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authorJörg Frings-Fürst <debian@jff-webhosting.net>2014-10-06 14:00:40 +0200
committerJörg Frings-Fürst <debian@jff-webhosting.net>2014-10-06 14:00:40 +0200
commit6e9c41a892ed0e0da326e0278b3221ce3f5713b8 (patch)
tree2e301d871bbeeb44aa57ff9cc070fcf3be484487 /doc/backend-writing.txt
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+2006-01-01
+
+Here are a few rules and tips that should help writing a
+SANE-conforming backend and including it into the SANE package:
+
+
+GETTING STARTED
+---------------
+
+* You will need information about the protocol the scanner (or other image
+ application device) is using. The easiest way is to ask the manufacturer
+ about it. You should mention that the code will be open-source, however.
+
+* Read the SANE standard.
+
+* One approach is to write a stand-alone scanning program first. Debugging
+ this program is usually easier than using the SANE libraries. However, keep
+ in mind what you learned from the SANE standard.
+
+* Once your program works basically, insert its functions into a basically
+ empty SANE backend. You can get one by removing everything but the SANE
+ includes and SANE API function definitions from an existing backend (e.g.
+ test.c).
+
+* If you have any information about the scanner you want to support that
+ is not already mentioned in one of the .desc files, please contact the
+ sane-devel mailing list. Especially if you have written code (e.g. a test
+ program) or started writing a backend, contact us.
+
+* Keep other users informed about what you did and want to do. This way no
+ work is done twice and you may get volunteers for coding or testing.
+ Set up a website or at least write to sane-devel. If you have a website,
+ a link to it can be included in the .desc file and users looking for that
+ scanner will find it on the SANE website.
+
+* When you have a working backend but you don't want to have it included
+ in the SANE distribution yet, at least the .desc file can be included
+ (see below for details). So people will find a link to your backend at
+ the SANE webpage.
+
+
+CONFIGURATION AND BUILD SYSTEM
+------------------------------
+
+Sane-backends uses the autoconf and automake tools. The configure script is
+generated from configure.in and aclocal.m4 by running "autoreconf".
+Simple checks (e.g. for headers) should be placed into configure.in while
+for more complex stuff acinclude.m4 is the right file. After changes in one
+of these files, "autoreconf" should be called. This will then call a
+chain of autotools, such as autoconf to generate configure, autoheader
+to generate include/sane/config.h.in, and automake to generate various
+Makefile.in's from Makefile.am's. All changes made by "autoreconf" must
+be commited together.
+
+When running configure, the Makefiles in the main and sub-directories are
+created from their respective Makefile.in files. Also include/sane/config.h
+which is included into to every c file is created from its .in file.
+
+Running "make" runs the respective targets in the sub directories recursively.
+
+The Makefile.am in each directory contains lists of files which are part of the
+distribution and which are therefore copied to the tar.gz archive, when a
+release is made. It's important that newly added files are also added to
+a variable that will cause them to be distributed (EXTRA_DIST at a minimum).
+
+For creating binaries and libraries libtool is used. The ltmain.sh script
+contains special modifications for SANE. These modifications ensure that
+the soname of each SANE backend library is "libsane.so". Without this
+change, backend libraries (like "libsane-epson.so") could not used as
+on-the-fly replacement for the dll backend.
+
+DIRECTORY OVERVIEW
+------------------
+
+This chapter explains some details about the files and directories used in the
+sane-backends distribution.
+
+sane-backends/
+ * acinclude.m4 aclocal.m4 compile config.guess config.sub configure
+ configure.in depcomp install-sh ltmain.sh Makefile.am Makefile.in missing
+ mkinstalldirs: Part of the build system as explained above.
+ * ChangeLog:
+ The ChangeLog contains all the changes made since the last stable release.
+ If anything is changed in git, it must be also mentioned in ChangeLog.
+ It's not enough to write just a git commit message, as users won't have
+ access to these messages. For more details on the format, see the SANE
+ git page on the website.
+ * ChangeLog-1.0.0, ChangeLog-1.0.1 (...):
+ These files contain the ChangeLogs of older releases. Once a new release has
+ been made, the current ChangeLog renamed to ChangeLog-1.something.something
+ and a new empty ChangeLog is created.
+ * AUTHORS COPYING INSTALL LICENSE:
+ General documentation + license.
+ * NEWS:
+ This is some kind of executive summary of the ChangeLog. It will be created
+ before a release.
+ * PROBLEMS:
+ General (severe) problems that all SANE users should be
+ aware. Backend-specific trouble should normally not mentioned there.
+ * PROJECTS:
+ Planned SANE-related development (e.g. ports, frontends). New backends won't
+ be listed here but a new .desc file will be created for them (see below).
+ * README:
+ General building instructions.
+ * README.aix README.beos (...):
+ Platform-dependent building and usage instructions.
+ * sane-backends.lsm:
+ The .lsm file as used for the ibiblio archive.
+
+sane-backends/backend/
+ This is where the actual backend code is placed. As an example the file
+ structure for a backend named "newbackend" is listed below. Backend names must
+ be unique and should not contain any special characters. Lower case letters,
+ numbers and underscores "_" are ok.
+ Backend documentation of any kind should not be placed here but in the doc/
+ directory. Code which is useful for more than one backend should be placed in
+ sanei/ instead.
+ * newbackend.c:
+ The main backend file, usually contains the SANE API code. Mandatory.
+ * newbackend.h:
+ Header file, containing includes and so on.
+ * newbackend.conf.in:
+ Configuration file for the backend, newbackend.conf will be created by
+ running "make" from this file. Some variables are substituted, e.g. for
+ installation directories. This is especially useful for firmware
+ directories. See Makefile.am for a list.
+ * newbackend-low.c:
+ Contains low level code for the "newbackend" backend. Depending on the
+ complexity of the backend, splitting it to several files can be appropriate,
+ the total number of files shouldn't exceed approx. 10, however.
+ Other files:
+ * Makefile.am, Makefile.in:
+ Makefile.am contains rather complex rules for building the backends. For
+ adding backends, special care should be taken concerning the FIRMWARE_DIRS
+ (add your backend name here, if your scanner needs firmware files) and
+ other variables (see build system description). There is some
+ documentation inside of Makefile.am on what needs to be added and where.
+ At a minimum, a convenience library of form lib${backend}.la and
+ a installed library libsane-${backend}.la must be defined. Any
+ sanei objects referenced should be listed in a
+ libsane_${backend}_la_LIBADD line.
+ * sane_strstatus.c:
+ Contains the code for the sane_strstatus() function to avoid code
+ duplication in every backend.
+
+sane-backends/doc/
+ Documentation for SANE. For some more details, see chapter DOCUMENTATION
+ below. Again an example for "newbackend":
+ * sane-newbackend.man:
+ The manual page of the backend. From this file, "sane-newbackend.5" is
+ generated by running "make".
+ * newbackend/ (directory)
+ Contains additional information about newbackend, e.g. READMEs or TODO
+ files.
+ General files:
+ * Makefile.in:
+ "sane-newbackend.5" must be added to variable BACKEND_5MANS and
+ "sane-newbackend.man" to EXTRA_DIST. A backend documentation directory
+ (if used) must be added to the BEDOCS variable.
+ * backend-writing.txt:
+ This file.
+ * descriptions.txt:
+ Describes the format of .desc files.
+ * doxygen-sanei.conf.in:
+ Used by doxygen to create the documentation of the sanei code.
+ * releases.txt:
+ Explains how to make releases of sane-backends.
+ * sane.tex, net.tex:
+ Contains the LaTeX source of the SANE standard.
+ * descriptions/ (directory)
+ Contains the .desc files for every backend that is included into
+ sane-backends.
+ * descriptions-external/ (directory)
+ Contains the .desc files for backend that are not included into
+ sane-backends yet (external backends). These files should only be created
+ if the code it points to is really a SANE backend (and not just a command
+ line program).
+
+sane-backends/frontend/
+ Contains the frontends scanimage, saned, and tstbackend.
+
+sane-backends/include/
+ Header files used by the SANE backends. The main directory contains the
+ headers used for general librar functions like getopt, while the
+ SANE-specific headers are located in include/sane/:
+ * config.h.in:
+ Main header file needed for portablility. config.h is created from this
+ file and must be included by every backend.
+ * sane.h:
+ Official SANE API header file. Don't change this without discussion on
+ the sane-devel mailing list.
+ * saneopts.h:
+ Defines several option NAMEs, TITLEs and DESCs that are (or should be)
+ used by several backends.
+ * sanei_*:
+ Sanei (SANE internal) headers. Needed for code used in several backends
+ like USB access. For more details, see the documentaion on the SANE website.
+
+sane-backends/japi/
+ Contains Java interface for SANE. See README.JAVA for details.
+
+sane-backends/lib/
+ Contains various library functions that may miss in the standard C library
+ of some platforms.
+
+sane-backends/po/
+ Translations of SANEbackend options. See README for details.
+
+sane-backends/sanei/
+ Sanei (SANE internal) code. Needed for code used in several backends
+ like USB access. For more details, see the documentaion on the SANE
+ website.
+
+sane-backends/testsuite/
+ Testsuite for SANE. See README for details.
+
+sane-backends/tools/
+ Contains several tools for SANE. There are backend-specific and general command line
+ tools as well as the hotplug support and .desc file generation code. See
+ README for details.
+
+
+PROGRAMMING
+-----------
+
+* A backend library is always only one file (libsane-backendname.so). Please do
+ not use multiple libraries e.g. for lower and higher level code.
+
+* To add the backend to the existing SANE code, the following must be done at
+ least:
+ - add the backend name to ALL_BACKENDS in configure.in (and run autoreconf)
+ - Add new backend to BACKEND_CONFS, be_convenience_libs, be_dlopen_libs,
+ and define _lib${backend}_la_SOURCES and
+ nodist_libsane_${backend}_la_SOURCES; using an existing backend as
+ a template. Any sanei reference code should be listed in
+ libsane_${backend}_la_LIBADD as well as any external libraries
+ required to resolve all symbols.
+ - Add the source code files to the backend/ directories. All file names
+ must start with the backend name (e.g. newbackend.c, newbackend.h and
+ newbackend-usb.c).
+
+* Please follow the GNU coding standards. It's clear that the style
+ outlined there is nobody's favorite, but it's much easier to
+ maintain SANE if everybody follows more or less the same coding
+ style. It also looks more professional. The GNU standards can be
+ found at:
+
+ http://www.gnu.org/prep/standards_toc.html
+ ftp://ftp.gnu.org/pub/gnu/standards/standards.text
+
+ Note that GNU emacs supports automatic indentation according to this
+ standard. The command "indent -gnu" can be used to reformat
+ existing sources according to this standard.
+
+* Please be courteous to programmer's with terminals that are 80
+ characters wide. It's not difficult to avoid long lines, so please
+ do so. Note that in ANSI C you can split long strings into pieces
+ separated by white space. For example,
+ "this is an awfully long string" can be written as "this is an "
+ "awfully long string".
+
+* Use only ANSI C for your backend. C99 is not supported by the compilers of
+ some older platforms so please avoid using its features.
+
+* Please do not depend on compiler specific features or, if you do, make
+ the dependency conditional so other compilers will still be able to
+ compile the files. In particular:
+
+ - do not use C++ style comments (//-line comments)
+
+ - do not declare dynamically sized automatic arrays; instead,
+ use alloca() after including "../include/lalloca.h". For example:
+
+ void
+ func (int n)
+ {
+ char buf[n];
+ }
+
+ should be re-written as:
+
+ #ifdef _AIX
+ # include "../include/lalloca.h" /* MUST come first for AIX! */
+ #endif
+
+ #include "../include/sane/config.h"
+ #include "../include/lalloca.h"
+ :
+ void
+ func (int n)
+ {
+ char *buf = alloca (n);
+ }
+ - Don't use any #pragma directives---they're completely
+ compiler-dependent.
+
+* If you use headers or libraries that may not be available on all systems,
+ write a check for configure.in and include it conditionally. If your backend
+ depends on these libraries or headers, compile the backend only if they are
+ available (see pint for an example).
+
+* Use #include ".../include/sane/..." to include the sane header files
+ instead of #include <sane/...>. Otherwise problems with different installed
+ SANE versions may occur. Also this makes clear that the local files are used.
+
+* Don't forget to #include ".../include/sane/config.h" in your backend before
+ any other includes. This must be done for any .c file that generates its own
+ object file. If you use lalloca.h see above for the correct includes.
+
+* Include sanei_backend.h after the other includes.
+
+* It's no longer necessary to #define PATH_MAX (now in sanei_backend.h).
+ If you define it, do so *after* the system includes.
+
+* Please use sanei functions whenever possible (e.g.
+ sanei_config_read()). This makes porting to other os/platforms much
+ easier. Most of these functions are documented in their respective
+ header files in include/sane/sanei_*.h. For most of them there is also
+ documentation in doxygen format: http://www.sane-project.org/sanei/. These
+ HTML pages can be generated by calling "doxygen sanei-doxygen.conf" in
+ the doc/ directory.
+
+* Initialize global variables explicitly in sane_init. Keep in mind that
+ sane_init can be called more than once (if sane_exit is called everytime
+ after sane_init). Therefore don't depend on automatic initialization to
+ 0 / NULL.
+
+* Do make sure that your code is byte-order independent. This is
+ particularly important for networking-related code and when dealing
+ with non-textual data files.
+
+* Don't use printf, fprintf or perror to output debug or error messages.
+ Use the DBG macro instead. If your backend can't detect a scanner for
+ whatever reason it shouldn't output anything as long as
+ SANE_DEBUG_BACKENDNAME isn't set. So don't use DBG(0, ...) in this case.
+
+* Please do not assume that `size_t' is `unsigned int'. On some
+ systems, it's `unsigned long' and the size of this type may be
+ bigger than that of an int (this is true for practically any of the
+ 64-bit systems). To print a variable of type size_t portably, cast
+ the variable to u_long and print it with the %lu specifier. E.g.:
+
+ size_t len;
+
+ DBG(3, "len=%lu\n", (u_long) len);
+
+* Please do not assume that `void *' has the same size as `int'. On some
+ systems, it's `long' and the size of this type may be bigger than that of
+ an int (this is true for practically any of the 64-bit systems). Where this
+ comes up is with opaque handles. For example:
+
+ int OpaqueHandle;
+ MyScanner *s = (MyScanner *)OpaqueHandle;
+
+ will FAIL on most 64 bit systems. Please use `void *' or better
+ `SANE_Handle'.
+
+* Don't use exit() in your backend. You will exit the whole program, not only
+ your backend.
+
+* If you use wait() or waitpid() in your backend, check its return value. This
+ is important, if the status value is checked for e.g. WIFEXITED after the
+ call of wait() or waitpid(). Both functions may fail if the frontend already
+ did a wait for the children.
+
+* Please try to avoid compilation warnings. At least with "--disable-warnings"
+ there shouldn't be warnings when compiling backends. It's not necessary to
+ fix every "unused parameter" warning but take care that no warnings pointing
+ to really existing problems or ambiguities are missed. Some programming
+ techniques generating warnings on gcc may lead to errors on other systems.
+
+* To support translation of SANE options, please mark the descriptions (desc)
+ and title of options with SANE_I18N() and add all files using SANE_I18N() to
+ po/POTFILES. See po/README for details.
+
+* Please check for TL_X < BR_X and TL_Y < BR_Y to avoid segfaults or even
+ scanner damage. This should NOT be done in sane_control_option, it should
+ be possible to temporary set TL_X > BR_X or TL_ > BR, otherwise it is hard
+ for a frontend to set the correct values.
+
+
+TESTING
+-------
+
+* Please test a backend with "scanimage -T" (plus other options,
+ as appropriate/necessary) as this will make sure that sane_read()
+ always returns the correct amount of data etc.
+
+* You can also test a backend with tstbackend. tstbackend is not
+ compiled nor installed by default. To do that, cd into frontend and
+ run "make tstbackend".
+
+* Please test a backend not just with scanimage and xscanimage
+ (+ other frontends), but also with saned. Based on past experience,
+ it is often the case that remote scanning can uncover subtle bugs.
+ Note that you don't have to use two different machines to test "remote"
+ scanning---you can use one and the same machine to test a backend via saned
+ (just be sure to enable the "net" backend in dll.conf and follow the
+ steps described in saned(8)).
+
+* Please test on every available platform/os. Even if no scanner is attached
+ to this system, test compilation and running scanimage. If you don't have
+ access to other platforms, ask sane-devel.
+
+* Please make sure that all global symbols exported from a SANE backend start
+ with the prefix "sane" or "sanei" to avoid clashes with exported symbols
+ of other backends. Only symbols mentioned in the SANE standard should start
+ with "sane_*". Make sure, the sanei_* symbols are unique, e.g. by using
+ sanei_backendname_*. Only export symbols that are absolutely necessary.
+ You can verify this by running GNU "nm" on the static library. For example:
+
+ nm -g backend/.libs/libsane-hp.a
+
+ would list all global symbols in the HP backend.
+
+ "./configure; make; make libcheck" in the sane-backends root directory
+ will name all backend libraries, that contain "illegal" symbols.
+
+DOCUMENTATION
+-------------
+
+* Even if you haven't written a man-page for your backend yet, you *must*
+ create a .desc file which describes it. Anytime you submit source code for
+ your backend, you should include an update to the .desc file which reflects
+ the new state of the backend. The .desc files are used to create the HTML
+ lists of supported devices. These lists are updated automatically when you
+ change a .desc file in git. See e.g.
+ http://www.sane-project.org/lists/sane-mfgs-cvs.html for the results.
+
+* The .desc files are located in the directories "doc/descriptions" and
+ "doc/descriptions-external" (for included and external backends).
+
+* "doc/descriptions.txt" describes the format of the ".desc" files. There is
+ also a template for new .desc files: "template.desc.". The format of the
+ files in the two directories is very similar. If you'd like to try parsing
+ your creation to recreate the sane-backends webpages, cd into "tools/" and
+ enter "make sane-desc". You can either use sane-desc directly (try
+ "./sane-desc -h") or use "make html-pages" in "doc/".
+
+* For external backends, you don't need to supply :manpage and :version. The
+ manpage link won't work anyway and version will be outdated soon.
+
+* When your backend is included in the SANE distribution, add an entry to
+ doc/sane.man, AUTHORS and sane-backends.lsm. The sane.man entry should point
+ to your documentation (man-page, website, readme). Also move your .desc
+ file from "doc/descriptions-external" to "doc/descriptions" and update
+ them.
+
+* In your manual page (backend.man), use @LIBDIR@ and the other macros for
+ path names to the libraries, config files and documentation. Don't use fixed
+ paths as they will be wrong if SANE is installed with a different prefix
+ (e.g. /usr instead of /usr/local).
+
+* If you want to include READMEs, HTML files or other documentation, please
+ create your own directory (doc/backendname) and store your files in this
+ directory. If you only have a manual page a subdirectory isn't necessary.
+
+* Please keep your manpages and .desc files up-to-date especially regarding
+ version numbers.
+
+
+CHECKLIST: SUBMITTING A NEW BACKEND
+-----------------------------------
+
+In sane-backends/
+* Add the author(s) name(s) to AUTHORS
+* Correct any related entries in the bug-tracking system
+
+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 BACKEND_CONFS in Makefile.am
+
+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.
+
+In sane-backends/po/
+* Add all files using SANE_I18N() to po/POTFILES
+
+
+INCLUDING INTO git
+------------------
+
+* If you want to include your backend into SANE's git tree use the latest git
+ 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's git 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 git tree.