Re: [PATCH v2] docs: specify stability of hypfs path documentation

[Jürgen Groß <jgross@xxxxxxxx>]

On 16.07.20 13:24, Jan Beulich wrote:
> On 16.07.2020 12:31, Jürgen Groß wrote:
> > On 16.07.20 12:11, Jan Beulich wrote:
> > > On 15.07.2020 16:37, George Dunlap wrote:
> > > > IT sounds like you’re saying:
> > > >
> > > > 1. Paths listed without conditions will always be available
> > > >
> > > > 2. Paths listed with conditions may be extended: i.e., a node currently listed 
> > > > as PV might also become available for HVM guests
> > > >
> > > > 3. Paths listed with conditions might have those conditions reduced, but will never 
> > > > entirely disappear.  So something currently listed as PV might be reduced to 
> > > > CONFIG_HAS_FOO, but won’t be completely removed.
> > > >
> > > > Is that what you meant?
> > > I see Jürgen replied "yes" to this, but I'm not sure about 1.
> > > above: I think it's quite reasonable to expect that paths without
> > > condition may gain a condition. Just like paths now having a
> > > condition and (perhaps temporarily) losing it shouldn't all of
> > > the sudden become "always available" when they weren't meant to
> > > be.
> > >
> > > As far a 3. goes, I'm also unsure in how far this is any better
> > > stability wise (from a consumer pov) than allowing paths to
> > > entirely disappear.
> > The idea is that any user tool using hypfs can rely on paths under 1 to
> > exist, while the ones under 3 might not be there due to the hypervisor
> > config or the used system.
> >
> > A path not being allowed to entirely disappear ensures that it remains
> > in the documentation, so the same path can't be reused for something
> > different in future.
> And then how do you deal with a condition getting dropped, and
> later wanting to get re-added? Do we need a placeholder condition
> like [ALWAYS] or [TRUE]?
Dropping a condition has to be considered very carefully, same as
introducing a new path without any condition.

In worst case you can still go with [CONFIG_HYPFS].


Juergen