38400;
+	pty_driver->other = pty_slave_driver;
+	tty_set_operations(pty_driver, &master_pty_ops_bsd);
+
+	pty_slave_driver->driver_name = "pty_slave";
+	pty_slave_driver->name = "ttyp";
+	pty_slave_driver->major = PTY_SLAVE_MAJOR;
+	pty_slave_driver->minor_start = 0;
+	pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
+	pty_slave_driver->subtype = PTY_TYPE_SLAVE;
+	pty_slave_driver->init_termios = tty_std_termios;
+	pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
+	pty_slave_driver->init_termios.c_ispeed = 38400;
+	pty_slave_driver->init_termios.c_ospeed = 38400;
+	pty_slave_driver->other = pty_driver;
+	tty_set_operations(pty_slave_driver, &slave_pty_ops_bsd);
+
+	if (tty_register_driver(pty_driver))
+		panic("Couldn't register pty driver");
+	if (tty_register_driver(pty_slave_driver))
+		panic("Couldn't register pty slave driver");
+}
+#else
+static inline void legacy_pty_init(void) { }
+#endif
+
+/* Unix98 devices */
+#ifdef CONFIG_UNIX98_PTYS
+static struct cdev ptmx_cdev;
+
+/**
+ *	ptm_open_peer - open the peer of a pty
+ *	@master: the open struct file of the ptmx device node
+ *	@tty: the master of the pty being opened
+ *	@flags: the flags for open
+ *
+ *	Provide a race free way for userspace to open the slave end of a pty
+ *	(where they have the master fd and cannot access or trust the mount
+ *	namespace /dev/pts was mounted inside).
+ */
+int ptm_open_peer(struct file *master, struct tty_struct *tty, int flags)
+{
+	int fd;
+	struct file *filp;
+	int retval = -EINVAL;
+	struct path path;
+
+	if (tty->driver != ptm_driver)
+		return -EIO;
+
+	fd = get_unused_fd_flags(flags);
+	if (fd < 0) {
+		retval = fd;
+		goto err;
+	}
+
+	/* Compute the slave's path */
+	path.mnt = devpts_mntget(master, tty->driver_data);
+	if (IS_ERR(path.mnt)) {
+		retval = PTR_ERR(path.mnt);
+		goto err_put;
+	}
+	path.dentry = tty->link->driver_data;
+
+	filp = dentry_open(&path, flags, current_cred());
+	mntput(path.mnt);
+	if (IS_ERR(filp)) {
+		retval = PTR_ERR(filp);
+		goto err_put;
+	}
+
+	fd_install(fd, filp);
+	return fd;
+
+err_put:
+	put_unused_fd(fd);
+err:
+	return retval;
+}
+
+static int pty_unix98_ioctl(struct tty_struct *tty,
+			    unsigned int cmd, unsigned long arg)
+{
+	switch (cmd) {
+	case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
+		return pty_set_lock(tty, (int __user *)arg);
+	case TIOCGPTLCK: /* Get PT Lock status */
+		return pty_get_lock(tty, (int __user *)arg);
+	case TIOCPKT: /* Set PT packet mode */
+		return pty_set_pktmode(tty, (int __user *)arg);
+	case TIOCGPKT: /* Get PT packet mode */
+		return pty_get_pktmode(tty, (int __user *)arg);
+	case TIOCGPTN: /* Get PT Number */
+		return put_user(tty->index, (unsigned int __user *)arg);
+	case TIOCSIG:    /* Send signal to other side of pty */
+		return pty_signal(tty, (int) arg);
+	}
+
+	return -ENOIOCTLCMD;
+}
+
+#ifdef CONFIG_COMPAT
+static long pty_unix98_compat_ioctl(struct tty_struct *tty,
+				 unsigned int cmd, unsigned long arg)
+{
+	/*
+	 * PTY ioctls don't require any special translation between 32-bit and
+	 * 64-bit userspace, they are already compatible.
+	 */
+	return pty_unix98_ioctl(tty, cmd,
+		cmd == TIOCSIG ? arg : (unsigned long)compat_ptr(arg));
+}
+#else
+#define pty_unix98_compat_ioctl NULL
+#endif
+
+/**
+ *	ptm_unix98_lookup	-	find a pty master
+ *	@driver: ptm driver
+ *	@file: unused
+ *	@idx: tty index
+ *
+ *	Look up a pty master device. Called under the tty_mutex for now.
+ *	This provides our locking.
+ */
+
+static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver,
+		struct file *file, int idx)
+{
+	/* Master must be open via /dev/ptmx */
+	return ERR_PTR(-EIO);
+}
+
+/**
+ *	pts_unix98_lookup	-	find a pty slave
+ *	@driver: pts driver
+ *	@file: file pointer to tty
+ *	@idx: tty index
+ *
+ *	Look up a pty master device. Called under the tty_mutex for now.
+ *	This provides our locking for the tty pointer.
+ */
+
+static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver,
+		struct file *file, int idx)
+{
+	struct tty_struct *tty;
+
+	mutex_lock(&devpts_mutex);
+	tty = devpts_get_priv(file->f_path.dentry);
+	mutex_unlock(&devpts_mutex);
+	/* Master must be open before slave */
+	if (!tty)
+		return ERR_PTR(-EIO);
+	return tty;
+}
+
+static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty)
+{
+	return pty_common_install(driver, tty, false);
+}
+
+/* this is called once with whichever end is closed last */
+static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
+{
+	struct pts_fs_info *fsi;
+
+	if (tty->driver->subtype == PTY_TYPE_MASTER)
+		fsi = tty->driver_data;
+	else
+		fsi = tty->link->driver_data;
+
+	if (fsi) {
+		devpts_kill_index(fsi, tty->index);
+		devpts_release(fsi);
+	}
+}
+
+static void pty_show_fdinfo(struct tty_struct *tty, struct seq_file *m)
+{
+	seq_printf(m, "tty-index:\t%d\n", tty->index);
+}
+
+static const struct tty_operations ptm_unix98_ops = {
+	.lookup = ptm_unix98_lookup,
+	.install = pty_unix98_install,
+	.remove = pty_unix98_remove,
+	.open = pty_open,
+	.close = pty_close,
+	.write = pty_write,
+	.write_room = pty_write_room,
+	.flush_buffer = pty_flush_buffer,
+	.unthrottle = pty_unthrottle,
+	.ioctl = pty_unix98_ioctl,
+	.compat_ioctl = pty_unix98_compat_ioctl,
+	.resize = pty_resize,
+	.cleanup = pty_cleanup,
+	.show_fdinfo = pty_show_fdinfo,
+};
+
+static const struct tty_operations pty_unix98_ops = {
+	.lookup = pts_unix98_lookup,
+	.install = pty_unix98_install,
+	.remove = pty_unix98_remove,
+	.open = pty_open,
+	.close = pty_close,
+	.write = pty_write,
+	.write_room = pty_write_room,
+	.flush_buffer = pty_flush_buffer,
+	.unthrottle = pty_unthrottle,
+	.set_termios = pty_set_termios,
+	.start = pty_start,
+	.stop = pty_stop,
+	.cleanup = pty_cleanup,
+};
+
+/**
+ *	ptmx_open		-	open a unix 98 pty master
+ *	@inode: inode of device file
+ *	@filp: file pointer to tty
+ *
+ *	Allocate a unix98 pty master device from the ptmx driver.
+ *
+ *	Locking: tty_mutex protects the init_dev work. tty->count should
+ *		protect the rest.
+ *		allocated_ptys_lock handles the list of free pty numbers
+ */
+
+static int ptmx_open(struct inode *inode, struct file *filp)
+{
+	struct pts_fs_info *fsi;
+	struct tty_struct *tty;
+	struct dentry *dentry;
+	int retval;
+	int index;
+
+	nonseekable_open(inode, filp);
+
+	/* We refuse fsnotify events on ptmx, since it's a shared resource */
+	filp->f_mode |= FMODE_NONOTIFY;
+
+	retval = tty_alloc_file(filp);
+	if (retval)
+		return retval;
+
+	fsi = devpts_acquire(filp);
+	if (IS_ERR(fsi)) {
+		retval = PTR_ERR(fsi);
+		goto out_free_file;
+	}
+
+	/* find a device that is not in use. */
+	mutex_lock(&devpts_mutex);
+	index = devpts_new_index(fsi);
+	mutex_unlock(&devpts_mutex);
+
+	retval = index;
+	if (index < 0)
+		goto out_put_fsi;
+
+
+	mutex_lock(&tty_mutex);
+	tty = tty_init_dev(ptm_driver, index);
+	/* The tty returned here is locked so we can safely
+	   drop the mutex */
+	mutex_unlock(&tty_mutex);
+
+	retval = PTR_ERR(tty);
+	if (IS_ERR(tty))
+		goto out;
+
+	/*
+	 * From here on out, the tty is "live", and the index and
+	 * fsi will be killed/put by the tty_release()
+	 */
+	set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
+	tty->driver_data = fsi;
+
+	tty_add_file(tty, filp);
+
+	dentry = devpts_pty_new(fsi, index, tty->link);
+	if (IS_ERR(dentry)) {
+		retval = PTR_ERR(dentry);
+		goto err_release;
+	}
+	tty->link->driver_data = dentry;
+
+	retval = ptm_driver->ops->open(tty, filp);
+	if (retval)
+		goto err_release;
+
+	tty_debug_hangup(tty, "opening (count=%d)\n", tty->count);
+
+	tty_unlock(tty);
+	return 0;
+err_release:
+	tty_unlock(tty);
+	// This will also put-ref the fsi
+	tty_release(inode, filp);
+	return retval;
+out:
+	devpts_kill_index(fsi, index);
+out_put_fsi:
+	devpts_release(fsi);
+out_free_file:
+	tty_free_file(filp);
+	return retval;
+}
+
+static struct file_operations ptmx_fops __ro_after_init;
+
+static void __init unix98_pty_init(void)
+{
+	ptm_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
+			TTY_DRIVER_RESET_TERMIOS |
+			TTY_DRIVER_REAL_RAW |
+			TTY_DRIVER_DYNAMIC_DEV |
+			TTY_DRIVER_DEVPTS_MEM |
+			TTY_DRIVER_DYNAMIC_ALLOC);
+	if (IS_ERR(ptm_driver))
+		panic("Couldn't allocate Unix98 ptm driver");
+	pts_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
+			TTY_DRIVER_RESET_TERMIOS |
+			TTY_DRIVER_REAL_RAW |
+			TTY_DRIVER_DYNAMIC_DEV |
+			TTY_DRIVER_DEVPTS_MEM |
+			TTY_DRIVER_DYNAMIC_ALLOC);
+	if (IS_ERR(pts_driver))
+		panic("Couldn't allocate Unix98 pts driver");
+
+	ptm_driver->driver_name = "pty_master";
+	ptm_driver->name = "ptm";
+	ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
+	ptm_driver->minor_start = 0;
+	ptm_driver->type = TTY_DRIVER_TYPE_PTY;
+	ptm_driver->subtype = PTY_TYPE_MASTER;
+	ptm_driver->init_termios = tty_std_termios;
+	ptm_driver->init_termios.c_iflag = 0;
+	ptm_driver->init_termios.c_oflag = 0;
+	ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
+	ptm_driver->init_termios.c_lflag = 0;
+	ptm_driver->init_termios.c_ispeed = 38400;
+	ptm_driver->init_termios.c_ospeed = 38400;
+	ptm_driver->other = pts_driver;
+	tty_set_operations(ptm_driver, &ptm_unix98_ops);
+
+	pts_driver->driver_name = "pty_slave";
+	pts_driver->name = "pts";
+	pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
+	pts_driver->minor_start = 0;
+	pts_driver->type = TTY_DRIVER_TYPE_PTY;
+	pts_driver->subtype = PTY_TYPE_SLAVE;
+	pts_driver->init_termios = tty_std_termios;
+	pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
+	pts_driver->init_termios.c_ispeed = 38400;
+	pts_driver->init_termios.c_ospeed = 38400;
+	pts_driver->other = ptm_driver;
+	tty_set_operations(pts_driver, &pty_unix98_ops);
+
+	if (tty_register_driver(ptm_driver))
+		panic("Couldn't register Unix98 ptm driver");
+	if (tty_register_driver(pts_driver))
+		panic("Couldn't register Unix98 pts driver");
+
+	/* Now create the /dev/ptmx special device */
+	tty_default_fops(&ptmx_fops);
+	ptmx_fops.open = ptmx_open;
+
+	cdev_init(&ptmx_cdev, &ptmx_fops);
+	if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
+	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
+		panic("Couldn't register /dev/ptmx driver");
+	device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, "ptmx");
+}
+
+#else
+static inline void unix98_pty_init(void) { }
+#endif
+
+static int __init pty_init(void)
+{
+	legacy_pty_init();
+	unix98_pty_init();
+	return 0;
+}
+device_initcall(pty_init);