[gdal-dev] VSI handlers as plugin (shared library)

[Even Rouault]

Le lundi 02 novembre 2015 21:44:20, Ivan Lucena a écrit :
> Hi Even,
> 
> It doesn't seems like we are talking about the same think.

I think we do talk about the same thing :-)

> 
> A VSI handler is is not an GDAL/OGR driver, so I can't see how that would
> work.

Well, you can just pretend that your shared object is a module that contains a 
GDAL driver, but you don't need to put a GDAL driver in it. AutoLoadDrivers() 
doesn't check that a driver will be registered. It will just call the entry 
point.

So just try what I suggested: add a extern "C" GDALRegisterME() that calls 
your VSI handler installation, and you'll be done.

I've used this technique recently for the port/cpl_vsil_crypt.cpp module to 
make it work against OSGeo4W unmodified binaries.

> 
> A VSI Handler is registered at that code
> [https://trac.osgeo.org/gdal/browser/trunk/gdal/port/cpl_vsil.cpp#L1153].
> 
> I wrote my VSI code on /port and add a installation function to cpl_vsi.h
> and everything is working just fine when HAVE_OCI is detect by the
> makefiles.
> 
> But you gave me an idea, I could move my code from /port/cpl_vsil_XXX.cpp
> to /frmts/georaster/cpl_vsil_XXX.cpp and register it from there. If
> possible.
> 
> Then I would not need a VSI plugin, since the georaster driver plugin is
> the only user of my VSI handler.
> 
> Does it make sense?
> 
> Regards,
> Ivan
> 
> 
> ________________________________________
> From: Even Rouault <even.rouault at spatialys.com>
> Sent: Monday, November 2, 2015 3:09 PM
> To: gdal-dev at lists.osgeo.org
> Cc: Ivan Lucena
> Subject: Re: [gdal-dev] VSI handlers as plugin (shared library)
> 
> Le lundi 02 novembre 2015 20:58:59, Ivan Lucena a écrit :
> > Hi there,
> > 
> > 
> > What if we could build and distribute VSI handler as plugins?
> > 
> > 
> > I developed a VSI handler that depends on other software, so I would
> > rather not build the GDAL main library with that dependency and let the
> > user decided if they want to use the plugin or not.
> > 
> > 
> > We would need to have a code on cpl_vsil.cpp similar to AutoLoadDrivers()
> > from  gdaldrivermanager.cpp to load vsi_XXX.{so,dll} dynamically.
> > 
> > 
> > Would that be worth the effort? Any other cases where that could be
> > useful?
> 
> Ivan,
> 
> You don't need to change anything in GDAL, assuming that you call
> GDALRegisterAll() at some point. Just add a C function GDALRegisterMe() in
> your shared module, call the shared object gdal_XXXXXXX.so/dll and you're
> done.
> 
> Even
> 
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