[sane-devel] why my backend don't work?

[Henning Meier-Geinitz]

Hi,

On Wed, Jul 10, 2002 at 04:27:51PM +0800, zhu wrote:
>     I want to try a new backend which main file is m1200.c.  Other
>     files are m1200.h,m1200.conf,mscan.c and mscan.h.

Just a note: If you plan to include your backend into SANE later,
please change the names of at least the latter two files to e.g.
m1200-scan.* so it's easier to find out to which backend they belong.

>     I did as followed:
>     (1)Modified the backend/Makefile.in, added "m1200" in the list
>     following "PRELOADABLE_BACKENDS = " ;

That will compile m1200.c.

>     (2)Added "m1200.c m1200.conf m1200.h mscan.c mscan.h" in the list
>     following "DISTFILES = " ;

If you run "make dist", your backend will be added to
sane-backends-*.tar.gz. That's not needed for compilation.

>     (3)Added "libsane-m1200.la:
>     ../sanei/sanei_config2.lo","libsane-m1200.la:
>     ../sanei/sanei_constrain_value.lo"

That's ok, if you need these two objects in your backend.

>     (4)modified the "dll.conf",added "m1200"
>     (5)make uninstall    
>     (6)execute sane-backends-1.0.8/configure
>     (7)make (no error)
>     (8)make install (no error)

So compilation is ok, but...

>     My problem is ,when I type "scanimage -L",it says error ,error info is:
> 
>     scanimage:error while loading the shared libraries:
>     /usr/local/lib/sane/libsane-m1200.so.1:undefined symbol: funcname

runtime-linking failed. It's easier to find such errors if you use
"configure --disable-shared" (use static linking).

>     This "funcname" is a function declared in file mscan.h and
>     defined in mscan.c,and called in the function "sane_init". In the
>     file m1200.c ,I've not forgotten include the head file "mscan.h".

mscan.c is never compiled. The Makefile doesn't know about it. You
told the compiler: Hey, I have an external function "funcname" and I
will link the object file that includes the functions code. But you
didn't :-)

Two solutions:
1) Include mscan.c in m1200.c. Either by copying the code into that
   file or by using #include. Not that nice but the easiest solution.
2) Link the two files together. Have a look at canon_pp in the
   Makefile.in for an example, how to do it.
   
Keep in mind, that you shouldn't export functions, that don't start
with "sane_*" (the API-functions) or "sanei_*". And the symbols should
be unique. So if you use approach 2), you should name the xported
functions from mscan.c sumething like sanei_m1200_*.

When your backend works (at least to some degeree), we are interested
in which scanners it will support and where we can download it. We are
even more interested in a .desc file :-)

Bye,
  Henning