4.4. Patching

In the preparation of the port, files that have been added or changed can be recorded with diff(1) for later feeding to patch(1). Doing this with a typical file involves saving a copy of the original file before making any changes using a .orig suffix.

% cp file file.orig

After all changes have been made, cd back to the port directory. Use make makepatch to generate updated patch files in the files directory.

4.4.1. General Rules for Patching

Patch files are stored in PATCHDIR, usually files/, from where they will be automatically applied. All patches must be relative to WRKSRC. Typically WRKSRC is a subdirectory of WRKDIR, the directory where the distfile is extracted. Use make -V WRKSRC to see the actual path. The patch names are to follow these rules:

  • Avoid having more than one patch modify the same file. For example, having both patch-foobar.c and patch-foobar.c2 making changes to ${WRKSRC}/foobar.c makes them fragile and difficult to debug.

  • When creating names for patch files, replace slashes (/) with two underscores (__). For example, to patch a file named src/freeglut_joystick.c, name the corresponding patch patch-src__freeglut_joystick.c. Do not name patches like patch-aa or patch-ab. Always use the path and file name in patch names. Using make makepatch automatically generates the correct names.

  • A patch may modify multiple files if the changes are related and the patch is named appropriately. For example, patch-add-missing-stdlib.h.

  • Only use characters [-+._a-zA-Z0-9] for naming patches. In particular, do not use :: as a path separator, use __ instead.

Minimize the amount of non-functional whitespace changes in patches. It is common in the Open Source world for projects to share large amounts of a code base, but obey different style and indenting rules. When taking a working piece of functionality from one project to fix similar areas in another, please be careful: the resulting patch may be full of non-functional changes. It not only increases the size of the ports repository but makes it hard to find out what exactly caused the problem and what was changed at all.

If a file must be deleted, do it in the post-extract target rather than as part of the patch.

4.4.2. Manual Patch Generation

Note:

Manual patch creation is usually not necessary. Automatic patch generation as described earlier in this section is the preferred method. However, manual patching may be required occasionally.

Patches are saved into files named patch-* where * indicates the pathname of the file that is patched, such as patch-Imakefile or patch-src-config.h.

After the file has been modified, diff(1) is used to record the differences between the original and the modified version. -u causes diff(1) to produce unified diffs, the preferred form.

% diff -u file.orig file > patch-pathname-file

When generating patches for new, added files, -N is used to tell diff(1) to treat the non-existent original file as if it existed but was empty:

% diff -u -N newfile.orig newfile > patch-pathname-newfile

Do not add $FreeBSD$ RCS strings in patches. When patches are added to the Subversion repository with svn add, the fbsd:nokeywords property is set to yes automatically so keywords in the patch are not modified when committed. The property can be added manually with svn propset fbsd:nokeywords yes files....

Using the recurse (-r) option to diff(1) to generate patches is fine, but please look at the resulting patches to make sure there is no unnecessary junk in there. In particular, diffs between two backup files, Makefiles when the port uses Imake or GNU configure, etc., are unnecessary and should be deleted. If it was necessary to edit configure.in and run autoconf to regenerate configure, do not take the diffs of configure (it often grows to a few thousand lines!). Instead, define USE_AUTOTOOLS=autoconf:261 and take the diffs of configure.in.

4.4.3. Simple Automatic Replacements

Simple replacements can be performed directly from the port Makefile using the in-place mode of sed(1). This is useful when changes use the value of a variable:

post-patch:
      @${REINPLACE_CMD} -e 's|for Linux|for FreeBSD|g' ${WRKSRC}/README

Quite often, software being ported uses the CR/LF convention in source files. This may cause problems with further patching, compiler warnings, or script execution (like /bin/sh^M not found.) To quickly convert all files from CR/LF to just LF, add this entry to the port Makefile:

USES=	dos2unix

A list of specific files to convert can be given:

USES=	dos2unix
DOS2UNIX_FILES=	util.c util.h

Use DOS2UNIX_REGEX to convert a group of files across subdirectories. Its argument is a find(1)-compatible regular expression. More on the format is in re_format(7). This option is useful for converting all files of a given extension. For example, convert all source code files, leaving binary files intact:

USES=	dos2unix
DOS2UNIX_REGEX=	.*\.([ch]|cpp)

A similar option is DOS2UNIX_GLOB, which runs find for each element listed in it.

USES=	dos2unix
DOS2UNIX_GLOB=	*.c *.cpp *.h

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