[libvirt] What to do about the qemu "-boot strict" option

[Jiri Denemark]

On Wed, Nov 27, 2013 at 14:37:02 +0200, Laine Stump wrote:
> Awhile back a bug was filed against libvirt about the inability to
> completely exclude a disk from the boot order:
> 
>    https://bugzilla.redhat.com/show_bug.cgi?id=888635
> 
> In short, you can't have a domain that used PXE to boot, but also has an
> un-bootable disk device *even if that disk isn't listed in the boot
> order*, because if PXE times out (e.g. due to the bridge forwarding
> delay), the BIOS will move on to the next target, which will be the
> unbootable disk device (again - even though it wasn't given a boot
> order), and get stuck at a "/BOOT DISK FAILURE, PRESS ANY KEY" message
> /until a user intervenes.
> 
> It was obviously beyond the ability of libvirt to fix this (although it
> can be worked around by creating a very small disk image with a
> bootloader that merely instructs the system to reboot, and placing
> *that* disk in the boot order just after the PXE device), so the BZ was
> closed as CANTFIX.
> 
> A couple days ago I noticed that Amos Kong had later actually fixed this
> problem in seabios and qemu:
> 
>    https://bugzilla.redhat.com/show_bug.cgi?id=888633
>    https://bugzilla.redhat.com/show_bug.cgi?id=903204
> 
> Existing behavior is preserved though, and the new behavior only comes
> about if "-boot strict" is specified on the qemu commandline.
> 
> It definitely seems desirable to have this ability in libvirt, but I'm
> almost of the opinion that this should *always* be the behavior (if you
> want all devices to be in the boot order, you can just give all of them
> (or none of them, if you're feeling adventurous) a boot order ranking).
> But I thought it would be prudent to ask opinions about that before
> making any patch.
> 
> So what are the opinions? Should the "if any devices are given a boot
> order, only attempt to boot from devices that have a boot order
> specified" behavior just be the default (and only) behavior when
> qemu/seabios supports it? (this would imply that the old behavior is
> just a bug)? Or do we need to make it configurable?

I would consider the old behavior as a bug and just use -boot strict
whenever we can.

Jirka