[sane-devel] backend naming conventions/constraints

[Olaf Meeuwissen]

Henning Meier-Geinitz <henning at meier-geinitz.de> writes:

> On Fri, Feb 28, 2003 at 08:50:44PM +0900, Olaf Meeuwissen wrote:
> > I tried getting things to work with a hyphenated backend name, but to
> > no avail.  The dll backend uses the literal name in dll.conf to check
> > for functions in the backend :-(
> 
> What would be the alternative? How should it get the internal
> backend name?

Replace any character that is not valid in a C identifier with `_'?
The Makefile.in's could use the same convention and use

  -DBACKEND_NAME=$(shell echo $* | sed 's,[^_a-zA-Z0-9],_,g')

The BACKEND_NAME is prefixed with sane_, so you don't need to worry
about backend names that start with a digit.

> > Some minor mods in the dll backend could easily fix that (I'd think),
> > but since I have to rely on existing sane-backends packages out there
> > that is not an option for me right now.  I'll go with epkowa for the
> > backend.
> 
> Sounds fine for me.

Eh, that is I'll go with "epkowa" modulo objections from higher up the
foodchain (management and the like).

> Keep in mind that attaching to a sane  backend is quite flexible.
> That's the reason for some of the tricks used in the Makefile.
> 
> 1) static linking
>   a) link to one backend statically (e.g. net). The symbold must be
>      sane_init () (without backend name) for this to work.
>   b) link to libsane-dll.a which includes (preloads) all backends
>      statically. The api symbols must use e.g. sane_mustek_init () to 
>      avoid duplicated symbols.
> 2) shared libraries
>   a) link to any sane backend as shared library. The symbol names must
>      be sane_init(). The so name of the library must be libsane.so
>      (not libsane-mustek.so), otherwise you can't change the backend
>      after linking. That's the reason for the change in libtool.
>   b) link to libsane-dll.so as a shared libryry which preloads all
>      other backends (see above).
> 3) dynamic loading
>  link to libsane-dll.so which loads all other backends dynamically.
> 
> I'm open for changes but it's not as easy as it looks on first sight.

I've only changed the way a file name is mapped to a BACKEND_NAME, so
I would say it's okay.  But then again, I am not familiar with all the
little hacks to get the above to work ;-)
As far as I can see, only the dll backend needs to do the same.
-- 
Olaf Meeuwissen                            EPSON KOWA Corporation, ECS
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Penguin's lib!       -- I hack, therefore I am --               LPIC-2