[sane-devel] Setting backend capabilities

Olaf Meeuwissen paddy-hack at member.fsf.org
Sun Mar 8 08:28:18 GMT 2020

Hi Ralph,

Ralph Little writes:

> Hi,
> On 2020-03-07 6:06 p.m., Olaf Meeuwissen wrote:
>> [...], I also think SANE_CAP_SOFT_SELECT is the better choice from
>> the user point of view.  However, you might consider adding a check for
>> the current hardware side setting to sane_control_option() so it can
>> signal the frontend in case changes were made hardware side.
>> # I considered adding a polling loop but that doesn't make much sense.
>> # You can only signal the frontend via sane_control_option() that it
>> # needs to SANE_INFO_RELOAD_OPTIONS, so checking there is good enough.
> Ah, I have implemented and checked in the change to make those sensors
> work but as you say, xsane currently does not take account of changes
> made on the hardware which is a shame.

As mentioned in my other reply, it is a limitation of the SANE API :-/

> I will look into the SANE_INFO_RELOAD_OPTIONS aspect.

And I only mentioned that as the best work-around I could think of
within the confines of the current SANE API (version 1.x).

> I think most proprietary scan software implementations that I have
> observed use a polling loop of some sort, some utilizing USB INTERRUPT,
> some not.

Making it clear that this needs to be absorbed by the backend so
frontends will not have to deal with this.

Fun point to consider: It has to work over the network protocol[2] as
well :-?

 [2]: https://sane-project.gitlab.io/standard/net.html

> When I have looked into that, perhaps you would be kind enough to
> review the changes? :D

Sure but anything that goes around version 1.x of the SANE API is a

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