Chapter 5. Source Tree Guidelines and Policies

Poul-Henning Kamp

Giorgos Keramidas

This chapter documents various guidelines and policies in force for the FreeBSD source tree.

5.1. Style Guidelines

Consistent coding style is extremely important, particularly with large projects like FreeBSD. Code should follow the FreeBSD coding styles described in style(9) and style.Makefile(5).

5.2. MAINTAINER on Makefiles

If a particular portion of the FreeBSD src/ distribution is being maintained by a person or group of persons, this is communicated through an entry in src/MAINTAINERS. Maintainers of ports within the Ports Collection express their maintainership to the world by adding a MAINTAINER line to the Makefile of the port in question:

MAINTAINER= email-addresses

For other parts of the repository, or for sections not listed as having a maintainer, or when you are unsure who the active maintainer is, try looking at the recent commit history of the relevant parts of the source tree. It is quite often the case that a maintainer is not explicitly named, but the people who are actively working in a part of the source tree for, say, the last couple of years are interested in reviewing changes. Even if this is not specifically mentioned in the documentation or the source itself, asking for a review as a form of courtesy is a very reasonable thing to do.

The role of the maintainer is as follows:

  • The maintainer owns and is responsible for that code. This means that he or she is responsible for fixing bugs and answering problem reports pertaining to that piece of the code, and in the case of contributed software, for tracking new versions, as appropriate.

  • Changes to directories which have a maintainer defined shall be sent to the maintainer for review before being committed. Only if the maintainer does not respond for an unacceptable period of time, to several emails, will it be acceptable to commit changes without review by the maintainer. However, it is suggested that you try to have the changes reviewed by someone else if at all possible.

  • It is of course not acceptable to add a person or group as maintainer unless they agree to assume this duty. On the other hand it does not have to be a committer and it can easily be a group of people.

5.3. Contributed Software

Some parts of the FreeBSD distribution consist of software that is actively being maintained outside the FreeBSD project. For historical reasons, we call this contributed software. Some examples are sendmail, gcc and patch.

Over the last couple of years, various methods have been used in dealing with this type of software and all have some number of advantages and drawbacks. No clear winner has emerged.

Since this is the case, after some debate one of these methods has been selected as the "official" method and will be required for future imports of software of this kind. Furthermore, it is strongly suggested that existing contributed software converge on this model over time, as it has significant advantages over the old method, including the ability to easily obtain diffs relative to the "official" versions of the source by everyone (even without direct repository access). This will make it significantly easier to return changes to the primary developers of the contributed software.

Ultimately, however, it comes down to the people actually doing the work. If using this model is particularly unsuited to the package being dealt with, exceptions to these rules may be granted only with the approval of the core team and with the general consensus of the other developers. The ability to maintain the package in the future will be a key issue in the decisions.

Because it makes it harder to import future versions minor, trivial and/or cosmetic changes are strongly discouraged on files that are still tracking the vendor branch.

5.3.1. Vendor Imports with SVN

This section describes the vendor import procedure with Subversion in details.

  1. Preparing the Tree

    If this is your first import after the switch to SVN, you will have to flatten and clean up the vendor tree, and bootstrap merge history in the main tree. If not, you can safely omit this step.

    During the conversion from CVS to SVN, vendor branches were imported with the same layout as the main tree. For example, the foo vendor sources ended up in vendor/foo/dist/contrib/foo, but it is pointless and rather inconvenient. What we really want is to have the vendor source directly in vendor/foo/dist, like this:

    % cd vendor/foo/dist/contrib/foo
    % svn move $(svn list) ../..
    % cd ../..
    % svn remove contrib
    % svn propdel -R svn:mergeinfo
    % svn commit

    Note that, the propdel bit is necessary because starting with 1.5, Subversion will automatically add svn:mergeinfo to any directory you copy or move. In this case, you will not need this information, since you are not going to merge anything from the tree you deleted.

    You may want to flatten the tags as well. The procedure is exactly the same. If you do this, put off the commit until the end.

    Check the dist tree and perform any cleanup that is deemed to be necessary. You may want to disable keyword expansion, as it makes no sense on unmodified vendor code. In some cases, it can be even be harmful.

    % svn propdel svn:keywords -R .
    % svn commit

    Bootstrapping of svn:mergeinfo on the target directory (in the main tree) to the revision that corresponds to the last change was made to the vendor tree prior to importing new sources is also needed:

    % cd head/contrib/foo
    % svn merge --record-only ^/vendor/foo/dist@12345678 .
    % svn commit

    With some shells, the ^ in the above command may need to be escaped with a backslash.

  2. Importing New Sources

    Prepare a full, clean tree of the vendor sources. With SVN, we can keep a full distribution in the vendor tree without bloating the main tree. Import everything but merge only what is needed.

    Note that you will need to add any files that were added since the last vendor import, and remove any that were removed. To facilitate this, you should prepare sorted lists of the contents of the vendor tree and of the sources you are about to import:

    % cd vendor/foo/dist
    % svn list -R | grep -v '/$' | sort > ../old
    % cd ../foo-9.9
    % find . -type f | cut -c 3- | sort > ../new

    With these two files, the following command will list removed files (files only in old):

    % comm -23 ../old ../new

    While the command below will list added files (files only in new):

    % comm -13 ../old ../new

    Let us put this together:

    % cd vendor/foo/foo-9.9
    % tar cf - . | tar xf - -C ../dist
    % cd ../dist
    % comm -23 ../old ../new | xargs svn remove
    % comm -13 ../old ../new | xargs svn add

    If there are new directories in the new distribution, the last command will fail. You will have to add the directories, and run it again. Conversely, if any directories were removed, you will have to remove them manually.

    Check properties on any new files:

    • All text files should have svn:eol-style set to native.

    • All binary files should have svn:mime-type set to application/octet-stream, unless there is a more appropriate media type.

    • Executable files should have svn:executable set to *.

    • There should be no other properties on any file in the tree.

      You are ready to commit, but you should first check the output of svn stat and svn diff to make sure everything is in order.

      Once you have committed the new vendor release, you should tag it for future reference. The best and quickest way is to do it directly in the repository:

      % svn copy ^/vendor/foo/dist svn_base/vendor/foo/9.9

      To get the new tag, you can update your working copy of vendor/foo.

      If you choose to do the copy in the checkout instead, do not forget to remove the generated svn:mergeinfo as described above.

  3. Merging to -HEAD

    After you have prepared your import, it is time to merge. Option --accept=postpone tells SVN not to handle merge conflicts yet, because they will be taken care of manually:

    % cd head/contrib/foo
    % svn update
    % svn merge --accept=postpone ^/vendor/foo/dist

    Resolve any conflicts, and make sure that any files that were added or removed in the vendor tree have been properly added or removed in the main tree. It is always a good idea to check differences against the vendor branch:

    % svn diff --no-diff-deleted --old=^/vendor/foo/dist --new=.

    --no-diff-deleted tells SVN not to check files that are in the vendor tree but not in the main tree.

    With SVN, there is no concept of on or off the vendor branch. If a file that previously had local modifications no longer does, just remove any left-over cruft, such as FreeBSD version tags, so it no longer shows up in diffs against the vendor tree.

    If any changes are required for the world to build with the new sources, make them now - and test until you are satisfied that everything build and runs correctly.

  4. Commit

    Now, you are ready to commit. Make sure you get everything in one go. Ideally, you would have done all steps in a clean tree, in which case you can just commit from the top of that tree. That is the best way to avoid surprises. If you do it properly, the tree will move atomically from a consistent state with the old code to a consistent state with the new code.

5.4. Encumbered Files

It might occasionally be necessary to include an encumbered file in the FreeBSD source tree. For example, if a device requires a small piece of binary code to be loaded to it before the device will operate, and we do not have the source to that code, then the binary file is said to be encumbered. The following policies apply to including encumbered files in the FreeBSD source tree.

  1. Any file which is interpreted or executed by the system CPU(s) and not in source format is encumbered.

  2. Any file with a license more restrictive than BSD or GNU is encumbered.

  3. A file which contains downloadable binary data for use by the hardware is not encumbered, unless (1) or (2) apply to it.

  4. Any encumbered file requires specific approval from the Core Team before it is added to the repository.

  5. Encumbered files go in src/contrib or src/sys/contrib.

  6. The entire module should be kept together. There is no point in splitting it, unless there is code-sharing with non-encumbered code.

  7. In the past binary files were typically uuencoded, and named arch/filename.o.uu. This is no longer necessary, and binary files may be added to the repository unchanged.

  8. Kernel files:

    1. Should always be referenced in conf/files.* (for build simplicity).

    2. Should always be in LINT, but the Core Team decides per case if it should be commented out or not. The Core Team can, of course, change their minds later on.

    3. The Release Engineer decides whether or not it goes into the release.

  9. User-land files:

    1. The Core team decides if the code should be part of make world.

    2. The Release Engineering decides if it goes into the release.

5.5. Shared Libraries

If you are adding shared library support to a port or other piece of software that does not have one, the version numbers should follow these rules. Generally, the resulting numbers will have nothing to do with the release version of the software.

For ports:

  • Prefer using the number already selected by upstream

  • If upstream provides symbol versioning, ensure that we use their script

For the base system:

  • Start library version from 1

  • It is strongly recommended to add symbol versioning to the new library

  • If there is an incompatible change, handle it with symbol versioning, maintaining backward ABI compatibility

  • If this is impossible, or the library does not use symbol versioning, bump the library version

  • Before even considering bumping library version for symbol-versioned library, consult with Release Engineering team, providing reasons why the change is so important that it should be allowed despite breaking the ABI

For instance, added functions and bugfixes not changing the interfaces are fine, while deleted functions, changed function call syntax, etc. should either provide backward-compat symbols, or will force the major version number to change.

It is the duty of the committer making the change to handle library versioning.

The ELF dynamic linker matches library names literally. There is a popular convention where library version is written in the form libexample.so.x.y, where x is the major version, and y is minor. Common practice is to set the library' soname (DT_SONAME ELF tag) to libexample.so.x, and set up symlinks libexample.so.x→libexample.so.x.y, libexample.so→libexample.so.x on library installation for the latest minor version y. Then, since the static linker searches for libexample.so when the -lexample command line option is specified, objects linked with libexample get a dependency on the right library. Almost all popular build systems use this scheme automatically.


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