Энциклопедия разработчика модулей ядра Linux - [10]
Ioctl номер кодирует главный номер устройства, тип ioctl команды и тип параметра. Этот ioctl номер обычно создается макрообращением (_IO, _IOR, _IOW или _IOWR: в зависимости от типа) в файле заголовка. Этот файл заголовка должен быть присоединен командой #include программой, которая использует ioctl и модулем (так что они могут генерировать соответствующие ioctl). В примере ниже, файл заголовка chardev.h и программа, которая использует это ioctl.c.
Если Вы хотите использовать ioctl в ваших собственных модулях, самое лучшее получить официальное ioctl назначение, так, если Вы случайно получаете ioctl кого-то другого вы будете знать, что что-то неправильно. Для большего количества информации, проконсультируйтесь в файле `Documentation/ioctl-number.txt' дерева исходников ядра.
>/* chardev.c
>*
>* Create an input/output character device
>*/
>/* Copyright (C) 1998-99 by Ori Pomerantz */
>/* The necessary header files */
>/* Standard in kernel modules */
>#include
>#include
>/* Deal with CONFIG_MODVERSIONS */
>#if CONFIG_MODVERSIONS==1
>#define MODVERSIONS
>#include
>#endif
>/* For character devices */
>/* The character device definitions are here */
>#include
>/* A wrapper which does next to nothing at
>* at present, but may help for compatibility
>* with future versions of Linux */
>#include
>/* Our own ioctl numbers */
>#include "chardev.h"
>/* In 2.2.3 /usr/include/linux/version.h includes a
>* macro for this, but 2.0.35 doesn't - so I add it
>* here if necessary. */
>#ifndef KERNEL_VERSION
>#define KERNEL_VERSION(a,b,c) ((a)*65536+(b)*256+(c))
>#endif
>#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
>#include
>#endif
>#define SUCCESS 0
>/* Device Declarations ******************************** */
>/* The name for our device, as it will appear in /proc/devices */
>#define DEVICE_NAME "char_dev"
>/* The maximum length of the message for the device */
>#define BUF_LEN 80
>/* Is the device open right now? Used to prevent concurent access into the same device */
>static int Device_Open = 0;
>/* The message the device will give when asked */
>static char Message[BUF_LEN];
>/* How far did the process reading the message get?
>* Useful if the message is larger than the size of the
>* buffer we get to fill in device_read. */
>static char *Message_Ptr;
>/* This function is called whenever a process attempts to open the device file */
>static int device_open(struct inode *inode, struct file *file) {
>#ifdef DEBUG
> printk("device_open(%p)\n", file);
>#endif
> /* We don't want to talk to two processes at the same time */
> if (Device_Open) return -EBUSY;
> /* If this was a process, we would have had to be
> * more careful here, because one process might have
> * checked Device_Open right before the other one
> * tried to increment it. However, we're in the
> * kernel, so we're protected against context switches.
> *
> * This is NOT the right attitude to take, because we
> * might be running on an SMP box, but we'll deal with
> * SMP in a later chapter. */
> Device_Open++;
> /* Initialize the message */
> Message_Ptr = Message;
> MOD_INC_USE_COUNT;
> return SUCCESS;
>}
>/* This function is called when a process closes the
>* device file. It doesn't have a return value because
>* it cannot fail. Regardless of what else happens, you
>* should always be able to close a device (in 2.0, a 2.2
>* device file could be impossible to close). */
>#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
>static int device_release(struct inode *inode, struct file *file)
>#else
>static void device_release(struct inode *inode, struct file *file)
>#endif
>{
>#ifdef DEBUG
> printk("device_release(%p,%p)\n", inode, file);
>#endif
> /* We're now ready for our next caller */
> Device_Open--;
> MOD_DEC_USE_COUNT;
>#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
> return 0;
>#endif
>}
>/* This function is called whenever a process which
>* has already opened the device file attempts to read from it. */
>#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
>static ssize_t device_read(
> struct file *file,
> char *buffer, /* The buffer to fill with the data */
> size_t length, /* The length of the buffer */
> loff_t *offset) /* offset to the file */
>#else
>static int device_read(
> struct inode *inode, struct file *file,
> char *buffer, /* The buffer to fill with the data */
> int length) /* The length of the buffer (mustn't write beyond that!) */
>#endif
>{
> /* Number of bytes actually written to the buffer */
> int bytes_read = 0;
>#ifdef DEBUG
> printk("device_read(%p,%p,%d)\n", file, buffer, length);
>#endif
> /* If we're at the end of the message, return 0 (which signifies end of file) */
> if (*Message_Ptr == 0) return 0;
> /* Actually put the data into the buffer */
