release/src-rt-6.x.4708/linux/linux-2.6.36/drivers/char/tty_mutex.c

   1 /*
   2  * drivers/char/tty_lock.c
   3  */
   4 #include <linux/tty.h>
   5 #include <linux/module.h>
   6 #include <linux/kallsyms.h>
   7 #include <linux/semaphore.h>
   8 #include <linux/sched.h>
   9
  10 /*
  11  * The 'big tty mutex'
  12  *
  13  * This mutex is taken and released by tty_lock() and tty_unlock(),
  14  * replacing the older big kernel lock.
  15  * It can no longer be taken recursively, and does not get
  16  * released implicitly while sleeping.
  17  *
  18  * Don't use in new code.
  19  */
  20 static DEFINE_MUTEX(big_tty_mutex);
  21 struct task_struct *__big_tty_mutex_owner;
  22 EXPORT_SYMBOL_GPL(__big_tty_mutex_owner);
  23
  24 /*
  25  * Getting the big tty mutex.
  26  */
  27 void __lockfunc tty_lock(void)
  28 {
  29         struct task_struct *task = current;
  30
  31         WARN_ON(__big_tty_mutex_owner == task);
  32
  33         mutex_lock(&big_tty_mutex);
  34         __big_tty_mutex_owner = task;
  35 }
  36 EXPORT_SYMBOL(tty_lock);
  37
  38 void __lockfunc tty_unlock(void)
  39 {
  40         struct task_struct *task = current;
  41
  42         WARN_ON(__big_tty_mutex_owner != task);
  43         __big_tty_mutex_owner = NULL;
  44
  45         mutex_unlock(&big_tty_mutex);
  46 }
  47 EXPORT_SYMBOL(tty_unlock);