[Libguestfs] supermin init segfaults when kernel has large modules

[Richard W.M. Jones]

Continuing the discussion from:
https://bugzilla.redhat.com/show_bug.cgi?id=1339691#c17

[Luiz: There's no need to subscribe to the mailing list, once I've
moderated your first message the others will go through.]

> IMO, supermin should use the kernel the host is running as a hint and
> try that one first. This shouldn't be hard to do.
>
> This BZ should be enough evidence that picking up the highest numbered
> kernel is not a good design decision. My kernel was a test kernel with
> custom patches, I was just lucky it didn't blow at boot.

What we really want is to pick a kernel that will definitely boot on
qemu.  It's not clear this is always going to be either the highest
numbered kernel (for reasons you outline) nor the running kernel
(because the host kernel may not include virtio drivers - a problem on
Ubuntu sometimes because it has special virt kernels).

This is a tough problem, but we could do better than we are doing now.

For example we could check the kernels to ensure they have virtio and
the other devices we need enabled (eg. using /boot/config-*) and
discard any kernels from the list which do not.

We might also consider excluding kernels based on a blacklist of
version numbers, since kernels are sometimes released which simply
don't boot on qemu.

The current code has been picking the highest numbered non-Xen kernel
for the last 7 years, and while it generally works fine it does
occasionally cause trouble like this.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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