bmap - find a block number in a file
sector_t bmap (struct inode * inode, sector_t block);
inode inode of file block block to find
Returns the block number on the device holding the inode that is the disk block number for the block of the file requested. That is, asked for block 4 of inode 1 the function will return the disk block relative to the disk start that holds that block of the file.