Re: bootxx needs to fit within 0th track of MBR partition?

Martin Husemann <[email protected]> writes:

>> But, I've never found the original resource which says
>> "second stage loaders in MBR partitions ought/need to
>> fit within 0th track".
>
> I think this used to be a limitation of the boot code inside the MBR.
> The BIOS really only loads the the MBR, everything else is done by the
> code in there and other code it loads and chains to.

This makes sense to me.

I would expect the real issue is that we have a layout

  mbr
  disklabel
  bootxx start
  ...
  bootxx end
  [maybe some unused]
  beginning of UFS

and I dimly remember 16 sectors, but looking at a UFS2 it seems to start
128 sectors in.  The same for UFS1, but that system has boot blocks so
the zero pattern is slightly less clear.    I am probably remembering
6th or 7th edition.

I don't see that we need to cross the bridge of pulling out floppy
support (I probably have working drives) to allow moving from 13 to 18.

It looks like we can go to 126 before it doesn't fit inside UFS2.

Probably installboot should enforce not crossing into a fs and probably
it does.