Re: [libvirt] [RFC 0/7] Warn at runtime when deprecated features are used

On Fri, 2018-10-05 at 09:54 +0100, Daniel P. Berrangé wrote: > On Fri, Oct 05, 2018 at 10:34:33AM +0200, Jiri Denemark wrote: > > But what if QEMU (or any other hypervisor) marks something (device > > model, machine type) as deprecated and we use that deprecated value as > > our default. Shouldn't we be able to tell about it to our users (here > > runtime warnings could help) when they use such thing explicitly and > > choose a different default value? That would help users with the > > transition and once hypervisor drops support for it completely, fewer > > existing domains will be affected since the recently created ones would > > already use non-deprecated defaults. > > QEMU already emits warnings on stderr whenever something that is > deprecated is used, and those end up in the libvirt log file for > that guest. I don't think that we need to duplicate what QEMU > is already reporting again. Warnings printed on stderr -> users and developers will actually see them, be annoyed by them, eventually cave in and act upon them. Warnings written to a log -> nobody will notice them, until one day things suddenly stop working apparently out of the blue. We might pretend that's not the case, but really, it is.