Commit 22cbe825 authored by Paul Eggert's avatar Paul Eggert
Browse files

doc: move README into manual

* README: Move contents to new file doc/gnulib-readme.texi.
Replace with a one-line summary.
* doc/gnulib.texi (Brief Overview): New section,
with old intro preface.  Include gnulib-readme.texi for contents.
(Philosophy): Rename from "Introduction", since this
section no longer introduces the rest.  Write a new preface.
* doc/gnulib-readme.texi: New file, with the old contents of
README texinfo-ized.  This way, the README info appears
in the online and printed manual.
parent fc102289
2012-12-27 Paul Eggert <eggert@cs.ucla.edu>
doc: move README into manual
* README: Move contents to new file doc/gnulib-readme.texi.
Replace with a one-line summary.
* doc/gnulib.texi (Brief Overview): New section,
with old intro preface. Include gnulib-readme.texi for contents.
(Philosophy): Rename from "Introduction", since this
section no longer introduces the rest. Write a new preface.
* doc/gnulib-readme.texi: New file, with the old contents of
README texinfo-ized. This way, the README info appears
in the online and printed manual.
2012-12-25 Ben Pfaff <blp@cs.stanford.edu>
 
c-xvasprintf: Fix "implicit declaration of function" GCC warning.
Gnulib
======
While portability across operating systems is not one of GNU's primary
goals, it has helped introduce many people to the GNU system, and is
worthwhile when it can be achieved at a low cost. This collection helps
lower that cost.
Gnulib is intended to be the canonical source for most of the important
"portability" and/or common files for GNU projects. These are files
intended to be shared at the source level; Gnulib is not a typical
library meant to be installed and linked against. Thus, unlike most
projects, Gnulib does not normally generate a source tarball
distribution; instead, developers grab modules directly from the
source repository.
The easiest, and recommended, way to do this is to use the gnulib-tool
script. Since there is no installation procedure for Gnulib,
gnulib-tool needs to be run directly in the directory that contains the
Gnulib source code. You can do this either by specifying the absolute
filename of gnulib-tool, or by using a symbolic link from a
place inside your PATH to the gnulib-tool file of your preferred
Gnulib checkout. For example:
$ ln -s $HOME/gnu/src/gnulib.git/gnulib-tool $HOME/bin/gnulib-tool
The home page for Gnulib is http://www.gnu.org/software/gnulib.
git and CVS
===========
Gnulib is available for anonymous checkout. In any Bourne-shell the
following should work:
$ git clone git://git.sv.gnu.org/gnulib.git
For a read-write checkout you need to have a login on savannah.gnu.org and be
a member of the gnulib project at http://savannah.gnu.org/projects/gnulib .
Then, instead of the URL
git://git.sv.gnu.org/gnulib
use the URL
ssh://<user>@git.sv.gnu.org/srv/git/gnulib
where <user> is your login name on savannah.gnu.org.
git resources:
Overview: http://en.wikipedia.org/wiki/Git_(software)
Homepage: http://git.or.cz/
Download: http://www.kernel.org/pub/software/scm/git/
Tutorial: http://git.or.cz/course/
http://www.kernel.org/pub/software/scm/git/docs/tutorial.html
FAQ: http://git.or.cz/gitwiki/GitFaq
When you use "git annotate" or "git blame" with gnulib, it's recommended that
you use the "-w" option, in order to ignore massive whitespace changes that
happened in 2009.
CVS checkouts are also supported:
$ cvs -d :pserver:anonymous@pserver.git.sv.gnu.org:/gnulib.git co -d gnulib HEAD
Gnulib is hosted on savannah.gnu.org. The project page is
http://savannah.gnu.org/projects/gnulib.
Keeping Up-to-date
==================
The best way to work with Gnulib is to check it out of git.
Subscribing to the bug-gnulib@gnu.org mailing list will help you to
plan when to update your local copy of Gnulib (which you use to
maintain your software) from git. To synchronize, you can use "git pull",
or "cvs update -dP" if you are still using CVS.
Sometimes, using an updated version of Gnulib will require you to use
newer versions of GNU Automake or Autoconf. You may find it helpful
to join the autotools-announce mailing list to be advised of such
changes.
Contributing to Gnulib
======================
All software here is copyrighted by the Free Software Foundation - you need
to have filled out an assignment form for a project that uses the
module for that contribution to be accepted here.
If you have a piece of code that you would like to contribute, please
email bug-gnulib@gnu.org. You can review the archives, subscribe, etc.,
via http://lists.gnu.org/mailman/listinfo/bug-gnulib.
Generally we are looking for files that fulfill at least one of the
following requirements:
* If your .c and .h files define functions that are broken or
missing on some other system, we should be able to include it.
* If your functions remove arbitrary limits from existing
functions (either under the same name, or as a slightly different
name), we should be able to include it.
If your functions define completely new but rarely used functionality,
you should probably consider packaging it as a separate library.
License
-------
Gnulib contains code both under GPL and LGPL. Because several packages
that use Gnulib are GPL, the files state they are licensed under GPL.
However, to support LGPL projects as well, you may use some of the
files under LGPL. The "License:" information in the files under
modules/ clarifies the real license that applies to the module source.
Keep in mind that if you submit patches to files in Gnulib, you should
license them under a compatible license, which means that sometimes
the contribution will have to be LGPL, if the original file is
available under LGPL via a "License: LGPL" information in the
projects' modules/ file.
Indent with spaces, not TABs
----------------------------
We use space-only indentation in nearly all files. This includes all
*.h, *.c, *.y files, except for the regex module. Makefile and ChangeLog
files are excluded, since TAB characters are part of their format.
In order to tell your editor to produce space-only indentation, you
can use these instructions.
* For Emacs: Add these lines to your Emacs initialization file
($HOME/.emacs or similar):
;; In gnulib, indent with spaces everywhere (not TABs).
;; Exceptions: Makefile and ChangeLog modes.
(add-hook 'find-file-hook '(lambda ()
(if (and buffer-file-name
(string-match "/gnulib\\>" (buffer-file-name))
(not (string-equal mode-name "Change Log"))
(not (string-equal mode-name "Makefile")))
(setq indent-tabs-mode nil))))
* For vi (vim): Add these lines to your $HOME/.vimrc file:
" Don't use tabs for indentation. Spaces are nicer to work with.
set expandtab
For Makefile and ChangeLog files, compensate this by adding this to
your $HOME/.vim/after/indent/make.vim and
$HOME/.vim/after/indent/changelog.vim files:
" Use tabs for indentation, regardless of the global setting.
set noexpandtab
* For Eclipse: In the "Window|Preferences" dialog (or "Eclipse|Preferences"
dialog on Mac OS),
1. Under "General|Editors|Text Editors", select the "Insert spaces for tabs"
checkbox.
2. Under "C/C++|Code Style", select a code style profile that has the
"Indentation|Tab policy" combobox set to "Spaces only", such as the
"GNU [built-in]" policy.
If you use the GNU indent program, pass it the option '--no-tabs'.
How to add a new module
-----------------------
* Add the header files and source files to lib/.
* If the module needs configure-time checks, write an autoconf
macro for it in m4/<module>.m4. See m4/README for details.
* Write a module description modules/<module>, based on modules/TEMPLATE.
* If the module contributes a section to the end-user documentation,
put this documentation in doc/<module>.texi and add it to the "Files"
section of modules/<module>. Most modules don't do this; they have only
documentation for the programmer (= gnulib user). Such documentation
usually goes into the lib/ source files. It may also go into doc/;
but don't add it to the module description in this case.
* Add the module to the list in MODULES.html.sh.
You can test that a module builds correctly with:
$ ./gnulib-tool --create-testdir --dir=/tmp/testdir module1 ... moduleN
$ cd /tmp/testdir
$ ./configure && make
Other things:
* Check the license and copyright year of headers.
* Check that the source code follows the GNU coding standards;
see <http://www.gnu.org/prep/standards>.
* Add source files to config/srclist* if they are identical to upstream
and should be upgraded in gnulib whenever the upstream source changes.
* Include header files in source files to verify the function prototypes.
* Make sure a replacement function doesn't cause warnings or clashes on
systems that have the function.
* Autoconf functions can use gl_* prefix. The AC_* prefix is for
autoconf internal functions.
* Build files only if they are needed on a platform. Look at the
alloca and fnmatch modules for how to achieve this. If for some
reason you cannot do this, and you have a .c file that leads to an
empty .o file on some platforms (through some big #if around all the
code), then ensure that the compilation unit is not empty after
preprocessing. One way to do this is to #include <stddef.h> or
<stdio.h> before the big #if.
Portability guidelines
----------------------
Gnulib code is intended to be portable to a wide variety of platforms,
not just GNU platforms. See the documentation section "Target Platforms"
for details.
Many Gnulib modules exist so that applications need not worry about
undesirable variability in implementations. For example, an
application that uses the 'malloc' module need not worry about (malloc
(0)) returning NULL on some Standard C platforms; and 'time_r' users
need not worry about localtime_r returning int (not char *) on some
platforms that predate POSIX 1003.1-2001.
Currently we assume at least a freestanding C89 compiler, possibly
operating with a C library that predates C89. The oldest environments
currently ported to are probably HP-UX 10.20 and IRIX 5.3, though we
are not testing these platforms very often.
Because we assume a freestanding C89 compiler, Gnulib code can include
<float.h>, <limits.h>, <stdarg.h>, and <stddef.h> unconditionally. It
can also assume the existence of <ctime.h>, <errno.h>, <fcntl.h>,
<locale.h>, <signal.h>, <stdio.h>, <stdlib.h>, <string.h>, and <time.h>.
Similarly, many modules include <sys/types.h> even though it's not even
in C99; that's OK since <sys/types.h> has been around nearly forever.
Even if the include files exist, they may not conform to C89.
However, GCC has a "fixincludes" script that attempts to fix most
C89-conformance problems. So Gnulib currently assumes include files
largely conform to C89 or better. People still using ancient hosts
should use fixincludes or fix their include files manually.
Even if the include files conform to C89, the library itself may not.
For example, strtod and mktime have some bugs on some platforms.
You can work around some of these problems by requiring the relevant
modules, e.g., the Gnulib 'mktime' module supplies a working and
conforming 'mktime'.
The GNU coding standards allow one departure from strict C99: Gnulib
code can assume that standard internal types like size_t are no wider
than 'long'. POSIX 1003.1-2001 and the GNU coding standards both
require 'int' to be at least 32 bits wide, so Gnulib code assumes this
as well. Gnulib code makes the following additional assumptions:
* Signed integer arithmetic is two's complement.
Previously, gnulib code sometimes assumed that signed integer
arithmetic wraps around, but modern compiler optimizations
sometimes do not guarantee this, and gnulib code with this
assumption is now considered to be questionable. For more, please
see the file doc/intprops.texi.
Some gnulib modules contain explicit support for the other signed
integer representations allowed by C99 (ones' complement and signed
magnitude), but these modules are the exception rather than the rule.
All practical gnulib targets use two's complement.
* There are no "holes" in integer values: all the bits of an integer
contribute to its value in the usual way.
* Addresses and sizes behave as if objects reside in a flat address space.
In particular:
- If two nonoverlapping objects have sizes S and T represented as
size_t values, then S + T cannot overflow.
- A pointer P points within an object O if and only if
(char *) &O <= (char *) P && (char *) P < (char *) (&O + 1).
- If an existing object has size S, and if T is sufficiently small
(e.g., 8 KiB), then S + T cannot overflow. Overflow in this case
would mean that the rest of your program fits into T bytes, which
can't happen in realistic flat-address-space hosts.
* Objects with all bits zero are treated as 0 or NULL. For example,
memset (A, 0, sizeof A) initializes an array A of pointers to NULL.
* Adding zero to a null pointer does not change the pointer.
For example, 0 + (char *) NULL == (char *) NULL.
The above assumptions are not required by the C or POSIX standards but
hold on all practical porting targets that we're familiar with. If
you have a porting target where these assumptions are not true, we'd
appreciate hearing of any fixes. We need fixes that do not increase
runtime overhead on standard hosts and that are relatively easy to
maintain.
With the above caveats, Gnulib code should port without problem to new
hosts, e.g., hosts conforming to C99 or to recent POSIX standards.
Hence Gnulib code should avoid using constructs (e.g., undeclared
functions return 'int') that do not conform to C99.
High Quality
============
We develop and maintain a testsuite for Gnulib. The goal is to have a
100% firm interface so that maintainers can feel free to update to the
code in git at *any* time and know that their application will not
break. This means that before any change can be committed to the
repository, a test suite program must be produced that exposes the bug
for regression testing. All experimental work should be done on
branches to help promote this.
-----
Copyright 2001, 2003-2012 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
Please see doc/gnulib-readme.texi for basic information about Gnulib.
@c Gnulib README
@c Copyright 2001, 2003-2012 Free Software Foundation, Inc.
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3
@c or any later version published by the Free Software Foundation;
@c with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
@c Texts. A copy of the license is included in the ``GNU Free
@c Documentation License'' file as part of this distribution.
@menu
* Gnulib Basics::
* git and CVS::
* Keeping Up-to-date::
* Contributing to Gnulib::
* High Quality::
@end menu
@node Gnulib Basics
@section Gnulib Basics
While portability across operating systems is not one of GNU's primary
goals, it has helped introduce many people to the GNU system, and is
worthwhile when it can be achieved at a low cost. This collection helps
lower that cost.
Gnulib is intended to be the canonical source for most of the important
``portability'' and/or common files for GNU projects. These are files
intended to be shared at the source level; Gnulib is not a typical
library meant to be installed and linked against. Thus, unlike most
projects, Gnulib does not normally generate a source tarball
distribution; instead, developers grab modules directly from the
source repository.
The easiest, and recommended, way to do this is to use the
@command{gnulib-tool} script. Since there is no installation
procedure for Gnulib, @command{gnulib-tool} needs to be run directly
in the directory that contains the Gnulib source code. You can do
this either by specifying the absolute filename of
@command{gnulib-tool}, or by using a symbolic link from a place inside
your @env{PATH} to the @command{gnulib-tool} file of your preferred
Gnulib checkout. For example:
@example
$ ln -s $HOME/gnu/src/gnulib.git/gnulib-tool $HOME/bin/gnulib-tool
@end example
The home page for Gnulib is @url{http://www.gnu.org/software/gnulib}.
@node git and CVS
@section git and CVS
Gnulib is available for anonymous checkout. In any Bourne-shell the
following should work:
@example
$ git clone git://git.sv.gnu.org/gnulib.git
@end example
For a read-write checkout you need to have a login on
@samp{savannah.gnu.org} and be a member of the Gnulib project at
@url{http://savannah.gnu.org/projects/gnulib}. Then, instead of the
URL @url{git://git.sv.gnu.org/gnulib}, use the URL
@samp{ssh://@var{user}@@git.sv.gnu.org/srv/git/gnulib} where
@var{user} is your login name on savannah.gnu.org.
git resources:
@table @asis
@item Overview:
@url{http://en.wikipedia.org/wiki/Git_(software)}
@item Homepage:
@url{http://git.or.cz/}
@item Download:
@url{http://www.kernel.org/pub/software/scm/git/}
@item Tutorial:
@url{http://git.or.cz/course/}
@url{http://www.kernel.org/pub/software/scm/git/docs/tutorial.html}
@item FAQ:
@url{http://git.or.cz/gitwiki/GitFaq}
@end table
When you use @code{git annotate} or @code{git blame} with Gnulib, it's
recommended that you use the @option{-w} option, in order to ignore
massive whitespace changes that happened in 2009.
CVS checkouts are also supported:
@example
$ cvs -d :pserver:anonymous@@pserver.git.sv.gnu.org:/gnulib.git co -d gnulib HEAD
@end example
Gnulib is hosted on @samp{savannah.gnu.org}. The project page is
@url{http://savannah.gnu.org/projects/gnulib}.
@node Keeping Up-to-date
@section Keeping Up-to-date
The best way to work with Gnulib is to check it out of git.
Subscribing to the @email{bug-gnulib@@gnu.org} mailing list will help you to
plan when to update your local copy of Gnulib (which you use to
maintain your software) from git. To synchronize, you can use @code{git pull},
or @code{cvs update -dP} if you are still using CVS.
Sometimes, using an updated version of Gnulib will require you to use
newer versions of GNU Automake or Autoconf. You may find it helpful
to join the autotools-announce mailing list to be advised of such
changes.
@node Contributing to Gnulib
@section Contributing to Gnulib
All software here is copyrighted by the Free Software Foundation---you need
to have filled out an assignment form for a project that uses the
module for that contribution to be accepted here.
If you have a piece of code that you would like to contribute, please
email @email{bug-gnulib@@gnu.org}. You can review the archives,
subscribe, etc., via
@url{http://lists.gnu.org/mailman/listinfo/bug-gnulib}.
Generally we are looking for files that fulfill at least one of the
following requirements:
@itemize
@item
If your @file{.c} and @file{.h} files define functions that are broken or
missing on some other system, we should be able to include it.
@item
If your functions remove arbitrary limits from existing
functions (either under the same name, or as a slightly different
name), we should be able to include it.
@end itemize
If your functions define completely new but rarely used functionality,
you should probably consider packaging it as a separate library.
@menu
* Gnulib licensing::
* Indent with spaces not TABs::
* How to add a new module::
* Portability guidelines::
@end menu
@node Gnulib licensing
@subsection Gnulib licensing
Gnulib contains code both under GPL and LGPL@. Because several packages
that use Gnulib are GPL, the files state they are licensed under GPL@.
However, to support LGPL projects as well, you may use some of the
files under LGPL@. The ``License:'' information in the files under
modules/ clarifies the real license that applies to the module source.
Keep in mind that if you submit patches to files in Gnulib, you should
license them under a compatible license, which means that sometimes
the contribution will have to be LGPL, if the original file is
available under LGPL via a ``License: LGPL'' information in the
projects' modules/ file.
@node Indent with spaces not TABs
@subsection Indent with spaces not TABs
We use space-only indentation in nearly all files. This includes all
@file{*.h}, @file{*.c}, @file{*.y} files, except for the @code{regex}
module. Makefile and ChangeLog files are excluded, since TAB
characters are part of their format.
In order to tell your editor to produce space-only indentation, you
can use these instructions.
@itemize
@item
For Emacs: Add these lines to your Emacs initialization file
(@file{$HOME/.emacs} or similar):
@example
;; In Gnulib, indent with spaces everywhere (not TABs).
;; Exceptions: Makefile and ChangeLog modes.
(add-hook 'find-file-hook '(lambda ()
(if (and buffer-file-name
(string-match "/gnulib\\>" (buffer-file-name))
(not (string-equal mode-name "Change Log"))
(not (string-equal mode-name "Makefile")))
(setq indent-tabs-mode nil))))
@end example
@item
For vi (vim): Add these lines to your @file{$HOME/.vimrc} file:
@example
" Don't use tabs for indentation. Spaces are nicer to work with.
set expandtab
@end example
For Makefile and ChangeLog files, compensate this by adding this to
your @file{$HOME/.vim/after/indent/make.vim} and
@file{$HOME/.vim/after/indent/changelog.vim} files:
@example
" Use tabs for indentation, regardless of the global setting.
set noexpandtab
@end example
@item
For Eclipse: In the ``Window|Preferences'' dialog (or ``Eclipse|Preferences''
dialog on Mac OS),
@enumerate
@item
Under ``General|Editors|Text Editors'', select the ``Insert spaces for tabs''
checkbox.
@item
Under ``C/C++|Code Style'', select a code style profile that has the
``Indentation|Tab policy'' combobox set to ``Spaces only'', such as the
``GNU [built-in]'' policy.
@end enumerate
If you use the GNU indent program, pass it the option @option{--no-tabs}.
@end itemize
@node How to add a new module
@subsection How to add a new module
@itemize
@item
Add the header files and source files to @file{lib/}.
@item
If the module needs configure-time checks, write an Autoconf
macro for it in @file{m4/@var{module}.m4}. See @file{m4/README} for details.
@item
Write a module description @file{modules/@var{module}}, based on
@file{modules/TEMPLATE}.
@item
If the module contributes a section to the end-user documentation,
put this documentation in @file{doc/@var{module}.texi} and add it to the ``Files''
section of @file{modules/@var{module}}. Most modules don't do this; they have only
documentation for the programmer (= Gnulib user). Such documentation
usually goes into the @file{lib/} source files. It may also go into @file{doc/};
but don't add it to the module description in this case.
@item
Add the module to the list in @file{MODULES.html.sh}.
@end itemize
@noindent
You can test that a module builds correctly with:
@example
$ ./gnulib-tool --create-testdir --dir=/tmp/testdir module1 ... moduleN
$ cd /tmp/testdir
$ ./configure && make
@end example
@noindent
Other things:
@itemize
@item
Check the license and copyright year of headers.
@item
Check that the source code follows the GNU coding standards;
see @url{http://www.gnu.org/prep/standards}.
@item
Add source files to @file{config/srclist*} if they are identical to upstream
and should be upgraded in Gnulib whenever the upstream source changes.
@item
Include header files in source files to verify the function prototypes.
@item
Make sure a replacement function doesn't cause warnings or clashes on
systems that have the function.
@item
Autoconf functions can use @samp{gl_*} prefix. The @samp{AC_*} prefix is for
autoconf internal functions.
@item
Build files only if they are needed on a platform. Look at the
@code{alloca} and @code{fnmatch} modules for how to achieve this. If
for some reason you cannot do this, and you have a @file{.c} file that
leads to an empty @file{.o} file on some platforms (through some big
@code{#if} around all the code), then ensure that the compilation unit
is not empty after preprocessing. One way to do this is to
@code{#include <stddef.h>} or @code{<stdio.h>} before the big
@code{#if}.
@end itemize
@node Portability guidelines
@subsection Portability guidelines
Gnulib code is intended to be portable to a wide variety of platforms,
not just GNU platforms. See the documentation section ``Target Platforms''
for details.
Many Gnulib modules exist so that applications need not worry about
undesirable variability in implementations. For example, an
application that uses the @code{malloc} module need not worry about
@code{malloc@ (0)} returning @code{NULL} on some Standard C
platforms; and @code{time_r} users need not worry about
@code{localtime_r} returning @code{int} (not @code{char@ *}) on some
platforms that predate POSIX 1003.1-2001.
Currently we assume at least a freestanding C89 compiler, possibly
operating with a C library that predates C89. The oldest environments
currently ported to are probably HP-UX 10.20 and IRIX 5.3, though we
are not testing these platforms very often.
Because we assume a freestanding C89 compiler, Gnulib code can include
@code{<float.h>}, @code{<limits.h>}, @code{<stdarg.h>}, and
@code{<stddef.h>} unconditionally. It can also assume the existence
of @code{<ctime.h>}, @code{<errno.h>}, @code{<fcntl.h>},
@code{<locale.h>}, @code{<signal.h>}, @code{<stdio.h>},
@code{<stdlib.h>}, @code{<string.h>}, and @code{<time.h>}. Similarly,
many modules include @code{<sys/types.h>} even though it's not even in