tty_mutex.c

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#include <linux/tty.h>
#include <linux/module.h>
#include <linux/kallsyms.h>
#include <linux/semaphore.h>
#include <linux/sched.h>

/* Legacy tty mutex glue */

enum {
    TTY_MUTEX_NORMAL,
    TTY_MUTEX_NESTED,
};

/*
 * Getting the big tty mutex.
 */

static void __lockfunc tty_lock_nested(struct tty_struct *tty,
                       unsigned int subclass)
{
    if (tty->magic != TTY_MAGIC) {
        printk(KERN_ERR "L Bad %p\n", tty);
        WARN_ON(1);
        return;
    }
    tty_kref_get(tty);
    mutex_lock_nested(&tty->legacy_mutex, subclass);
}

void __lockfunc tty_lock(struct tty_struct *tty)
{
    return tty_lock_nested(tty, TTY_MUTEX_NORMAL);
}
EXPORT_SYMBOL(tty_lock);

void __lockfunc tty_unlock(struct tty_struct *tty)
{
    if (tty->magic != TTY_MAGIC) {
        printk(KERN_ERR "U Bad %p\n", tty);
        WARN_ON(1);
        return;
    }
    mutex_unlock(&tty->legacy_mutex);
    tty_kref_put(tty);
}
EXPORT_SYMBOL(tty_unlock);

/*
 * Getting the big tty mutex for a pair of ttys with lock ordering
 * On a non pty/tty pair tty2 can be NULL which is just fine.
 */
void __lockfunc tty_lock_pair(struct tty_struct *tty,
                    struct tty_struct *tty2)
{
    if (tty < tty2) {
        tty_lock(tty);
        tty_lock_nested(tty2, TTY_MUTEX_NESTED);
    } else {
        if (tty2 && tty2 != tty)
            tty_lock(tty2);
        tty_lock_nested(tty, TTY_MUTEX_NESTED);
    }
}
EXPORT_SYMBOL(tty_lock_pair);

void __lockfunc tty_unlock_pair(struct tty_struct *tty,
                        struct tty_struct *tty2)
{
    tty_unlock(tty);
    if (tty2 && tty2 != tty)
        tty_unlock(tty2);
}
EXPORT_SYMBOL(tty_unlock_pair);