Энциклопедия разработчика модулей ядра Linux

static struct wait_queue *WaitQ = NULL;

/* Called when the /proc file is opened */

static int module_open(struct inode *inode, struct file *file) {

 /* If the file's flags include O_NONBLOCK, it means

 * the process doesn't want to wait for the file.

 * In this case, if the file is already open, we

 * should fail with -EAGAIN, meaning "you'll have to

 * try again", instead of blocking a process which

 * would rather stay awake. */

 if ((file->f_flags & O_NONBLOCK) && Already_Open) return -EAGAIN;

 /* This is the correct place for MOD_INC_USE_COUNT

 * because if a process is in the loop, which is

 * within the kernel module, the kernel module must

 * not be removed. */

 MOD_INC_USE_COUNT;

 /* If the file is already open, wait until it isn't */

 while (Already_Open) {

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)

  int i, is_sig=0;

#endif

  /* This function puts the current process,

  * including any system calls, such as us, to sleep.

  * Execution will be resumed right after the function

  * call, either because somebody called

  * wake_up(&WaitQ) (only module_close does that,

  * when the file is closed) or when a signal, such

  * as Ctrl-C, is sent to the process */

  module_interruptible_sleep_on(&WaitQ);

  /* If we woke up because we got a signal we're not

  * blocking, return -EINTR (fail the system call).

  * This allows processes to be killed or stopped. */

  /*

  * Emmanuel Papirakis:

  *

  * This is a little update to work with 2.2.*. Signals

  * now are contained in two words (64 bits) and are

  * stored in a structure that contains an array of two

  * unsigned longs. We now have to make 2 checks in our if.

  *

  * Ori Pomerantz:

  *

  * Nobody promised me they'll never use more than 64

  * bits, or that this book won't be used for a version

  * of Linux with a word size of 16 bits. This code

  * would work in any case. */

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)

  for(i=0; i<_NSIG_WORDS && !is_sig; i++) is_sig = current->signal.sig[i] & current->blocked.sig[i];

  if (is_sig) {

#else

  if (current->signal & current->blocked) {

#endif

   /* It's important to put MOD_DEC_USE_COUNT here,

   * because for processes where the open is

   * interrupted there will never be a corresponding

   * close. If we don't decrement the usage count

   * here, we will be left with a positive usage

   * count which we'll have no way to bring down to

   * zero, giving us an immortal module, which can

   * only be killed by rebooting the machine. */

   MOD_DEC_USE_COUNT;

   return -EINTR;

  }

 }

 /* If we got here, Already_Open must be zero */

 /* Open the file */

 Already_Open = 1;

 return 0;  /* Allow the access */

}