[Qemu-devel] How to get beyond the 16 head limit?

[Erik Mouw]

Hi,

We managed to recover data from an ancient 60 MB ESDI drive. Because
the interesting data is in some kind of proprietary database system
(running on top of its own OS) I tried to run the recovered disk image
in Qemu and let the database export itself to a floppy image.

The drive has an unusual though valid geometry: 58 cylinders, 64 heads,
32 sectors. Qemu refuses to boot the image because it says the CHS
format is invalid:

address@hidden:~/qemu > qemu -fda scratch.img -hda bd4467.img \
      -hdachs 58,64,32 -std-vga -boot c -m 4 -net none
qemu: invalid physical CHS format

I increased the head limit in vl.c from 16 to 64 but it appears that is
not enough to convince Qemu to accept the geometry. Qemu starts, but
when I check from DOS (in Qemu) it now looks as if the drive geometry
is 116/16/63. With a partition table patched to match that geometry I
can boot the database OS bootsector, which happily loads the db OS
kernel from the wrong location because it uses CHS addressing (instead
of LBA). Needles to say that won't fly.

Like I said, I already increased the head limit in vl.c but that is
apparently not enough. What else do I have to change to get Qemu to use
my supplied disk geometry?


Regards,

Erik

PS: I am using qemu-0.9.1 for this experiment

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