grub (v1) in f18?

[Richard W.M. Jones]

On Thu, Dec 06, 2012 at 03:25:21PM -0700, Chris Murphy wrote:
> 
> On Dec 6, 2012, at 3:02 PM, "Richard W.M. Jones" <rjones at redhat.com> wrote:
> 
> > On Thu, Dec 06, 2012 at 03:34:23PM -0500, Matthew Miller wrote:
> >> The grub2 package obsoletes grub, so there's no way to actually _use_ the
> >> older package, but it's still in the tree. Is there a reason?
> > 
> > Yes, virtualization.
> > 
> > I actually thought grub had been removed, so I removed the dependency
> > on it in libguestfs.  However libguestfs certainly *could* use grub,
> > if it was available.  There's some heated discussion of this here:
> > 
> > https://bugzilla.redhat.com/show_bug.cgi?id=737261#c10
> > 
> > and also in the archives of the current mailing list.
>
> Why is a boot manager needed for a virtualized guest? It seems like
> all you need is to point to a virtual disk (or current or past
> snapshot) and go directly to loading the kernel.
>
> If I could stuff < 1024 bytes of boot loader into ext4's two boot
> sectors, that seems ways easier than dealing with grub.
> http://lists.fedoraproject.org/pipermail/devel/2012-December/174786.html

Well this is a more general question about virtualization.  I agree
that it's sometimes more convenient to use an external kernel and
initrd to boot a guest, and libvirt supports this mode (see the
<kernel> and <initrd> in libvirt XML).  But:

(a) My understanding is this doesn't eliminate the need for a BIOS,
because I think early kernel code still calls into the BIOS, or at
least uses BIOS-created structures (eg. E820).  It does however
eliminate the need to deal with grub.

(b) Maintaining a separate kernel and initrd outside the VM is a pain
when it comes to updates.  How is 'yum' running in a VM supposed to
update a kernel stored outside the VM?

(c) It's generally better to remain as close as possible to baremetal,
just for ease of testing, reduced number of code paths, etc.

Note that none of this helps with libguestfs + grub.  We want grub so
we can deal with existing guests, and they're already using grub
whether we like it or not :-(

> And if there's a use case for UEFI VM's, why not use EFISTUB instead of grub?

No idea sorry.

Rich.

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