This is a I found some time ago using google, unfortunately I don't
remember original author. I had rewritten the patch (original file for
some reason was malformed) and changed device id of emulated
controller to match the one found in my plan9.iso.

However, I only tested (and written it) using modified qemu sources
from kvm-16 distribution, so I don't if it works with stock qemu-0.9.

The patch is very simple, it only supports hard drives and doesn't
have a SCSI BIOS (There's sign for preparing a better one in qemu
code), however, it works and i have a functional installation using
emulated 2GB scsi hd with floppy boot. The only thing is that 9pcf
kernel from somewhere around february stops when starting rc, using an
old (ca. 2005?) kernel solved it. 9pccd works flawlessly.

I think there was some speedup compared to emulated IDE, however,
Plan9 installation in qemu (I don't count my test install on old pc,
as it was with old iso) for some reason is still veeeryy slow. I think
it's userspace problem, since most of the time there's _no_ disk
activity at all during "copydist". Since IO works fine for everything
other than installer, I am very confused. I had the same 'slow
install' problem every time I had installed Plan9 (That includes pc
with i440bx and ATA33 7200rpm drive, netbsd-xen0 with lsi53c895 and
7200 SCSI hd and many tries under both VMWare and Qemu).

Now, off to change terminal into cpu server....

-- 
Paul Lasek