On 01.03.21 15:20, Igor Mammedov wrote: > On Mon, 1 Mar 2021 08:45:53 +0100 > Thomas Lamprecht <t.lampre...@proxmox.com> wrote: >> On 01.03.21 08:20, Michael S. Tsirkin wrote: >>> There are various testing efforts the reason this got undetected is >>> because it does not affect linux guests, and even for windows >>> they kind of recover, there's just some boot slowdown around >>> reconfiguration. >>> Not easy to detect automatically given windows has lots of random >>> downtime during boot around updates etc etc. >>> >> >> No, Windows does not reconfigure, this is a permanent change, one is just >> lucky >> if one has a DHCP server around in the network accessible for the guest. >> As static addresses setup on that virtual NIC before that config is gone, >> no recovery whatsoever until manual intervention. > Static IP's are the pain guest admin picked up to deal with so he might have > to > reconfigure guest OS when it decides to rename NICs. In this case moving > to new QEMU is alike to updating BIOS which fixed PCI description. > (On QEMU side we try to avoid breaking changes, but sometime it happens anyway > and it's up guest admin to fix OS quirks) >
heh, I agree, but users see it very differently, QEMU got updated, something stopped working/changed/... -> QEMU at fault. >> I meant more of a "dump HW layout to .txt file, commit to git, and ensure >> there's no diff without and machine version bump" (very boiled down), e.g., >> like >> ABI checks for kernel builds are often done by distros - albeit those are >> easier >> as its quite clear what and how the kernel ABI can be used. > ACPI tables are not considered as ABI change in QEMU, technically tables that > QEMU > generates are firmware and not version-ed (same like we don't tie anything to > specific firmware versions). > > However we rarely do version ACPI changes (only when it breaks something or > we suspect it would break and we can't accept that breakage), this time it > took > a lot of time to find out that. We try to minimize such cases as every > versioning knob adds up to maintenance. > > For ACPI tables changes, QEMU has bios-tables-test, but it lets us to catch > unintended changes only. > Technically it's possible to keep master tables for old machine versions > and test against it. But I'm not sure if we should do that, because some > (most) changes are harmless or useful and should apply to all machine > versions. > So we will end up in the same situation, where we decide if a change > should be versioned or not. > > OK, fair enough. Many thanks for providing some rationale!
