On Wed, Nov 27, 2013 at 02:37:02PM +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.
We have a reboot-timeout boot parameter to reboot guest if not found bootable device. | commit ac05f3492421caeb05809ffa02c6198ede179e43 | Author: Amos Kong <akong@redhat.com> | Date: Fri Sep 7 11:11:03 2012 +0800 | | add a boot parameter to set reboot timeout | | Added an option to let qemu transfer a configuration file to bios, | "etc/boot-fail-wait", which could be specified by command | -boot reboot-timeout=T | T have a max value of 0xffff, unit is ms. | | With this option, guest will wait for a given time if not find | bootabled device, then reboot. If reboot-timeout is '-1', guest | will not reboot, qemu passes '-1' to bios by default. | | This feature need the new seabios's support. | | Seabios pulls the value from the fwcfg "file" interface, this | interface is used because SeaBIOS needs a reliable way of | obtaining a name, value size, and value. It in no way requires | that there be a real file on the user's host machine. | | Signed-off-by: Amos Kong <akong@redhat.com> | Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> |
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).
We leave the default as off just for compatibility with old qemu. For libvirt code, you can always use "strict=on"
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? If it needs to be configurable, the boot-related xml seems to be a bit unorganized (a flat list of elements with mostly a single attribute for each), but I suppose this could be added as a new attribute to the <bios> element...
-- Amos.