Hi all, On 18.03.2008 16:03, m. allan noah wrote: > On Tue, Mar 18, 2008 at 10:24 AM, ?tienne Bersac <bersace03 at gmail.com> > wrote: >> Hi, >> >> In january 2007, happened a very good discussion this list about SANE >> and HAL wich led to shipping a basic fdi. >> >> http://lists.alioth.debian.org/pipermail/sane-devel/2007-January/018343.html. >> >> Currently, sane-desc generate a very basic fdi which only badge device >> as scanner and add a property "scanner.access_method" hardcoded to >> "proprietary", the latter is pretty useless ;) >> >> Please keep in mind that supporting HAL does NOT mean depending on HAL >> nor breaking API. >> >> >> Abel Deuring did a very nice job on sane-fdi, a parser for .desc file >> that provide much useful information right in the fdi. Sadly, the >> discussion stopped without a lot of success. I updated the sane-fdi >> script from Abel following the advice from Abel and Johannes Meixner. >> >> A device rule looks like : >> >> <device> >> <match key="usb.vendor_id" int="0x04a9"> >> <match key="usb.product_id" int="0x2207"> >> <append key="info.capabilities" type="strlist">scanner</append> >> <append key="scanner.api" type="strlist">sane</append> >> <append key="scanner.sane.model" type="strlist">Canon CanoScan >> N1220U</append> >> <append key="scanner.sane.backends" type="strlist">plustek</append> >> <append key="scanner.sane.backends.plustek.supportstatus" >> type="strlist">complete</append> >> <append key="scanner.sane.backends.plustek.comment" >> type="strlist">Identical to UMAX 3400</append> >> </match> >> </match> >> </device> >> >> The updated sane-fdi script is available at >> http://bersace03.free.fr/pub/Development/Scanner/sane-fdi . > > i've not looked at this code yet, but the output above seems reasonable. > >> There is still one thing needed to get full HAL support by SANE, build >> the SANE device name from those infos. >> >> One goal would be to allow frontend to provide an entry for each backend >> allowing user to select the backend to use. Using e.g. "Cannon CanoScan >> N1220U (complete support with plustek driver)" along "Canon CanoScan >> N1220U (complete support with umax driver)" will allow user to easily >> select driver. >> >> According to discussion about HAL and SANE last year, seems that the >> "udi:<backend>:<udi>" would be the solution for SANE to support HAL >> (without depending on it). See >> >> http://lists.alioth.debian.org/pipermail/sane-devel/2007-January/018353.html >> for details. > > ok, so lets assume that we have a new 'hal' meta backend to do some > 'magic'. when the dll backend is asked to open a device like > 'hal:<udi>:<backend>'. it will load the hal backend, and ask it to > open '<udi>:<backend>'. the hal backend will load '<backend>', and ask > it for a list of scanners it can find, and somehow pick the one that > goes with the '<udi>'. > > i am worried that the last step means that each backend will have to > know how to translate udi's.
As I understand it, the main point of the discussion is to find a way for HAL that allows "HAL aware applications" to access a specific scanner; this could be either a scan button daemon or a Sane frontend, or whatever else. HAL already has quite detailed knowledge about devices; what is missing is basically either a specialized "Sane-UDI" or another way to assign a "Sane device string" (like "fujitsu:libusb:005:003") to a specific device. HAL knows already quite many details about devices, like USB bus/devide numbers, SG device filenames and whatever else; the main problem is that the Sane device names do not give a reliable indicator, which device (in the HAL sense) belongs to a specific Sane device. Instead of making Sane "HAL-aware", we can also add a function like sane_get_device_information to the Sane API that would return data like USB bus and devices numbers, USB vendor/product IDs, the SCSI device filename, SCSI vendor/product strings, SCSI host/bus/device/LUN numbers similar things. A HAL callout (this is a script called by hald for certain devices either when the daemon starts or when a device has been hotplugged) can then call sane_get_devices, call sane_get_device_information for each Sane device and can this way decide, if a Sane device "matches" the "current" HAL device. And if the HAL and Sane devices match, the callout can add a property like scanner.sane.device_name to the HAL device, which would store the Sane device name as returned by sane_get_devices. This should be enough to allow "HAL aware" scan software to find and access devices via Sane. Abel PS: sorry, I don't have that much time to spare at present, so consider this more to be a "backseat driver" comment...