Re: Future of Wireshark's shared library ABI stability

[Bálint Réczey <balint () balintreczey hu>]

João Valverde <j () v6e pt> ezt írta (időpont: 2022. jan. 21., P, 1:29):
> On 20/01/22 21:24, Bálint Réczey wrote:
> > Hi Guy,
> >
> > Guy Harris <gharris () sonic net> ezt írta (időpont: 2022. jan. 20., Cs, 21:52):
> > > On Jan 20, 2022, at 12:34 PM, Gerald Combs <gerald () wireshark org> wrote:
> > >
> > > > Q: Should *wsutil* be part of that stable ABI?
> > > >
> > > > Debian, Ubuntu and (according to rpmfind.net) OpenSuSE and Mageia treat it as such. It would be helpful to know 
> > > > what non-Wireshark packages depend on wsutil in those distributions and elsewhere.
> > > ...and, if there are any, to know *why*.
> > It seems libvirt's plugin needs wmem_alloc(), for example:
> > https://gitlab.com/wireshark/wireshark/-/issues/17889
>
> How is that relevant?
>
> The answer to the question that was asked is: exactly zero Debian
> packages have a dependency on your libwsutil/libwireshark/libwiretap
> packages.

In gitlab issue I already mention libvirt as a packaged thus I had the
impression that this one was covered:
https://gitlab.com/wireshark/wireshark/-/issues/17822#note_815677078

It is factually incorrect to state that nothing depends on our
libraries in Debian:

root@73c5830ef791:/# apt-cache rdepends libwireshark14
libwireshark14
Reverse Depends:
...
  libvirt-wireshark
root@73c5830ef791:/# cat /etc/issue
Debian GNU/Linux 11 \n \l

root@b396a73800b0:/# apt-cache rdepends libwireshark15
libwireshark15
Reverse Depends:
...
  libvirt-wireshark
root@b396a73800b0:/# cat /etc/issue
Debian GNU/Linux bookworm/sid \n \l

# apt-cache show libvirt-wireshark
Package: libvirt-wireshark
Source: libvirt
...
Description: Wireshark dissector for the libvirt protocol

I'm not sure how you checked, but this is what I saw on current stable and sid.

> If you want to see what a properly packaged non-trivial application for
> Debian looks like check out Geany[1] for example. It also uses shared
> libraries internally and has a plugin system.

Generally I'm open to learn new things, but after not being able to
find reverse dependencies of libwireshark* I hope you don't mind that
I take your advice on packaging with a grain of salt.

From Geany's description:

About ----- Geany is a small and lightweight integrated development
environment. It was developed to provide a small and fast IDE, which
has only a few dependencies from other packages. Another goal was to
be as independent as possible from a special Desktop Environment like
KDE or GNOME. So it is using only the GTK+ toolkit and therefore you
need only the GTK+ runtime libraries to run Geany.

As you can see Geany's goals are very different from Wireshark's and
Geany not providing shared libraries aligns with having minimal
dependencies.

Speaking of packaging non-trivial applications I maintained systemd
and glibc among other things in Ubuntu in the last few years thus I
have some experience in the area.

> > IMO it is easier mentally to have a single library ABI policy because
> > we ship only public libraries. Having a more relaxed private shared
> > library policy would make it easier to make mistakes.
>
> I have no idea what you are trying to say here. The libraries were not
> intended to be public until you stepped in, by the way.

I'm wondering if others did understand what I tried to say here.

As you pointed out in [2] there were recurring queries to make the
then private libraries more widely available and I accept the credit
or blame to help a lot in making the ABI stable and available for
external projects.

> > Also if libwsutil (with wmem_alloc) became private in 3.6.x then
> > libvirt had a much harder time continuing the maintenance of their
> > plugin starting with 3.6.0.
>
> No. Nobody said anything about 3.6.x and none of that is true.

This was a hypothetical example of what would happen if we moved
libwsutil to a private library location with no ABI stability promise.
And wmem_alloc did move to libwsutil in [3].

Thanks,
Balint

> [1] https://salsa.debian.org/geany-team/geany
[2] https://gitlab.com/wireshark/wireshark/-/issues/17822#note_815838497
[3] https://gitlab.com/wireshark/wireshark/-/commit/7f9c1f5f92c131354fc8b2b88d473706786064c0
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