[sane-devel] Sane Release 1.1.0 ?

[Johannes Meixner]

Hello,

On Nov 8 10:06 stef wrote (shortened):
> as a proof of concept,  I have made 2 different versions of SANE
> coexisting on my system.
...
> I have created a meta backend which is a copy of dll.c,
> but that searches only backends with a major of 1 and has no
> preloaded backends. I added the meta backend to dll.conf.

Very many thanks for this real test!

Regardless what the final result will be, the only thing which
is of real importance for us (i.e. for the openSUSE distribution)
is that different SANE versions work o.k. out of the box.

"work o.k. out of the box" means on the one hand
no loss of supported models (i.e. no regression bugs)
but on the other hand it menas that it can happily crash
when the user did special manual changes.

For example we use a backend only via a dll meta backend
(and I assume the other distribution do it too - i.e.
no backend is directly linked with a frontend) so that
you can add as many meta-backends as you like
as long as this works o.k. out of the box.

"Out of the box" means also that it would be no problem for us,
to provide an updated SANE 1 sane-backends package together
with a new SANE 2 sane2-backends package if changes in the
SANE 1 sane-backends package are required so that this one
can coexist with the SANE 2 sane2-backends package.
This is no problem for us because we provide the "whole box"
i.e. we can easily provide an updated SANE 1 sane-backends
package in the next openSUSE version if it is needed.
This would also work for an update from one openSUSE version
to the next openSUSE version because the installed packages
(i.e. the installed sane-backends) would be updated too.


If I understand you correctly, the dll meta backend
is the one of the newest SANE version.

Assume now there is SANE version 1, 2, and 3 which should
coexist on one system:

Then the dll meta backend is of version 3 which loads only
backends which are compatible with version 3 (i.e. in its
dll.conf there are only backends listed which are compatible
with version 3).

For backward compatibility with version 2, there is a dll2
meta-meta backend which is compatible with version 3
(i.e. listed in dll.conf) but this one loads only backends
which are not compatible with version 3 but which are
compatible with version 2 (i.e. in its dll2.conf there are
only backends listed which are compatible with version 2).

For backward compatibility with version 1, there is
either
a dll1 meta-meta backend which is compatible with version 3
(i.e. listed in dll.conf) but this one loads only backends
which are neither compatible with version 3 or version 2
but which are compatible with version 1 (i.e. in its dll1.conf
there are only backends which are compatible with version 1)
or
a dll1 meta-meta-meta backend which is compatible with version 2
(i.e. listed in dll2.conf) but this one loads only backends
which are not compatible with 2 but which are compatible
with version 1 (i.e. in its dll1.conf there are only backends
which are compatible with version 1)


Currently I do not fully understand all implications of it
but it seems that this naming scheme could be a drawback
because currently the dll meta backend is of version 1.

Why not keep the old name dll for the meta backend for version 1
and use new names (i.e. dll2 and dll3) for the higher versions?

Or is it better to overwrite an existing SANE version 1 dll
by the new dll and add dll2 for backward compatibility?


Kind Regards
Johannes Meixner
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