Энциклопедия разработчика модулей ядра Linux
Шрифт:
return 0;
#endif
}
/* This function is called whenever a process which
* have 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 data */
size_t length, /* The length of the buffer */
loff_t *offset) /* Our offset in 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;
/* 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 */
while (length && *Message_Ptr) {
/* Because the buffer is in the user data segment,
* not the kernel data segment, assignment wouldn't
* work. Instead, we have to use put_user which
* copies data from the kernel data segment to the
* user data segment. */
put_user(*(Message_Ptr++), buffer++);
length--;
bytes_read++;
}
#ifdef DEBUG
printk("Read %d bytes, %d left\n", bytes_read, length);
#endif
/* Read functions are supposed to return the number of bytes actually inserted into the buffer */
return bytes_read;
}
/* This function is called when somebody tries to write
* into our device file - unsupported in this example. */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
static ssize_t device_write(struct file *file,
const char *buffer, /* The buffer */
size_t length, /* The length of the buffer */
loff_t *offset) /* Our offset in the file */
#else
static int device_write(struct inode *inode, struct file *file, const char *buffer, int length)
#endif
{
return -EINVAL;
}
/* Module Declarations ***************************** */
/* The major device number for the device. This is
* global (well, static, which in this context is global
* within this file) because it has to be accessible * both for registration and for release. */
static int Major;
/* This structure will hold the functions to be
* called when a process does something to the device
* we created. Since a pointer to this structure is
* kept in the devices table, it can't be local to
* init_module. NULL is for unimplemented functions. */
struct file_operations Fops = {
NULL, /* seek */
device_read, device_write,
NULL, /* readdir */
NULL, /* select */
NULL, /* ioctl */
NULL, /* mmap */
device_open,
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
NULL, /* flush */
#endif
device_release /* a.k.a. close */
};
/* Initialize the module - Register the character device */
int init_module {
/* Register the character device (atleast try) */
Major = module_register_chrdev(0, DEVICE_NAME, &Fops);
/* Negative values signify an error */
if (Major < 0) {
printk("%s device failed with %d\n", "Sorry, registering the character", Major);
return Major;
}
printk("%s The major device number is %d.\n", "Registeration is a success.", Major);
printk("If you want to talk to the device driver,\n");
printk("you'll have to create a device file. \n");
printk("We suggest you use:\n");
printk("mknod <name> c %d <minor>\n", Major);
printk("You can try different minor numbers %s", "and see what happens.\n");
return 0;
}
/* Cleanup - unregister the appropriate file from /proc */
void cleanup_module {
int ret;
/* Unregister the device */
ret = module_unregister_chrdev(Major, DEVICE_NAME);
/* If there's an error, report it */
if (ret < 0) printk("Error in unregister_chrdev: %d\n", ret);
}
Исходники
Системные вызовы, которые являются главным интерфейсом ядра, для процессов выглядят одинаково, независимо от версии. Новый системный вызов может быть добавлен, но старые обычно будут вести себя точно так, как и раньше. Это необходимо для обратной совместимости новая версия ядра, как предполагается, не разрывает регулярные процессы. В большинстве случаев, файлы устройства также останутся теми же самыми. С другой стороны, внутренние интерфейсы ядра могут изменяться между версиями.
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