Re: [gentoo-dev] [RFC] More reliable hiding preserved libraries

["Tiziano Müller" <dev-zero@gentoo.org>]

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Am Sonntag, den 04.04.2010, 23:44 -0700 schrieb Brian Harring:
> On Mon, Apr 05, 2010 at 08:16:42AM +0200, Maciej Mrozowski wrote:
> > Unconditionally removing libraries (instead of preserving them) and making 
> > their reverse runtime dependencies reinstalled is unacceptable because 
> > "emerge" process involving multiple packages is not atomic. Simple as that.
> > Is this what you suggest? Correct me if I'm wrong:
> > 1. Users wants to uninstall or reinstall package, we let him do it provided 
> > reverse runtime dependencies are satisfied afterwards. Let's say he wants to 
> > upgrade expat.
> > 2. Expat SOVERSION changed meanwhile but package was not SLOTtted and runtime 
> > reverse deps will still be satisfied when we upgrade.
> > 3. Expat has been upgraded sucessfully,
> > 4a. "emerge" discovers reverse runtime dependencies are broken and it starts 
> > to rebuild them, then it bails out due to error ld: libexpat.so.<sth> not 
> > found. Because step 3 cannot be rolled back (no atomicy) - game over.
> > or
> > 4b. "emerge does not discover those and does nothing. python is broken so 
> > emerge cannot be used anymore. Game over
> 
> This is called 'nondeterministic resolution'- known issue also w/ 
> proposals of that sort.
> 
> Pretty much everytime someone proposes it as a solution, it gets 
> smacked down by most folk since an emerge -p invocation that is a 
> single pkg upgade shouldn't be able to go rebuild your entire world.
> 
> The alternative is a slotted ABI var- basically a counter (although it 
> doesn't have to be) w/in ebuilds themselves to indicate if they're 
> carrying a new ABI from upstream for that slotting.  For example, 
> you've got EXPAT merged w/ ABI=2, version 2.0.  version 2.0.1, for 
> whatever reason, breaks ABI- thus v2.0.1 in the tree is ABI=2.0.1 (or 
> 3, as said it's an arbitrary value).
> 
> Via that, the resolver can see that a rebuild is necessary and plan a 
> rebuild of all consumers (whether NEEDED based or revdep).  Note 
> preserve-lib would be rather useful here- specifically holding onto 
> the intermediate lib while doing rebuilding.
No, it doesn't help since you may have the same problems some people try
to solve in this thread.

>   This however breaks down 
> a bit when the ABI change is in reverse of normal versioning.
How so? Such a var should just specify the ABI and the PM only has to
check whether it changed from one PVR to the other. The "how" is
completely irrelevant.


-- 
Tiziano Müller
Gentoo Linux Developer
Areas of responsibility:
  Samba, PostgreSQL, CPP, Python, sysadmin, GLEP Editor
E-Mail   : dev-zero@gentoo.org
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