We have created a block driver which traces the IO operations happening on a particular block device say /dev/sdb or /dev/sdc.
It's working, so now I am trying to develop a user space application that will interact with driver (add or remove block device from userspace).
I have created a skeleton and underlying program but facing an error 'invalid argument'.

My userspace program is like this:

char path[SIZE];
printf( "Enter the path of the block device to add or remove: ");
fgets(path, SIZE, stdin);
path[strcspn(path, "\n")] = '\0';

int fd = open( path, O_RDWR );

if( fd < 0 )
{
perror( "Failed to open device" );
exit( EXIT_FAILURE );
}

while( 1 )
{
int input;

printf( "Enter a number [ 0 for add and 1 for remove ]: " );
scanf( "%d", &input );

switch( input )
{
case 0:
if( ioctl( fd, MY_BLOCK_DEVICE_ADD, &path ) < 0 )
{
perror( "Failed to add device" );
exit( EXIT_FAILURE );
}
break;

case 1:
if( ioctl( fd, MY_BLOCK_DEVICE_REMOVE, &path ) < 0 )
{
perror( "Failed to remove device" );
exit( EXIT_FAILURE );
}

break;

case 2:
close(fd);
return 0;
}
}

in '.h' file I have defined custom IOCTL commands -

#define MY_BLOCK_DEVICE_ADD _IOWR('M', 1, char*)
#define MY_BLOCK_DEVICE_REMOVE _IOWR('M', 2, char*)

in driver/module code -

static int device_ioctl( struct block_device *dev, fmode_t mode, unsigned int cmd, unsigned long arg )
{
printk(KERN_INFO "in ioctl\n");
int ret;
char path[SIZE];
switch( cmd )
{
case MY_BLOCK_DEVICE_ADD:
if( copy_from_user( path, (char *)arg, SIZE ) )
{
return -EFAULT;
}

path[strcspn(path, "\n")] = '\0';

register_block_device(path);

printk( KERN_INFO "Device added\n" );
break;

case MY_BLOCK_DEVICE_REMOVE:
if( copy_from_user( path, (char *)arg, SIZE ) )
{
return -EFAULT;
}

unregister_block_device();
printk( KERN_INFO "Device removed\n" );
break;

default:
return -ENOTTY;
}
return 0;
}

Proposed working - We pass IOCTL commands from userspace add/remove device. So, for add ioctl device will be registered with my block driver which will start tracking the changes for ex. /dev/sdb and remove will stop the tracking.
So, do you know how can I solve this error? or if there is better approach plz feel free to give your valuable suggestions.

It would help if you edited your question and used code tags so it is properly formatted and readable. What code is giving the 'Invalid argument' error?

Thanks @smallpond. I have edited my question, now code is in red color lines.
And my userspace program is giving 'invalid argument' error.

If you enter "/dev/sdb", you are opening "/dev/sdb" and sending it an ioctl request that it does not understand. It returns EINVAL, because it has no idea what MY_BLOCK_DEVICE_* means. You must pass the path and the request to your own driver, not to /dev/sdb.

1 members found this post helpful.

Thanks, you were right. I corrected my code and now it is working.