SANE working again - reason unknown, but udev from testing works

[Martin Pitt]

Hey Dirk,

keeping fullquote for the pkg-systemd mailing list if you don't mind,
to conclude the thread for the other readers.

Dirk Ritter [2015-07-08  3:39 +0200]:
> Everything seems fine on the udev side. Did test all the
> things you suggested with no permission change and hence
> no change on the SANE side whatsoever. Mock surprise!

Yay!

> Assuming it's just the permissions udev has to get right
> and nothing else, i.e. access for the scanner group.

That's right. SANE directly speaks to the raw USB device, udev isn't
involved in the actual communication.

> Heisenbugs lasting over a Weekend spent on SANE config
> debugging are rare, but it seems I just got one. At least
> there was no way to reproduce it. My guess would be that
> merely dropping back to the stable versions of SANE and
> udev and upgrading again from there back to testing might
> have done the trick. At least I continued with that right
> after giving up on the SANE config which - for all intends
> and purposes - seemed perfectly fine. I wasn't expecting
> that outcome, though. I was just hoping that older versions
> would simply continue to work as they used to for years.
> More likely it simply was the downgrade/upgrade cycle of
> SANE, BTW, but I'm rather clueless as to what actually
> might have gone wrong. (And I'm pretty certain that I didn't
> upgrade back to some later versions or whatever else would
> serve as a trivial explanation. Strange...)
> 
> Benefit: Disabling all SANE back-ends (besides the one I
> actually need) made SANE come up much faster, i.e. any
> front-end either fires up faster, or used to report that
> no devices could be found almost instantly - instead of
> taking a while to come up with that disappointing message.

I'm a bit confused now -- did you *just* downgrade/upgrade, or
additionally disabled some backends? In the latter case, the most
plausible explanation is that the newer version of sane comes with a
new driver which now tries to claim your scanner but doesn't work with
it. And the driver you selected now and used before does?

> Sorry for that, but at least it should be good News to
> you that everything seems to be fine on the udev side -
> after all.

Great, thanks for letting us know!

Martin
-- 
Martin Pitt                        | http://www.piware.de
Ubuntu Developer (www.ubuntu.com)  | Debian Developer  (www.debian.org)