[Qemu-devel] Guest kernel device compatability auto-detection

[Sasha Levin <levinsasha928@gmail.com>]

Hi,

Currently when we run the guest we treat it as a black box, we're not
quite sure what it's going to start and whether it supports the same
features we expect it to support when running it from the host.

This forces us to start the guest with the safest defaults possible, for
example: '-drive file=my_image.qcow2' will be started with slow IDE
emulation even though the guest is capable of virtio.

I'm currently working on a method to try and detect whether the guest
kernel has specific configurations enabled and either warn the user if
we know the kernel is not going to properly work or use better defaults
if we know some advanced features are going to work.

How am I planning to do it? First, we'll try finding which kernel the
guest is going to boot (easy when user does '-kernel', less easy when
the user boots an image). For simplicity sake I'll stick with the
'-kernel' option for now.

Once we have the kernel we can do two things:
 1. See if the kernel was built with CONFIG_IKCONFIG.

 2. Try finding the System.map which belongs to the kernel, it's
provided with all distro kernels so we can expect it to be around. If we
did find it we repeat the same process as in #1.

If we found one of the above, we start matching config sets ("we need
a,b,c,d for virtio, let's see if it's all there"). Once we find a good
config set, we use it for defaults. If we didn't find a good config set
we warn the user and don't even bother starting the guest.

If we couldn't find either, we can just default to whatever we have as
defaults now.


To sum it up, I was wondering if this approach has been considered
before and whether it sounds interesting enough to try.

-- 

Sasha.