Linux操作系统内核和设备文件对话(1)(3)

/* 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 were 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 wouldnt

* 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. */

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

static ssize_t device_write(struct file *file,

const char *buffer,

size_t length,

loff_t *offset)

#else

static int device_write(struct inode *inode,

struct file *file,

const char *buffer,

int length)

#endif

{

int i;

#ifdef DEBUG

printk ("device_write(%p,%s,%d)",

file, buffer, length);

#endif

for(i=0; i

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

get_user(Message, buffer+i);

#else

Message = get_user(buffer+i);

#endif

Message_Ptr = Message;

/* Again, return the number of input characters used */

return i;

}

/* This function is called whenever a process tries to

* do an ioctl on our device file. We get two extra

* parameters (additional to the inode and file

* structures, which all device functions get): the number

* of the ioctl called and the parameter given to the

* ioctl function.

*

* If the ioctl is write or read/write (meaning output

* is returned to the calling process), the ioctl call

* returns the output of this function.

*/

int device_ioctl(

struct inode *inode,

struct file *file,

unsigned int ioctl_num,/* The number of the ioctl */

unsigned long ioctl_param) /* The parameter to it */