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  • From: Remko van der Vossen <wich AT yuugen.jp>
  • To: Thomas Orgis <thomas-forum AT orgis.org>
  • Cc: sm-discuss AT lists.ibiblio.org
  • Subject: Re: [SM-Discuss] About libpng-1.6 migration
  • Date: Sun, 6 Mar 2016 20:59:09 +0100

Hi guys,

Last week I've been experimenting with a new version of UP_TRIGGERS for
libpng. In it I don't just check all shared objects for libpng dependencies,
but also the .la files. Finally, I just straight out dispel anything that
depends on libpng and trigger new casts for them. This irons out a number of
the cyclic dependencies as we have some safeguards in the DEPENDS files of
various spells to disable some optional dependencies when some spells are not
already installed. But that of course only works when they aren't actually
installed, hence the straight out dispel of them.

This has been working well on two of my systems, I was able to switch back
and forth between v1.2 and v1.6 without issue. Three points of note though;
1. I run pretty lean systems, someone with some heavier installs e.g. with
desktop environments should give it a go as well and check for remaining
fallout
2. You may lose some features in the spells you had installed as some
features are disabled in the DEPENDS files to avoid some cyclic dependencies
3. If things don't go as planned, then you will lose part of your installed
spells. One needs to be vigilant and keep a list of the dispelled spells
around so you can recast them when things don't work out. To this end I put a
bail-out query in the UP_TRIGGERS that defaults to no, so that no mistakes
can occur.

I'm not sure I have access to the box that has these changes at the moment,
so it'll probably be next week that I commit them.

Regards, Remko

> On 2016/03/06, at 19:58, Thomas Orgis <thomas-forum AT orgis.org> wrote:
>
> Hi,
>
> just one note after converting my last install to the current
> libpng-1.6: There is always lots of fallout. Even after dealing with
> the true issues about cyclic stuff depending on each other and on
> differing versions of libpng, a large part of breakage results out of
> libtool files mentioning -lpng12 and leading spells needlessly to link
> that in together with -lpng or -lpng16. Yep, you might get binaries
> depending on _both_ PNG libs, even if they actually don't. That is
> happily prevented by libtool bailing out during the final linking stage
> since it of course cannot find a -lpng12 to link to.
>
> My solution, to get on track after multiple frustrating attempts to
> rebuild stuff and cursing because -lpng12 crops up again and again, was
> to finally just delete all .la files that contained png12 in them.
> After all, for dynamic linking, we don't need them. Then one can try to
> recast all that stuff and hope that libpng12 is gone for good some time.
>
> That's actually an argument not to provide a compatibility spell with a
> libpng12.so. You'd end up with binaries actually being linked to both
> libs (which probably will also fail … or it even might succeed!).
>
> Maybe we can offer some help to users trying to upgrade from the last
> stable grimoire … a script that tells the user which spells
>
> a) have binaries installed that still link to libpng12
> b) have .la files mentioning -lpng12
>
> Those should be queued and recast in most likely many iterations
> because things break depening subtly on order, until no traces are left
> of the old lib. Perhaps this needs to be something to go along with
> cleanse, only more brutal. Exorcise.
>
>
> Alrighty then,
>
> Thomas
>
> PS: Part of the fallout of updating things is that now my user is not
> allowed to access /dev/dri/card0 anymore. Some udev rules got lost … ?
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