// -*- mode:doc; -*- // vim: set syntax=asciidoc: [[patch-policy]] Patching a package ------------------ While integrating a new package or updating an existing one, it may be necessary to patch the source of the software to get it cross-built within Buildroot. Buildroot offers an infrastructure to automatically handle this during the builds. It supports three ways of applying patch sets: downloaded patches, patches supplied within buildroot and patches located in a user-defined global patch directory. Providing patches ~~~~~~~~~~~~~~~~~ Downloaded ^^^^^^^^^^ If it is necessary to apply a patch that is available for download, then it to the +_PATCH+ variable. It is downloaded from the same site as the package itself. It can be a single patch, or a tarball containing a patch series. This method is typically used for packages from Debian. Within Buildroot ^^^^^^^^^^^^^^^^ Most patches are provided within Buildroot, in the package directory; these typically aim to fix cross-compilation, libc support, or other such issues. These patch files should be named +--.patch+. A +series+ file, as used by +quilt+, may also be added in the package directory. In that case, the +series+ file defines the patch application order. .Notes - The patch files coming with Buildroot should not contain any package version reference in their filename. - The field ++ in the patch file name refers to the 'apply order'. Global patch directory ^^^^^^^^^^^^^^^^^^^^^^ The +BR2_GLOBAL_PATCH_DIR+ configuration file option can be used to specify a directory containing global package patches. See xref:packages-custom[] for details. How patches are applied ~~~~~~~~~~~~~~~~~~~~~~~ . Run the +_PRE_PATCH_HOOKS+ commands if defined; . Cleanup the build directory, removing any existing +*.rej+ files; . If +_PATCH+ is defined, then patches from these tarballs are applied; . If there are some +*.patch+ files in the package directory or in the a package subdirectory named ++, then: + * If a +series+ file exists in the package directory, then patches are applied according to the +series+ file; + * Otherwise, patch files matching +-*.patch+ are applied in alphabetical order. So, to ensure they are applied in the right order, it is hightly recommended to named the patch files like this: +--.patch+, where ++ refers to the 'apply order'. . Run the +_POST_PATCH_HOOKS+ commands if defined. If something goes wrong in the steps _3_ or _4_, then the build fails. Format and licensing of the package patches ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Patches are released under the same license as the software that is modified. A message explaining what the patch does, and why it is needed, should be added in the header commentary of the patch. You should add a +Signed-off-by+ statement in the header of the each patch to help with keeping track of the changes and to certify that the patch is released under the same license as the software that is modified. If the software is under version control, it is recommended to use the upstream SCM software to generate the patch set. Otherwise, concatenate the header with the output of the +diff -purN package-version.orig/ package-version/+ command. At the end, the patch should look like: --------------- configure.ac: add C++ support test signed-off-by John Doe --- configure.ac.orig +++ configure.ac @@ -40,2 +40,12 @@ AC_PROG_MAKE_SET + +AC_CACHE_CHECK([whether the C++ compiler works], + [rw_cv_prog_cxx_works], + [AC_LANG_PUSH([C++]) + AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])], + [rw_cv_prog_cxx_works=yes], + [rw_cv_prog_cxx_works=no]) + AC_LANG_POP([C++])]) + +AM_CONDITIONAL([CXX_WORKS], [test "x$rw_cv_prog_cxx_works" = "xyes"]) --------------- Integrating patches found on the Web ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When integrating a patch of which you are not the author, you have to add a few things in the header of the patch itself. Depending on whether the patch has been obtained from the project repository itself, or from somewhere on the web, add one of the following tags: --------------- Backported from: --------------- or --------------- Fetch from: --------------- It is also sensible to add a few words about any changes to the patch that may have been necessary.