[syslinux] BIOS disk geometry and Linux 2.6

[H. Peter Anvin]

> 
> Also, I need to solve the BIOS/Linux disk mapping problem anyway, so
> it does not help to kill two birds with one stone here.  (Even if the
> disk encodes its own geometry in the partition table, I still have to
> figure out that the boot disk is "/dev/hda" before I can partition
> it.)
> 


> On the bright side, it looks like COM32 provides a fantastic interface
> for this.  And the samples are great.
> 
> A better solution, as Michael points out, is probably for setup.S to
> do this work and make the results visible via /sys.  But the COM32
> interface is so nice...
> 
> I am envisioning a COM32 program which passes a kernel parameter like
> so:
> 
>     legacy_chs=1033/255/63,2048/240/63,...
> 
> Where the comma-separated fields are C/H/S values for drive 80h, 81h,
> and so on.

The problem, again, is that there is no way (w/o EDD3) to map these to 
Linux devices.  Linux can get this data on its own (using setup.S or 
whatnot); the problem is that it doesn't know /dev/sda maps to 0x82, for 
example.

Now, from the looks of it, you actually have a system which does support 
EDD3, and it gives the wrong answers.  That would be a serious bug, and 
an indication that the EDD3 code needs to be extended to collect more data.

	-hpa