Re: [PATCH 1/2] qemu_capabilities: Introduce QEMU_CAPS_X_USE_CANONICAL_PATH_FOR_RAMBLOCK_ID

On Tue, Jan 12, 2021 at 20:24:44 +0100, Igor Mammedov wrote: [...] It really depends on the situation, because the commit messages don't seem to describe it satisfactory. Basically we don't want to ever use a qemu property knob, which is qemu free to change arbitrarily. If the property is to be used with any upcoming qemu version we must get a guarantee that it will not change. There are two options basically: 1) 'x-' is dropped 1a) we will use it with qemu-6.0 and later ( everything is clean, but users will have to update qemu to fix it ) 1b) we will carry code which will use 'x-' prefixed version from it's inception until qemu-5.2, when we will hard-mask it out and add plenty comments outlining that this is not what we do normally (it will be okay for past releases, since they will not change) 2) qemu declares the option stable with the 'x-' prefix We'll require that any place even in the code which declares the option has an appropriate comment preventing anybody from changing it. We'll then add also cautionary comments discouraging use of it. 3) qemu fixes the issue without libvirt's involvment For us really 1a) and 3 is acceptable without any comments. Other options will require extraordinary measures to prevent using this as prior art in using any other x-prefixed features from qemu. in 1a) case, downstreams can obviously backport the qemu patch renaming the feature and libvirt will require no change at all Now the question is whether we want to make migration work between the affected releases which will depend what to use.