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=== General caracteristics ===
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=== Patching/unpatching targets includeable in debian/rules ===

||'''File''' ||'''Package'''||'''To patch''' ||'''To depatch'''||
||/usr/share/dpatch/dpatch.make || dpatch || patch || unpatch ||
||/usr/share/quilt/quilt.make || quilt || patch || unpatch ||
||/usr/share/cdbs/1/rules/patchsys-quilt.mk || quilt || apply-patches || reverse-patches ||
||/usr/share/cdbs/1/rules/simple-patchsys.mk|| cdbs || apply-patches || reverse-patches ||
||/usr/share/cdbs/1/rules/dpatch.mk || cdbs || apply-dpatches|| deapply-dpatches||

debian/patches

This page stems from the following discussion on debian-devel in January 2008: [http://lists.debian.org/msgid-search/alpine.DEB.1.00.0801250818360.5187@wr-linux02 alpine.DEB.1.00.0801250818360.5187@wr-linux02]. It also includes ideas from the discussion [http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=250202 #250202] about the Policy.

Existing systems

General caracteristics

Patch system

Location of the patches

How to inactivate a patch

Accepts diff -u output

Advantage

[http://packages.debian.org/dpatch dpatch]

debian/patches

Remove its name from debian/patches/00list

Header needs to be added

Can do scripting

[http://packages.debian.org/quilt quilt]

debian/patches

Remove its name from debian/patches/series

Yes

Suitable for generating patches on any size codebase. Advanced VCS-like features.

[http://packages.debian.org/cdbs cdbs] simple-patchsys

debian/patches

Remove its .diff or .patch suffix

Yes

Simple

[http://www.dpkg.org/dpkg/NewSourceFormat wig&pen]

debian/patches in .debian.tar.gz file

Rename to include a non-word non-hyphen character

Yes

Native to [http://packages.debian.org/dpkg dpkg]

[http://packages.debian.org/dbs dbs]

debian/patches

Remove it from the directory

Yes

Patches applied in ASCIIbetical order, no series file. Tarball-in-tarball (if you're in to that).

Patching/unpatching targets includeable in debian/rules

File

Package

To patch

To depatch

/usr/share/dpatch/dpatch.make

dpatch

patch

unpatch

/usr/share/quilt/quilt.make

quilt

patch

unpatch

/usr/share/cdbs/1/rules/patchsys-quilt.mk

quilt

apply-patches

reverse-patches

/usr/share/cdbs/1/rules/simple-patchsys.mk

cdbs

apply-patches

reverse-patches

/usr/share/cdbs/1/rules/dpatch.mk

cdbs

apply-dpatches

deapply-dpatches

Limitations

Users of a source package need the unpacked source not ready for compilation, but ready for inspection and modification. The two major use cases are application of (minor) local modifications (security fixes, compile time options) and manual or automated inspection of the source code (auditing, searching). This should be possible without installing additional packages besides dpkg-dev.

It has been discussed that the use of patch systems was making the work of porters, NMUers, security and QA teams difficult for two main reasons:

  1. The profusion of patch systems. People would have to learn them all and to be able to detect which one is used in the package they are working on.
  2. The difficulty to repack the sources. If direct modifications of source pacakages block the target unpatch, and if this target is called by clean, dpkg-buildpackage will fail.

  3. It is unclear whether Wig&Pen will be implemented and if yes, when. Some patch systems are not yet adapted to this format yet.

  4. Documents such as /usr/share/doc/debian/source-unpack.txt do not warn that modifications to the freshly unpacked sources can break the patching step.

Proposed improvements

  • Simply document how to patch the sources in a file called README.source, a template of which could be provided in the package of the patch system used.

  • Standardise the interface of the patch systems.
  • Use a single wrapper, possibly mandatory.
  • "Qualify" the systems which are widespread and durable, and discourage the use of others.
  • Make dpkg-source apply the patches automagically after unpacking the sources (using internal procedures).

  • Alternatively, make dpkg-source issue an informative message if it detects that a patch system is used.

  • Ship the sources patched (the clean target would call patch). Drawback: it bloats the diff.gz.

  • Implement a target called patched, that provides sources in such a state that calling debian/rules binary will not revert changes intrduced.

Rejected ideas

  • Make dpkg-source call the patching rule:

    • This is a security threat;
    • it would require the build-dependancies of a package to be installed.

A radical solution: not using any patch system anymore

Keeping a whole package, including upstream sources, in a version control system (VCS) has been proposed as an alternative way to manage the modification to upstream sources.

Comparison between the two paradigms

debian/patches

VCSes

Changes to upstream sources are divided in logical blocks that are the patches.

Changes to upstream sources are divided into logical blocks that are groups of commits.

dpkg-buildpackage can fail after modifications of the sources

dpkg-buildpackage can not be blocked by the impossibility to unpatch the sources.

The diff.gz file only contains files located in the debian directory

Informations conveyed by defining groups of commits is not reflected in the diff.gz file.

Well documented in beginners tutorials, strong tradition in packaging teams.

No tutorials for beginners, new and not widespread yet.

Repositories can be limited to contain only the debian directory.

Need to keep the upstream sources in a VCS as well.

Some systems, such as dpatch allow scripting.

Changes are systematically applied.

Of course, the use of VCS have other advantages, but this table focuses on the perspective of their substitution to patch management systems.

Unanswered questions

  • Groups of commits can be more messy that a well-documented patch: while a patch can be modified, a commit can only be reverted by another commit, adding even more complexity to the group of commit. How can the information contained in the logical breakdown of the modifications to upstream in a set of patches can be conveyed in the VCS paradigm?
  • The repository of packaging teams can contain up to hundreds of packages. How can they stay slim if they must contain upstream sources?
  • Is there somebody working on the Wig&Pen format ?

Future directions

If a consensus emerges, a [http://dep.debian.net/ Debian enhancement proposal] could be written.