sane-dll.5



sane-dll(5)              SANE Scanner Access Now Easy              sane-dll(5)


NAME

       sane-dll - SANE dynamic backend loader


DESCRIPTION

       The  sane-dll library implements a SANE (Scanner Access Now Easy) back-
       end that provides access to an arbitrary number of other SANE backends.
       These  backends  may  either be pre-loaded at the time the sane-dll li-
       brary is built or, on systems that support dynamic  loading  of  shared
       libraries,  the backends may be loaded at runtime.  In the latter case,
       adding support for a new backend simply involves installing  the  rele-
       vant library in /usr/local/lib/sane and adding an entry to the dll.conf
       configuration file.  In other words, no applications need to  be  modi-
       fied or recompiled to add support for new devices.


DEVICE NAMES

       This backend expects device names of the form:

              backend:device

       Where  backend is the name of the backend and device is the name of the
       device in this backend that should be addressed.  If  the  device  name
       does  not contain a colon (:), then the entire string is treated as the
       device string for the default backend.   The  default  backend  is  the
       backend  listed last in the configuration file (see below) or the first
       pre-loaded backend (if any).


CONFIGURATION

       The contents of the dll.conf file is a list of backend names  that  may
       be  loaded  dynamically upon demand.  Empty lines are ignored, also ev-
       erything after a hash mark (#). A sample configuration  file  is  shown
       below:

              net
              # this is a comment
              pnm
              mustek

       It  is  also possible to add a file in /usr/local/etc/sane.d/dll.d that
       contains the list of backends to be added. Backends mentioned in a file
       included  in this directory will be added before any backends listed in
       dll.conf.  Files in /usr/local/etc/sane.d/dll.d can  be  freely  named.
       They shall follow the format conventions as apply for dll.conf.

       Note  that  backends that were pre-loaded when building this library do
       not have to be listed in this configuration file.  That is, if a  back-
       end was preloaded, then that backend will always be present, regardless
       of whether it's listed in the configuration file or not.

       The list of preloaded backends is determined by macro PRELOADABLE_BACK-
       ENDS  in file backend/Makefile.in of the SANE source code distribution.
       After changing the value of this macro, it is necessary to reconfigure,
       rebuild, and reinstall SANE for the change to take effect.

       Aliases are defined in the config file dll.aliases.  It can contain en-
       tries of the form

              alias SomeName SaneDeviceName
              alias "Some Name" SaneDeviceName
              hide SaneDeviceName

       For example:

              alias Epson net:somehost:epson:/dev/sgX
              alias "Siemens ST400" st400:/dev/sgY
              hide net:somehost:pnm:0
              hide net:somehost:pnm:1
              alias "Read from file" pnm:0
              hide pnm:1

       Aliased device names are automatically hidden.

       The idea is that users don't have to deal with complicated device names
       (especially  for networked devices), and to hide other exported devices
       which might confuse them. Note that a hidden device can  still  be  ac-
       cessed if the device name is known, it just doesn't appear on the list.


FILES

       /usr/local/etc/sane.d/dll.aliases
              The list of aliased or hidden backends.

       /usr/local/etc/sane.d/dll.conf
              The   backend   configuration  file  (see  also  description  of
              SANE_CONFIG_DIR below).

       /usr/local/lib/sane/libsane-dll.a
              The static library implementing this backend.

       /usr/local/lib/sane/libsane-dll.so
              The shared library implementing this backend (present on systems
              that support dynamic loading).


ENVIRONMENT

       SANE_CONFIG_DIR
              This environment variable specifies the list of directories that
              may contain the configuration file.  Under UNIX, the directories
              are  separated  by a colon (`:'), under OS/2, they are separated
              by a semi-colon (`;').  If this variable is not set, the config-
              uration  file is searched in two default directories: first, the
              current  working  directory   (".")   and   then   in   /usr/lo-
              cal/etc/sane.d.   If  the value of the environment variable ends
              with the directory separator character, then the default  direc-
              tories  are searched after the explicitly specified directories.
              For example, setting SANE_CONFIG_DIR to "/tmp/config:" would re-
              sult   in   directories   "tmp/config",   ".",   and   "/usr/lo-
              cal/etc/sane.d" being searched (in this order).

       SANE_DEBUG_DLL
              If the library was compiled with debug support enabled, this en-
              vironment  variable  controls  the debug level for this backend.
              E.g., a value of 128 requests all debug output  to  be  printed.
              Smaller levels reduce verbosity.

              Value  Description
              0      print severe errors only
              1      print normal errors and important messages
              2      print normal messages
              3      print debugging messages
              4      print everything

              Example: export SANE_DEBUG_DLL=3


SEE ALSO

       sane(7), scanimage(1), sane-"backendname"(5)


AUTHOR

       David Mosberger

                                  13 Jul 2008                      sane-dll(5)

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