error in char device module compilation

**pawan_dear** · September 16th, 2011

i am getting the following error------------------------------------------

/home/kk/module_programming/fileops.c:30: warning: initialization from incompatible pointer type
/home/kk/module_programming/fileops.c: In function ‘cleanup_module’:
/home/kk/module_programming/fileops.c:57: error: void value not ignored as it ought to be
/home/kk/module_programming/fileops.c: At top level:
/home/kk/module_programming/fileops.c:81: error: conflicting types for ‘device_release’
/home/kk/module_programming/fileops.c:10: note: previous declaration of ‘device_release’ was here
/home/kk/module_programming/fileops.c: In function ‘__inittest’:
/home/kk/module_programming/fileops.c:112: error: ‘start’ undeclared (first use in this function)
/home/kk/module_programming/fileops.c:112: error: (Each undeclared identifier is reported only once
/home/kk/module_programming/fileops.c:112: error: for each function it appears in.)
/home/kk/module_programming/fileops.c: At top level:
/home/kk/module_programming/fileops.c:112: error: redefinition of ‘init_module’
/home/kk/module_programming/fileops.c:32: note: previous definition of ‘init_module’ was here
/home/kk/module_programming/fileops.c: In function ‘__exittest’:
/home/kk/module_programming/fileops.c:113: error: ‘stop’ undeclared (first use in this function)
/home/kk/module_programming/fileops.c: At top level:
/home/kk/module_programming/fileops.c:113: error: redefinition of ‘cleanup_module’
/home/kk/module_programming/fileops.c:55: note: previous definition of ‘cleanup_module’ was here
/home/kk/module_programming/fileops.c:114: error: expected declaration specifiers or ‘...’ before string constant
/home/kk/module_programming/fileops.c:114: warning: data definition has no type or storage class
/home/kk/module_programming/fileops.c:114: warning: type defaults to ‘int’ in declaration of ‘MODULE_LICENCE’
/home/kk/module_programming/fileops.c:114: warning: function declaration isn’t a prototype
make[2]: *** [/home/kk/module_programming/fileops.o] Error 1
make[1]: *** [_module_/home/kk/module_programming] Error 2
make[1]: Leaving directory `/usr/src/kernels/2.6.32-71.el6.x86_64'
make: *** [modules] Error 2

my programe code

#include<linux/kernel.h>
#include<linux/module.h>
#include<linux/fs.h>
#include<asm/uaccess.h>

int init_module(void);
void cleanup_module(void);

static int device_open(struct inode *, struct file *);
static int device_release(struct file *, struct file *);

static ssize_t device_read(struct file *, char *, size_t, loff_t *);
static ssize_t device_write(struct file *, const char *, size_t, loff_t *);

#define SUCCESS 0
#define DEVICE_NAME "chardev"
#define BUF_LEN 80

static int Major;
static int Device_Open = 0;

static char msg[BUF_LEN];
static char *msg_Ptr;

static struct file_operations fops = {
.read = device_read,
.write = device_write,
.open = device_open,
.release=device_release
};

int init_module(void)
{
Major = register_chrdev( 0, DEVICE_NAME, &fops);

if ( Major < 0 )
{
printk("Registering char device failed with %d\n", Major);
return Major;
}

printk("I was assinged major number %d. to talk \n",Major);
printk("the driver create a dev file with \n");
printk("mknod /dev/%s c %d 0 .\n", DEVICE_NAME, Major);

return SUCCESS;
}

void cleanup_module(void)
{
int ret = unregister_chrdev ( Major, DEVICE_NAME );

if( ret < 0 )
printk("Error in unregister_chardev : %d \n",ret);

}

static int device_open(struct inode *inode, struct file *file)
{
static int counter = 0;

if( Device_Open)
return -EBUSY;

Device_Open++;
sprintf(msg, "I already told you %d times Hello World \n", counter++);

msg_Ptr = msg ;
try_module_get(THIS_MODULE);

return SUCCESS;
}

static int device_release( struct inode *inode, struct file *file)
{
Device_Open--;

module_put (THIS_MODULE);
return 0;
}

static ssize_t device_read( struct file *file, char *buffer, size_t length, loff_t *offset )
{
int bytes_read = 0;

if( *msg_Ptr == 0)
return 0;

while( length && *msg_Ptr )
{
put_user( *(msg_Ptr++), buffer++ );
length--;
bytes_read++;
}

return bytes_read;
}

static ssize_t device_write( struct file *filp, const char *buff, size_t len, loff_t *off )
{
printk("sorry, this operation isn';t supported. \n");
return -EINVAL;
}

module_init(start);
module_exit(stop);
MODULE_LICENCE("GPL");

**SevenMachines** · September 21st, 2011

You have

Code:

static int device_release(struct file *, struct file *);

which I'm guessing you meant

Code:

static int device_release(struct inode *, struct file *);

unregister_chrdev returns void in newer kernels so dont use the return value, change

Code:

int ret    = unregister_chrdev ( Major, DEVICE_NAME );
    
    if( ret < 0 )
        printk("Error in unregister_chardev : %d \n",ret);

to simply

Code:

unregister_chrdev ( Major, DEVICE_NAME );

You're using

Code:

module_init(start);
module_exit(stop);

to direct the kernel to two non-existent load and unload functions, you could implement them of course but you're using init_module and cleanup_module anyway so just remove those module_init/_exit calls

You have

Code: