On Mon, Jun 23, 2014 at 07:42:27PM -0600, Warner Losh wrote:
> On Jun 23, 2014, at 7:12 PM, Glen Barber <g...@freebsd.org> wrote:
> > On Mon, Jun 23, 2014 at 06:57:15PM -0600, Warner Losh wrote:
> >> On Jun 23, 2014, at 6:15 PM, Craig Rodrigues <rodr...@freebsd.org> wrote:
> >>> So, I guess that stable/9 can build properly on a stable/10 box.
> >>> For FreeBSD 9.2, there is no easy way out.
> >> 
> >> You’ll have to back port the patch then. We don’t guarantee forward
> >> compatibility like this since 9.2 is frozen in time now.
> >> 
> > 
> > I'd really like to discuss rethinking our forward-compatibility
> > policies, since we have (now) 3 active stable/ branches, plus head/. 
> Generally, in the past, the rule has been “head will build from the last 
> stable branch tip.” This was extended, for a while, to “last stable branch 
> point” when Ruslan made sure that worked. While -stable has generally built 
> on -head, this was never part of the contract. It usually did, but is very 
> very hard to guarantee given the nature of head’s tools changing in ways that 
> are allowed for head, but that break prior branches.

I sort of typed what I meant a bit backwards from what I intended to
write.  What I meant (sort of) is, "I would like to discuss our forward
thinking on backward-compatibility."

I fully understand forward-compatibility is not feasible.

> > What I would like to see, with my RE hat on, is a "best effort"
> > backwards compatibility to being able to build the lowest-numbered
> > supported stable/ branch on head/.
> I think, that as in the past, this will generally work. However, it won’t 
> always work. Things break in this area a lot. More than you might think, 
> especially with the huge amount of churn we’ve had wrt compilers, make, etc. 
> I suspect that new imports of clang will break this every time, since every 
> import of clang has required changes to the tree to either disable warnings, 
> or to fix newly flagged things. I suspect there will be a lot of churn here, 
> and releases will go stale the fastest… With -current starting to support 
> building multiple versions of clang (and gcc), there’s hope for the future, 
> but back-porting this code is beyond what I have the time to do. That’s going 
> to make things increasingly difficult as we march forward.

I hate to even suggest this, but the ports tree (ab)uses the notion of
using the kern.osreldate for certain things.  This, however, requires
proper bumping of __FreeBSD_version when needed, and maintenance of the
Makefiles for the kern.osreldate-specific things.

The benefit to this is that it would help prevent pissing off ports
developers and make their lives a bit easier when userland / kernel
things change.  It would, however, (expectedly) is that it would force
src committers to do the right thing.  Win-win, IMHO.

> This isn’t even getting into cross build scenarios….
> Or building releases, which is a whole different set of lightly tested code 
> that is mostly host independent, but sometimes isn’t as much as you’d had 
> hoped...
> > Sure, this won't always work, but "best effort" is better than "no
> > effort", which the latter is why we do not have stable/8 snapshot
> > builds, to be honest.  I won't spend the time on the stable/8/release/
> > code nor the snapshot build scripts to waste the time.  Building
> > stable/9 on head/ is annoying alone.
> stable/9 builds on head. If there’s a race, that needs to be fixed in 
> stable/9. That’s quasi supported because people do it. The “best effort” 
> involves people that are interested in the bugs being fixed fixing them, or 
> convincing others to fix them. For me, this scenario is outside the area I 
> care about, have the ability to test, or have time for.
> So “best effort” involves more than me making an effort. I may or I may not. 
> It all depends on my time and inclination. If it is going to work, bugs need 
> to be fixed in stable/9 that prevents it from building on head, while not 
> breaking the ability to build on 9. So there’s a lot of heavy lifting that 
> will be needed in short order to keep this working once the clang folks can 
> figure out how to get past the angst of the upgrade path and push forward to 
> 3.5. Some architectures will break when that happens, no doubt.

Personally, and no I won't discuss more on this, I'm in the camp of "I
don't really see clang as a feature."  It caused our ports developers
and maintainers a mountain of headache to convert to the "invisibly new
great thing", it increases our overall buildworld by a non-insignificant
amount of time, and it has personally caused me headaches (still
ongoing) trying to figure out what the correct incantation of evil to
wish over the cauldron to get BeagleBone images to build.  (They're
failing because gcc is not being installed on both head/ and stable/10/,
and despite the game of "musical KNOBS" I've been playing over the past
few days, I'm running out of hair to pull out of my head.)

> But 9.2 will never build on head because it is broken with bmake, which is 
> now standard for head. Since 9.2 cannot be changed, and since we’ve removed 
> (or nearly) fmake in current, chances are quite good it will never build on 
> head again without some special handling.
> In summary, good luck! there’s a lot of use cases here, and it will take time 
> and effort of multiple people over the long haul to keep it working. Best 
> effort may be larger than you estimate… I won’t stand in your way, but I’m 
> afraid my time available to help is limited.

As Ozzy once sang:

    "I'm just a dreamer
    I dream my life away
    I'm just a dreamer
    Who dreams of better days"


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