SEEK_HOLE or FIEMAP?

<rant>
> It's much cleaner to have the boot loader use the proper directories, block maps, etc. to
access the filesystem. GRUB does this.

 So does Gujin - smaller number of filesystem supported, I have to say.

> In its usual deployment, GRUB still has the problem because that code that knows how to
access the filesystem is in the filesystem, and the only way GRUB knows to find it is with
built-in block numbers.

 So does Gujin.

> But it's possible to put that code outside the filesystem, in an area of disk reserved for
that purpose, and then the world is as it should be.

 By default Gujin puts that code at the end of the disk, outside of any filesystem, but it not
always available depending on the tool used to create the partitions (Linux tools are used to
fill the whole disk - not leaving a single unallocated sector for the bootloader).
</rant>

 Doesn't change that it would be nice to have a kernel interface which maps the device block
into a hard disk block, for that part of the bootloader which shall not move when it is on a
filesystem (RAID and LVM problem).
 It would also be nice to have an interface to tell the filesystem that this file is the boot
code - there is an inode reserved for that in EXT2/3FS but no way to use it.