[sane-devel] sane_init(), sane_get_devices() and SANE_Authorization_Callback()

[m. allan noah]

2010/5/31 Kåre Särs <kare.sars at iki.fi>:
> On Thursday 27 May 2010 00:04:32 m. allan noah wrote:
>> >> Many backends do not properly re-scan for devices. Those backends
>> >> should be fixed. Which version of sane-backends is this?
>> >
>> > This was sane-backends 1.0.21 from the ubunntu ppa mentioned in a couple
>> > of mails back. The backends I use are epson2 and v4l
>>
>> v4l is pretty much unmaintained, so I don't know that will get fixed,
>> and A. Zummo has been too busy to work on epson2 lately, but I might
>> step in a fix that.
> Thanks.
>
> How big of a problem is this? I'm still thinking about calling an external
> application. Something like "scanimage -f %d;%v;%m;%t%n" just to get the
> updated list of available devices...
>
> Is that overkill? or is it bad because it would decrease the incentive to fix
> the real problem?
>
> Could it be seen as a security risk?
>
>> > One workaround I can think of would be to start a separate process that
>> > would read the available devices...
>>
>> only if you are going to use that process to also do the scanning,
>> since the device list would have to be rescanned in any other process.
>>
> I do not fully understand what you meant with this...

There is no guarantee that the names of the list of scanners will be
the same between processes. Also, if the original process has a
scanner open, it might not show up in the list provided by the new
process. All in all, it is a bad idea- dont do it.

>
>> >> > 4) Again in a multi threaded application there might be two scanners
>> >> > that require authentication. The resource string that is provided to
>> >> > SANE_Authorization_Callback() contains the backend name and a md5
>> >> > hash, but it does not contain the same ":libusb:001:004" extra info
>> >> > type of sting that sane_get_devices() returns for the backend.
>> >>
>> >> Which backend?
>> >
>> > At least "epson2" and "test" through the net backend.
>>
>> weird- i've never used the auth callback, and none of my backends need
>> it, so I'd have to play around with it to comment further...
>>
> I might have been a bit unclear :) just in case: I have authentication enabled
> for saned on the server. The syntax of the saned.users file indicates that
> saned only cares about the backend and not individual devices.

I have not investigated further, perhaps Julien has an idea.

allan
-- 
"The truth is an offense, but not a sin"