NAME

       sane-dll - SANE dynamic backend loader

DESCRIPTION

       The  sane-dll  library  implements  a SANE (Scanner Access Now Easy) backend that provides
       access to an arbitrary number of other SANE backends.  These backends may either  be  pre-
       loaded  at  the  time  the  sane-dll  library 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 relevant library in
       /usr/lib/x86_64-linux-gnu/sane and adding an entry to the dll.conf configuration file.  In
       other  words,  no  applications  need  to be modified 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 everything 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 /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 /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 backend 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_BACKENDS  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 entries 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 accessed if the device name is known, it just doesn't appear
       on the list.

FILES

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

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

       /usr/lib/x86_64-linux-gnu/sane/libsane-dll.a
              The static library implementing this backend.

       /usr/lib/x86_64-linux-gnu/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.  On *NIX systems, the directories  are  separated  by  a  colon
              (`:'),  under  OS/2, they are separated by a semi-colon (`;').  If this variable is
              not set, the configuration file is searched in two default directories: first,  the
              current  working  directory  (".")  and  then  in /etc/sane.d.  If the value of the
              environment variable ends with the directory separator character, then the  default
              directories  are searched after the explicitly specified directories.  For example,
              setting SANE_CONFIG_DIR to "/tmp/config:" would result in  directories  tmp/config,
              ., and /etc/sane.d being searched (in this order).

       SANE_DEBUG_DLL
              If  the  library was compiled with debug support enabled, this environment 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)