Re: [dpdk-dev] [PATCH] mk: fix missing link of librte_vhost in shared, non-combined config

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2015-02-16 12:01, Panu Matilainen:
> On 02/13/2015 03:18 PM, Thomas Monjalon wrote:
> > 2015-02-13 12:33, Panu Matilainen:
> >> On 02/13/2015 11:28 AM, Thomas Monjalon wrote:
> >>> 2015-02-13 09:27, Panu Matilainen:
> >>>> On 02/12/2015 05:44 PM, Thomas Monjalon wrote:
> >>>>> A library is considered as a plugin if there is no public API and it
> >>>>> registers itself. That's the case of normal PMD.
> >>>>> But bonding and Xen have some library parts with public API.
> >>>>> It has been discussed and agreed for bonding but I'm not aware of the Xen case.
> >>>>
> >>>> Fair enough, thanks for the explanation.
> >>>>
> >>>> Just wondering about versioning of these things - currently all the PMDs
> >>>> are versioned as well, which is slightly at odds with their expected
> >>>> usage, dlopen()'ed items usually are not versioned because it makes the
> >>>> files moving targets. But if a plugin can be an library too then it
> >>>> clearly needs to be versioned as well.
> >>>
> >>> Not sure to understand your considerations.
> >>> Plugins must be versioned because there can be some incompatibilities
> >>> like mbuf rework.
> >>
> >> Plugins are version-dependent obviously, but the issue is somewhat
> >> different from library versioning. Plugins are generally consumers of
> >> the versioned ABIs, whereas libraries are the providers.
> >>
> >>>> I'm just thinking of typical packaging where the unversioned *.so
> >>>> symlinks are in a -devel subpackage and the versioned libraries are in
> >>>> the main runtime package. Plugins should be loadable by a stable
> >>>> unversioned name always, for libraries the linker handles it behind the
> >>>> scenes. So in packaging these things, plugin *.so links need to be
> >>>> handled differently (placed into the main package) from others. Not
> >>>> rocket science to filter by 'pmd' in the name, but a new twist anyway
> >>>> and easy to get wrong.
> >>>>
> >>>> One possibility to make it all more obvious might be having a separate
> >>>> directory for plugins, the mixed case ccould be handled by symlinks.
> >>>
> >>> I think I don't understand which use case you are trying to solve.
> >>
> >> Its a usability/documentation issue more than a technical one. If plugin
> >> DSO's are versioned (like they currently are), then loading them via eg
> >> -d becomes cumbersome since you need to hunt down and provide the
> >> versioned name, eg "testpmd -d librte_pmd_pcap.so.1 [...]"
> >>
> >> Like said above, it can be worked around by leaving the unversioned
> >> symlinks in place for plugins in runtime (library) packages, but that
> >> sort of voids the point of versioning. One possibility would be
> >> introducing a per-version plugin directory that would be used as the
> >> default path for dlopen() unless an absolute path is used.
> >
> > It makes me think that instead of using a -d option per plugin, why not
> > adding a -D option to load all plugins from a directory?
> 
> Are you thinking of "-D <plugindir>" or just -D (to use a build-time 
> hardwired directory)?

I'm thinking of "-D <plugindir>".
I understand you would like a "hardwired" default directory which would be
properly packaged by a distribution. Maybe that it could be a build-time
default to load all the plugins of a directory (without option). Then the
-d and -D options would overwrite the build-time default behaviour.