kopia lustrzana https://gitlab.com/sane-project/backends
494 wiersze
21 KiB
Plaintext
494 wiersze
21 KiB
Plaintext
2006-01-01
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Here are a few rules and tips that should help writing a
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SANE-conforming backend and including it into the SANE package:
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GETTING STARTED
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---------------
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* You will need information about the protocol the scanner (or other image
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application device) is using. The easiest way is to ask the manufacturer
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about it. You should mention that the code will be open-source, however.
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* Read the SANE standard.
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* One approach is to write a stand-alone scanning program first. Debugging
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this program is usually easier than using the SANE libraries. However, keep
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in mind what you learned from the SANE standard.
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* Once your program works basically, insert its functions into a basically
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empty SANE backend. You can get one by removing everything but the SANE
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includes and SANE API function definitions from an existing backend (e.g.
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test.c).
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* If you have any information about the scanner you want to support that
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is not already mentioned in one of the .desc files, please contact the
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sane-devel mailing list. Especially if you have written code (e.g. a test
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program) or started writing a backend, contact us.
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* Keep other users informed about what you did and want to do. This way no
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work is done twice and you may get volunteers for coding or testing.
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Set up a website or at least write to sane-devel. If you have a website,
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a link to it can be included in the .desc file and users looking for that
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scanner will find it on the SANE website.
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* When you have a working backend but you don't want to have it included
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in the SANE distribution yet, at least the .desc file can be included
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(see below for details). So people will find a link to your backend at
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the SANE webpage.
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CONFIGURATION AND BUILD SYSTEM
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------------------------------
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Sane-backends uses the autoconf tools but not automake. The configure script is
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generated from configure.in and aclocal.m4 by running "autoconf". Simple checks
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(e.g. for headers) should be placed into configure.in while for more complex
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stuff acinclude.m4 is the right file. After changes in one of these files
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"autoheader" and "autoconf" should be called. Autoheader creates
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include/sane/config.h.in, while autoconf createts the "configure" script. In
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CVS, all these changes must be commited (configure.in, configure, acinclude.m4,
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include/sane/config.h.in).
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When running configure, the Makefiles in the main and sub-directories are
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created from their respective Makefile.in files. Also include/sane/config.h
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which is included into to every c file is created from its .in file.
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Running "make" runs the respective targets in the sub directories recursively.
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The Makefile.in in each directory contains lists of files which are part of the
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distribution and which are therefore copied to the tar.gz archive, when a
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release is made. It's important that newly added files are also added to their
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respective DISTFILES variables in the Makefile.in.
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For creating binaries and libraries libtool is used. The ltmain.sh script
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contains special modifications for SANE. In addition to fixes for MacOS these
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modifications ensure that the soname of each SANE backend library is
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"libsane.so". Without this change, backend libraries (like "libsane-epson.so")
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could not used as on-the-fly replacement for the dll backend.
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DIRECTORY OVERVIEW
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------------------
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This chapter explains some details about the files and directories used in the
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sane-backends distribution.
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sane-backends/
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* acinclude.m4 aclocal.m4 config.guess config.sub configure configure.in
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install-sh ltmain.sh Makefile.in mkinstalldirs:
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Part of the build system as explained above.
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* ChangeLog:
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The ChangeLog contains all the changes made since the last stable release. If
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anything is changed in CVS, it must be also mentioned in ChangeLog. It's not
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enough to write just a CVS commit message, as users won't have access to
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these messages. For more details on the format, see the SANE CVS page on the
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website.
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* ChangeLog-1.0.0, ChangeLog-1.0.1 (...):
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These files contain the ChangeLogs of older releases. Once a new release has
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been made, the current ChangeLog renamed to ChangeLog-1.something.something
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and a new empty ChangeLog is created.
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* AUTHORS COPYING LICENSE:
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General documentation + license.
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* NEWS:
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This is some kind of executive summary of the ChangeLog. It will be created
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before a release.
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* PROBLEMS:
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General (severe) problems that all SANE users should be
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aware. Backend-specific trouble should normally not mentioned there.
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* PROJECTS:
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Planned SANE-related development (e.g. ports, frontends). New backends won't
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be listed here but a new .desc file will be created for them (see below).
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* README:
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General building instructions.
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* README.aix README.beos (...):
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Platform-dependent building and usage instructions.
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* sane-backends.lsm:
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The .lsm file as used for the ibiblio archive.
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sane-backends/backend/
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This is where the actual backend code is placed. As an example the file
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structure for a backend named "newbackend" is listed below. Backend names must
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be unique and should not contain any special characters. Lower case letters,
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numbers and underscores "_" are ok.
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Backend documentation of any kind should not be placed here but in the doc/
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directory. Code which is useful for more than one backend should be placed in
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sanei/ instead.
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* newbackend.c:
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The main backend file, usually contains the SANE API code. Mandatory.
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* newbackend.h:
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Header file, containing includes and so on.
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* newbackend.conf.in:
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Configuration file for the backend, newbackend.conf will be created by running
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"make" from this file. Some variables are substituted, e.g. for installation
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directories. This is especially usefukl for frimware directories. See
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Makefile.in for a list.
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* newbackend-low.c:
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Contains low level code for the "newbackend" backend. Depending on the
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complexity of the backend, splitting it toseveral files can be appropriate,
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the total number of files shouldn't exceed approx. 10, however.
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Other files:
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* Makefile.in:
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Makefile.in contains rather complex rules for building the backends. For
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adding backends, special care should be taken concerning the FIRMWARE_DIRS
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(add your backend name here, if your scanner needs firmware files) and
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DISTFILES variables (see build system description). If your backend uses
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separate object files, the additional dependencies must be added to the
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EXTRA_newbackend variable. Also each backend that uses code from sanei must add
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a line for each sanei file used, for sanei_usb code:
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libsane-newbackend.la: ../sanei/sanei_usb.lo
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* sane_strstatus.c:
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Contains the code for the sane_strstatus() function to avoid code
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duplication in every backend.
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sane-backends/doc/
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Documentation for SANE. For some more details, see chapter DOCUMENTATION
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below. Again an example for "newbackend":
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* sane-newbackend.man:
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The manual page of the backend. From this file, "sane-newbackend.5" is
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generated by running "make".
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* newbackend/ (directory)
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Contains additional information about newbackend, e.g. READMEs or TODO
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files.
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General files:
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* Makefile.in:
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"sane-newbackend.5" must be added to variable SECT5 and
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"sane-newbackend.man" to DISTFILES. A backend documentation directory (if
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used) must be added to the BACKDIRS variable.
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* backend-writing.txt:
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This file.
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* descriptions.txt:
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Describes the format of .desc files.
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* doxygen-sanei.conf.in:
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Used by doxygen to create the documentation of the sanei code.
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* releases.txt:
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Explains how to make releases of sane-backends.
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* sane.tex, net.tex:
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Contains the LaTeX source of the SANE standard.
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* descriptions/ (directory)
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Contains the .desc files for every backend that is included into sane-backends.
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* descriptions-external/ (directory)
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Contains the .desc files for backend that are not included into
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sane-backends yet (external backends). These files should only be created
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if the code it points to is really a SANE backend (and not just a command
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line program).
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sane-backends/frontend/
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Contains the frontends scanimage, saned, and tstbackend.
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sane-backends/include/
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Header files used by the SANE backends. The main directory contains the
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headers used for general librar functions like getopt, while the
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SANE-specific headers are located in include/sane/:
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* config.h.in:
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Main header file needed for portablility. config.h is created from this
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file and must be included by every backend.
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* sane.h:
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Official SANE API header file. Don't change this without discussion on
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the sane-devel mailing list.
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* saneopts.h:
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Defines several option NAMEs, TITLEs and DESCs that are (or should be)
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used by several backends.
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* sanei_*:
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Sanei (SANE internal) headers. Needed for code used in several backends
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like USB access. For more details, see the documentaion on the SANE website.
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sane-backends/japi/
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Contains Java interface for SANE. See README.JAVA for details.
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sane-backends/lib/
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Contains various library functions that may miss in the standard C library
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of some platforms.
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sane-backends/po/
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Translations of SANEbackend options. See README for details.
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sane-backends/sanei/
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Sanei (SANE internal) code. Needed for code used in several backends
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like USB access. For more details, see the documentaion on the SANE website.
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sane-backends/testsuite/
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Testsuite for SANE. See README for details.
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sane-backends/tools/
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Contains several tools for SANE. There are backend-specific and general command line
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tools as well as the hotplug support and .desc file generation code. See
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README for details.
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PROGRAMMING
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-----------
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* A backend library is always only one file (libsane-backendname.so). Please do
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not use miltiple libraries e.g. for lower and higher level code.
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* To add the backend to the existing SANE code, the following must be done at
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least:
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- add the backend name to BACKENDS in configure.in (and rerun autoconf)
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- add any parts of SANE that are used in the backend in
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backend/Makefile.in. E.g., for the backend "newbackend" that uses
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sanei_usb code:
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libsane-newbackend.la: ../sanei/sanei_usb.lo
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See the lines near the end of Makefile.in for examples.
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- Add the source code files to the backend/ directories. All file names must
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start with the backend name (e.g. newbackend.c, newbackend.h and
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newbackend-usb.c).
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* Please follow the GNU coding standards. It's clear that the style
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outlined there is nobody's favorite, but it's much easier to
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maintain SANE if everybody follows more or less the same coding
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style. It also looks more professional. The GNU standards can be
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found at:
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http://www.gnu.org/prep/standards_toc.html
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ftp://ftp.gnu.org/pub/gnu/standards/standards.text
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Note that GNU emacs supports automatic indentation according to this
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standard. The command "indent -gnu" can be used to reformat
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existing sources according to this standard.
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* Please be courteous to programmer's with terminals that are 80
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characters wide. It's not difficult to avoid long lines, so please
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do so. Note that in ANSI C you can split long strings into pieces
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separated by white space. For example,
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"this is an awfully long string" can be written as "this is an "
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"awfully long string".
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* Use only ANSI C for your backend. C99 is not supported by the compilers of
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some older platforms so please avoid using its features.
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* Please do not depend on compiler specific features or, if you do, make
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the dependency conditional so other compilers will still be able to
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compile the files. In particular:
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- do not use C++ style comments (//-line comments)
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- do not declare dynamically sized automatic arrays; instead,
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use alloca() after including "../include/lalloca.h". For example:
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void
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func (int n)
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{
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char buf[n];
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}
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should be re-written as:
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#ifdef _AIX
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# include "../include/lalloca.h" /* MUST come first for AIX! */
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#endif
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#include "../include/sane/config.h"
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#include "../include/lalloca.h"
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:
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void
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func (int n)
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{
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char *buf = alloca (n);
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}
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- Don't use any #pragma directives---they're completely
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compiler-dependent.
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* If you use headers or libraries that may not be available on all systems,
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write a check for configure.in and include it conditionally. If your backend
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depends on these libraries or headers, compile the backend only if they are
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available (see pint for an example).
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* Use #include ".../include/sane/..." to include the sane header files
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instead of #include <sane/...>. Otherwise problems with different installed
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SANE versions may occur. Also this makes clear that the local files are used.
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* Don't forget to #include ".../include/sane/config.h" in your backend before
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any other includes. This must be done for any .c file that generates its own
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object file. If you use lalloca.h see above for the correct includes.
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* Include sanei_backend.h after the other includes.
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* It's no longer necessary to #define PATH_MAX (now in sanei_backend.h).
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If you define it, do so *after* the system includes.
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* Please use sanei functions whenever possible (e.g.
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sanei_config_read()). This makes porting to other os/platforms much
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easier. Most of these functions are documented in their respective
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header files in include/sane/sanei_*.h. For most of them there is also
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documentation in doxygen format: http://www.sane-project.org/sanei/. These
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HTML pages can be generated by calling "doxygen sanei-doxygen.conf" in
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the doc/ directory.
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* Initialize global variables explicitly in sane_init. Keep in mind that
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sane_init can be called more than once (if sane_exit is called everytime
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after sane_init). Therefore don't depend on automatic initialization to
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0 / NULL.
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* Do make sure that your code is byte-order independent. This is
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particularly important for networking-related code and when dealing
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with non-textual data files.
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* Don't use printf, fprintf or perror to output debug or error messages.
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Use the DBG macro instead. If your backend can't detect a scanner for
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whatever reason it shouldn't output anything as long as
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SANE_DEBUG_BACKENDNAME isn't set. So don't use DBG(0, ...) in this case.
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* Please do not assume that `size_t' is `unsigned int'. On some
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systems, it's `unsigned long' and the size of this type may be
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bigger than that of an int (this is true for practically any of the
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64-bit systems). To print a variable of type size_t portably, cast
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the variable to u_long and print it with the %lu specifier. E.g.:
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size_t len;
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DBG(3, "len=%lu\n", (u_long) len);
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* Please do not assume that `void *' has the same size as `int'. On some
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systems, it's `long' and the size of this type may be bigger than that of
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an int (this is true for practically any of the 64-bit systems). Where this
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comes up is with opaque handles. For example:
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int OpaqueHandle;
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MyScanner *s = (MyScanner *)OpaqueHandle;
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will FAIL on most 64 bit systems. Please use `void *' or better
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`SANE_Handle'.
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* Don't use exit() in your backend. You will exit the whole program, not only
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your backend.
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* If you use wait() or waitpid() in your backend, check its return value. This
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is important, if the status value is checked for e.g. WIFEXITED after the
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call of wait() or waitpid(). Both functions may fail if the frontend already
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did a wait for the children.
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* Please try to avoid compilation warnings. At least with "--disable-warnings"
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there shouldn't be warnings when compiling backends. It's not necessary to
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fix every "unused parameter" warning but take care that no warnings pointing
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to really existing problems or ambiguities are missed. Some programming
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techniques generating warnings on gcc may lead to errors on other systems.
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* To support translation of SANE options, please mark the descriptions (desc)
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and title of options with SANE_I18N(). See po/README for details.
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* Please check for TL_X < BR_X and TL_Y < BR_Y to avoid segfaults or even
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scanner damage. This should NOT be done in sane_control_option, it should
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be possible to temporary set TL_X > BR_X or TL_ > BR, otherwise it is hard
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for a frontend to set the correct values.
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TESTING
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-------
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* Please test a backend with "scanimage -T" (plus other options,
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as appropriate/necessary) as this will make sure that sane_read()
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always returns the correct amount of data etc.
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* You can also test a backend with tstbackend. tstbackend is not
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compiled nor installed by default. To do that, cd into frontend and
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run "make tstbackend".
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* Please test a backend not just with scanimage and xscanimage
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(+ other frontends), but also with saned. Based on past experience,
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it is often the case that remote scanning can uncover subtle bugs.
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Note that you don't have to use two different machines to test "remote"
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scanning---you can use one and the same machine to test a backend via saned
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(just be sure to enable the "net" backend in dll.conf and follow the
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steps described in saned(8)).
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* Please test on every available platform/os. Even if no scanner is attached
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to this system, test compilation and running scanimage. If you don't have
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access to other platforms, ask sane-devel.
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* Please make sure that all global symbols exported from a SANE backend start
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with the prefix "sane" or "sanei" to avoid clashes with exported symbols
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of other backends. Only symbols mentioned in the SANE standard should start
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with "sane_*". Make sure, the sanei_* symbols are unique, e.g. by using
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sanei_backendname_*. Only export symbols that are absolutely necessary.
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You can verify this by running GNU "nm" on the static library. For example:
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nm -g backend/.libs/libsane-hp.a
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would list all global symbols in the HP backend.
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"./configure --disable-shared; make; make libcheck" in the sane-backends
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root directory will name all backend libraries, that contain "illegal"
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symbols.
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DOCUMENTATION
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-------------
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* Even if you haven't written a man-page for your backend yet, you *must*
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create a .desc file which describes it. Anytime you submit source code for
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your backend, you should include an update to the .desc file which reflects
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the new state of the backend. The .desc files are used to create the HTML
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lists of supported devices. These lists are updated automatically when you
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change a .desc file in CVS. See e.g.
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http://www.sane-project.org/lists/sane-mfgs-cvs.html for the results.
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* The .desc files are located in the directories "doc/descriptions" and
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"doc/descriptions-external" (for included and external backends).
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* "doc/descriptions.txt" describes the format of the ".desc" files. There is
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also a template for new .desc files: "template.desc.". The format of the
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files in the two directories is very similar. If you'd like to try parsing
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your creation to recreate the sane-backends webpages, cd into "tools/" and
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enter "make sane-desc". You can either use sane-desc directly (try
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"./sane-desc -h") or use "make html-pages" in "doc/".
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* For external backends, you don't need to supply :manpage and :version. The
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manpage link won't work anyway and version will be outdated soon.
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* When your backend is included in the SANE distribution, add an entry to
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doc/sane.man, AUTHORS and sane-backends.lsm. The sane.man entry should point
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to your documentation (man-page, website, readme). Also move your .desc
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file from "doc/descriptions-external" to "doc/descriptions" and update
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them.
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* In your manual page (backend.man), use @LIBDIR@ and the other macros for
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path names to the libraries, config files and documentation. Don't use fixed
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paths as they will be wrong if SANE is installed with a different prefix
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(e.g. /usr instead of /usr/local).
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* If you want to include READMEs, HTML files or other documentation, please
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|
create your own directory (doc/backendname) and store your files in this
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|
directory. If you only have a manual page a subdirectory isn't necessary.
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|
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* Please keep your manpages and .desc files up-to-date especially regarding
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|
version numbers.
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|
|
|
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|
CHECKLIST: SUBMITTING A NEW BACKEND
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|
-----------------------------------
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|
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|
In sane-backends/
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|
* Add the author(s) name(s) to AUTHORS
|
|
* Correct any related entries in the bug-tracking system
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|
|
|
In sane-backends/backend/
|
|
* Use the command "indent -gnu" to reformat your code according to the
|
|
standard.
|
|
* Add the backend name to dll.conf
|
|
* Check that the SANE license is in the backend source files.
|
|
* Add the source file names and the .conf file
|
|
to DISTFILES in Makefile.in
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|
|
|
In sane-backends/doc/
|
|
* Add an entry for the man page in sane.man
|
|
* Add the man page file in doc/Makefile.in
|
|
* Move the description file from descriptions-external/ to doc/descriptions/
|
|
* Check that the description file is correct: "cd doc; make html-pages" and
|
|
check the html pages result with a browser.
|
|
* Check that the backend version is the same in the source and in the
|
|
description file.
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|
|
|
|
|
INCLUDING INTO CVS
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|
------------------
|
|
|
|
* If you want to include your backend into CVS use the latest CVS to make
|
|
patches. Check the mailing list and the bug-tracking system for information
|
|
about bugs to avoid.
|
|
|
|
* If your backend isn't included yet in the SANE CVS tree, write an email to
|
|
the SANE mailing list (sane-devel) and ask for inclusion. Usually one
|
|
of the developers will check the backend for common mistakes and test
|
|
compilation. If everything is ok the backend will be added to the CVS tree.
|