path: root/drivers/tty/tty_ldisc.c

#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/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