[sane-devel] Using "scanimage" under Gentoo

[Olaf Meeuwissen]

Hi Rainer,

Dr Rainer Woitok writes:

> Olaf,
>
> On Saturday, 2020-02-08 12:52:49 +0900, you wrote:
>
> [ "> >" refers to Bruce Schultz' mail ]
>
>> ...
>> > That fails now for me with the same error you error you had.
>>
>> For me too (on our CI's debian-10-full setup with 336cbdfd as well as
>> 1.0.29) but I also get a pile of multiple definitions for sanei_debug
>> and sanei_usb functions when linking libdll_preload.a.
>
> I also saw these  "multiple definition"  warnings,  but in my experience
> compiling other people's programs almost ever produces some warnings, so
> what the heck :-)

That may be fine for you but when you report an issue it's nice to
include this.  Most folks on the list are not psychic and I didn't
get a crystal ball from Santa Claus last year either ;-/

BTW, although they don't cover many build scenarios, our Debian CI
builds are free of compiler warnings and we make an active effort to
keep them that way via "All Warnings Are Really Errors" (AWARE).

>> ...
>> I don't know what is going on off the top of my head but suggest you
>> follow Bruce's suggestion, at least for the time being, unless you
>> really *need* the --disable-dynamic *and* --enable-preload options.
>
> I did, and yes, now the compilation succeedes.  I'll tackle the original
> problem with scanning using the ADF next  and will report here what I'll
> find out.

OK.

> Regarding all these options,  well "./configure help" could probably not
> be more nebulous:
>
>   --enable-static[=PKGS]  build static libraries [default=no]
>   --enable-shared[=PKGS]  build shared libraries [default=yes]

Those are courtesy of libtool, so you can blame its developers for that.

> # So why not specify "--enable-shared"?
>
>   ...
>   --disable-dynamic       Disable dynamic loading of backends

Dynamic loading and shared libraries are two different things.  Shared
libraries are automatically loaded at program startup.  As a programmer
you don't have to do anything to get that taken care of.  For dynamic
loading you actually have to write code that loads the library if your
program decides it's needed.  Our dll backend does dynamic loading and
is the default libsane shared library.

> # Since I'm only specifying a single backend anyway,  why not include it
> # right into the binary rather than load it at start-up?

Why not make that backend your libsane instance?  Then your SANE
frontend will load that automatically at program start up if it's
dynamically linked with the libsane shared library.

# You'd cut the dll backend out of the picture this way.

>   ...
>   --disable-preload       Disable preloading of backends

To be honest, I'm not sure what this option achieves myself.

> # As above: why not enable this option and thus include the single back-
> # end right into the binary?
>
> But obviously my interpretation of these option descriptions was bogus.

I hope the above clarified a bit but, when in doubt or not really
knowing what you're doing, going with the defaults is often not a
bad decision ;-)

> By the way: I'm meanwhile also specifying "--disable-locking" to get rid
> of this warning about allegedly missing group "uucp".

Hope this helps,
--
Olaf Meeuwissen, LPIC-2            FSF Associate Member since 2004-01-27
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