-@node Library vs. Reusable Code
+@node Benefits
+@section Benefits of using Gnulib
+
+Gnulib is useful to enhance various aspects of a package:
+
+@itemize @bullet
+@item
+Portability: With Gnulib, a package maintainer can program against the
+POSIX and GNU libc APIs and nevertheless expect good portability to
+platforms that don't implement POSIX.
+
+@item
+Maintainability: When a package uses modules from Gnulib instead of code
+written specifically for that package, the maintainer has less code to
+maintain.
+
+@item
+Security: Gnulib provides functions that are immune against vulnerabilities
+that plague the uses of the corresponding commonplace functions. For
+example, @code{asprintf}, @code{canonicalize_file_name} are not affected
+by buffer sizing problems that affect @code{sprintf}, @code{realpath}.
+@code{openat} does not have the race conditions that @code{open} has. Etc.
+
+@item
+Reliability: Gnulib provides functions that combine a call to a system
+function with a check of the result. Examples are @code{xalloc},
+@code{xprintf}, @code{xstrtod}, @code{xgetcwd}.
+
+@item
+Structure: Gnulib offers a way to structure code into modules, typically
+one include file, one source code file, and one autoconf macro for each
+functionality. Modularity helps maintainability.
+@end itemize
+
+@node Library vs Reusable Code
@section Library vs. Reusable Code
Classical libraries are installed as binary object code. Gnulib is
There is no clear borderline between both areas.
For example, Gnulib has a facility for generating the name of backup
-files. While this task is entirely at the application level---no
-standard specifies an API for it---the na@"{@dotless{i}}ve code has
+files. While this task is entirely at the application level --- no
+standard specifies an API for it --- the na@"{@dotless{i}}ve code has
some portability problems because on some platforms the length of file
name components is limited to 30 characters or so. Gnulib handles
that.
Similarly, Gnulib has a facility for executing a command in a
subprocess. It is at the same time a portability enhancement (it
-works on GNU/Unix and Windows, compared to the classical
-@code{fork()}/@code{exec()} which is not portable to Windows), as well
+works on GNU, Unix, and Windows, compared to the classical
+@code{fork}/@code{exec} idiom which is not portable to Windows), as well
as an application aid: it takes care of redirecting stdin and/or
stdout if desired, and emits an error message if the subprocess
failed.
@section Modules
Gnulib is divided into modules. Every module implements a single
-facility. Modules can depend on other modules.
+facility. Modules can depend on other modules.
A module consists of a number of files and a module description. The
files are copied by @code{gnulib-tool} into the package that will use it,
the @file{m4/} subdirectory. Build scripts reside in the
@file{build-aux/} subdirectory.
-The module description contains the list of files---@code{gnulib-tool}
+The module description contains the list of files --- @code{gnulib-tool}
copies these files. It contains the module's
-dependencies---@code{gnulib-tool} installs them as well. It also
+dependencies --- @code{gnulib-tool} installs them as well. It also
contains the autoconf macro invocation (usually a single line or
-nothing at all)---@code{gnulib-tool} ensures this is invoked from the
+nothing at all) --- @code{gnulib-tool} ensures this is invoked from the
package's @file{configure.ac} file. And also a @file{Makefile.am}
-snippet---@code{gnulib-tool} collects these into a @file{Makefile.am}
+snippet --- @code{gnulib-tool} collects these into a @file{Makefile.am}
for the tailored Gnulib part. The module description and include file
specification are for documentation purposes; they are combined into
@file{MODULES.html}.
@item
It ensures consistency of the used autoconf macros and @file{Makefile.am}
rules with the source code. For example, source code which uses the
-@code{getopt_long} function---this is a common way to implement parsing
-of command line options in a way that complies with the GNU standards---
+@code{getopt_long} function --- this is a common way to implement parsing
+of command line options in a way that complies with the GNU standards ---
needs the source code (@file{lib/getopt.c} and others), the autoconf macro
which detects whether the system's libc already has this function (in
@file{m4/getopt.m4}), and a few @file{Makefile.am} lines that create the
For header files, such as @code{stdbool.h} or @code{stdint.h}, we provide
the substitute only if the system doesn't provide a correct one. The
template of this replacement is distributed in a slightly different name,
-with an added underscore, so that on systems which do provide a correct
+with @samp{.in} inserted before the @samp{.h} extension, so that on
+systems which do provide a correct
header file the system's one is used.
@subsection Enhancements of ISO C or POSIX functions
These are sometimes POSIX functions with GNU extensions also found in
-glibc--examples: @samp{getopt}, @samp{fnmatch}---and often new
-APIs---for example, for all functions that allocate memory in one way
+glibc --- examples: @samp{getopt}, @samp{fnmatch} --- and often new
+APIs --- for example, for all functions that allocate memory in one way
or the other, we have variants which also include the error checking
against the out-of-memory condition.
@subsection Portable general use facilities
-Examples are a module for copying a file---the portability problems
+Examples are a module for copying a file --- the portability problems
relate to the copying of the file's modification time, access rights,
-and extended attributes---or a module for extracting the tail
-component of a file name---here the portability to Woe32 requires a
+and extended attributes --- or a module for extracting the tail
+component of a file name --- here the portability to Woe32 requires a
different API than the classical POSIX @code{basename} function.
@subsection Reusable application code
@subsection Interfaces to external libraries
Examples are the @samp{iconv} module, which interfaces to the
-@code{iconv()} facility, regardless whether it is contained in libc or in
+@code{iconv} facility, regardless whether it is contained in libc or in
an external @code{libiconv}. Or the @samp{readline} module, which
interfaces to the GNU readline library.
Most modules are under the GPL. Some, mostly modules which can
reasonably be used in libraries, are under LGPL. The source files
always say "GPL", but the real license specification is in the module
-description file.
+description file. If the module description file says "GPL", it means
+"GPLv3+" (GPLv3 or newer, at the licensee's choice); if it says "LGPL",
+it means "LGPLv3+" (LGPLv3 or newer, at the licensee's choice).
+
+More precisely, the license specification in the module description
+file applies to the files in @file{lib/} and @file{build-aux/}. Different
+licenses apply to files in special directories:
+
+@table @file
+@item modules/
+Module description files are under this copyright:
+
+@quotation
+Copyright @copyright{} 200X-200Y Free Software Foundation, Inc.@*
+Copying and distribution of this file, with or without modification,
+in any medium, are permitted without royalty provided the copyright
+notice and this notice are preserved.
+@end quotation
+
+@item m4/
+Autoconf macro files are under this copyright:
+
+@quotation
+Copyright @copyright{} 200X-200Y Free Software Foundation, Inc.@*
+This file is free software; the Free Software Foundation
+gives unlimited permission to copy and/or distribute it,
+with or without modifications, as long as this notice is preserved.
+@end quotation
+
+@item tests/
+If a license statement is not present in a test module, the test files are
+under GPL. Even if the corresponding source module is under LGPL, this is
+not a problem, since compiled tests are not installed by ``make install''.
+
+@item doc/
+Documentation files are under this copyright:
+
+@quotation
+Copyright @copyright{} 2004-200Y Free Software Foundation, Inc.@*
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.3 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
+copy of the license is included in the section entitled ``GNU Free
+Documentation License''.
+@end quotation
+@end table
If you want to use some Gnulib modules under LGPL, you can do so by
passing the option @samp{--lgpl} to @code{gnulib-tool}. This will
replace the GPL header with an LGPL header while copying the source
-files to your package.
+files to your package. Similarly, if you want some Gnulib modules
+under LGPLv2+ (Lesser GPL version 2.1 or newer), you can do so by
+passing the option @samp{--lgpl=2} to @code{gnulib-tool}.
Keep in mind that when you submit patches to files in Gnulib, you should
license them under a compatible license. This means that sometimes the
Gnulib modules are continually adapted, to match new practices, to be
consistent with newly added modules, or simply as a response to build
-failure reports. We don't make releases, but instead recommend to use the
-newest version of Gnulib from the CVS, except in periods of major changes.
+failure reports. Gnulib is available in two qualities:
+
+@itemize
+@item
+There is the newest version of Gnulib from the Git repository. The
+source tree can also be fetched from a read-only CVS that mirrors the Git
+repository.
+
+@item
+We also make stable releases every two months, at
+@url{http://erislabs.net/ianb/projects/gnulib/}.
+@end itemize
+
+If you are willing to report an occasional regression, we recommend to
+use the newest version always, except in periods of major changes. Most
+Gnulib users do this. If you prefer stable releases, please use the
+newest stable release.
@node Openness
@section Openness
@code{gnulib-tool}.
@end enumerate
-This is achieved by the @samp{--local-dir} option of @code{gnulib-tool}.
-
+This is achieved by the @samp{--local-dir} option of @code{gnulib-tool}
+(@pxref{Extending Gnulib}).
projects / gnulib.git / blobdiff