Re: [Qemu-devel] QEMU etc/e820 and fw_cfg

[Gerd Hoffmann]

On Di, 2015-03-03 at 10:32 +0000, Gordan Bobic wrote:
> I need to pass a custom e820 map to a virtual machine for
> troubleshooting purposes and working around IOMMU hardware
> bugs.
> 
> I have found references to a custom map being providable
> via an external file, mentioned as "etc/e820" and "fw_cfg".

That is the (filesystem-like) interface between qemu and firmware
(seabios usually), it doesn't refer to a on-disk file.

> Unfortunately, I have not found any documentation that
> explains how to use this from userspace when invoking
> qemu.

You can't.

Passing a different e820 map requires patching qemu (or seabios, which
mangles the e820 table to add reservations for acpi etc).

What exactly do you need?

cheers,
  Gerd