blkdev_get_by_path — open a block device by name
| struct block_device * blkdev_get_by_path ( | const char * path, | 
| fmode_t mode, | |
| void * holder ); | 
   Open the blockdevice described by the device file at path.  mode
   and holder are identical to blkdev_get.
   
On success, the returned block_device has reference count of one.