Not many people have seen this, but the i_bdev field in fake_inode in 
ioctl_by_bdev() is uninitialised.  Since this field is dereferenced by 
BLKFLSBUF in rd_ioctl, it can lead to a panic (depending on what happens to be 
on the stack).  The attached fixes the problem and clears all the fields in 
fake_inode to make any other problems like this show up.

James Bottomley