[libvirt] [Qemu-devel] [PULL 25/26] block: Remove deprecated -drive option serial

[Cornelia Huck]

On Mon, 9 Jul 2018 08:58:05 +0200
Thomas Huth <thuth at redhat.com> wrote:

> On 06.07.2018 13:11, Cornelia Huck wrote:
> > On Wed, 4 Jul 2018 17:14:02 +0100
> > Peter Maydell <peter.maydell at linaro.org> wrote:
> >   
> >> On 4 July 2018 at 14:34, Kevin Wolf <kwolf at redhat.com> wrote:  
> >>> Essentially, what is important to me isn't getting these options dropped
> >>> exactly in 3.0, but not setting a bad precedence that deprecation isn't
> >>> actually worth anything. We may easily end up with this deprecation
> >>> process:
> >>>
> >>> depreate a feature
> >>> release QEMU version n + 1
> >>> release QEMU version n + 2
> >>> remove the feature
> >>> while libvirt hasn't removed use of the feature:
> >>>     # ...and why should it when everything is still working?
> >>>     reinstate the feature
> >>>     release QEMU version n + x
> >>>     remove the feature    
> >>
> >> My take on the deprecation policy essentially is that it gives
> >> us a *minimum* bar for how soon we can drop something. We
> >> shouldn't be using it as an "always target this speed for
> >> dropping something" -- we ought to be pragmatic. We can
> >> drop stuff that's unused quickly, but should be slower
> >> for things that still have major users (or reconsider
> >> the deprecation entirely, potentially). There should be
> >> a balance between making our work as developers easier and
> >> inconveniencing our users.  
> > 
> > What about the following?
> > 
> > - put a feature on the "normal" deprecation list to remove after two
> >   releases
> > Case (a): nobody complains, either within the deprecation period or
> > when it is finally removed  
> >   -> all is good  
> > Case (b): the feature turns out to be widely used, and/or it turns out
> > that it offers value that currently can't be offered easily in another
> > way  
> >   -> remove from deprecation list; this obviously needs more thinking  
> > Case (c): the feature is used, the users are willing to move away from
> > it, but they need a bit more time  
> >   -> put it on a "deprecation watchlist", listing the users we are  
> >   waiting for, and then remove after all are done (no +2)  
> 
> That sounds like another indication that we should have a list of
> "legacy" options in our qemu-doc, i.e. a list of interfaces that we
> consider as old and unwanted, but do not intend to remove in 2 releases
> yet. That idea has recently also come up already when we discussed the
> "-enable-kvm" and "-no-kvm" options. The remainders "-usbdevice" is also
> another good candidate for that list...

Agree. It also might be a good idea to poke e.g. libvirt about those.

Related: Are there other widely-used management etc. programs that make
use of QEMU? (For some value of 'widely'.) We might consider poking
them as well.