While testing 32bit UEFI OVMF (which has bug about how the disk size
is presented), I did witness the errors from blkio->ReadBlocks().
It became apparent we can not entirely trust UEFI interfaces either,
so additional checks are needed.
So we use disk_ioctl(DIOCGMEDIASIZE) for disks, with fallback of
Media->LastBlock for other media.
In addition, we need to check if there is media present.
+ small fixes for error printout, and avoiding multiple blk * 512.