[dm-devel] HDIO_GETGEO doesn't work on dm devices...

[Darrick J. Wong]

Hi there,

I've been trying to install grub on a "bootable" device-mapper array
that was created with dmraid.  (I've a fakeraid card that will set up
the requisite BIOS drive fiction to make this work.)  It seems that grub
calls the HDIO_GETGEO ioctl on the dm device, but the dm driver returns
ENOTTY.  Grub then uses its own weird defaults (620/128/63 CHS), causing
all attempts to read beyond the 2.4GB mark fail.

My question is, would it be acceptable to implement HDIO_GETGEO for dm
devices?  I realize that this CHS geometry is all nonsense anyway, but
it seems that we could at least try to help out grub/fdisk/etc on the
odd chance that someone wants a bootable dmraid array.

Granted, a workaround would be to create a 100MB /boot partition, but
since grub can boot off regular disks that are >2GB, it seems to me that
it ought to be able to do the same with a fakeraid array.

If I've just volunteered to write a patch by asking this question, I'm
ok with that too. :)

Thanks,

--Darrick
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