Gear/Introduction

From ALT Linux Wiki

This is introduction to gear for the people who already have the RPM packaging experience and know how to use git.

Purpose of gear

gear provides a mean to build RPM packages from git repository, by providing

  • format of rules file, describing the steps to generate source package from repository
  • utilities for building packages and working with source code (importing upstream sources and managing patches)

RPM-specific stuff

RPM source packages are built from the following files:

  • .spec file, which is roughly debian/* without debian/patches/*
  • several source files/tarballs
  • and several patch-files.

gear provides the means to build/generate latter two types of files from the git, so repository is not required to contain them in the form digestible by rpmbuild.

Working with upstream source code

Upstream source code is generally stored in the separate branch.

There are two main sources of source code: upstream tarballs or upstream VCS, plus importing SRPMs for keeping older packaging history.

SRPMs

$ gear-srpmimport some-0.1.src.rpm
$ gear-srpmimport some-0.2.src.rpm
...

will import the given SRPMs to the branch ("srpms" by default) in the repository (like git-import-dsc).

Importing SRPM creates git layout similar to the "Like SRPM" scenario described below.

Tarballs

$ gear-update foo-0.2.tar.gz foo
$ gear-update foo-2.0.tar.gz foo
...

will update the subdirectory foo in git repository with contents of tarball. This operation is similar to the git-import-orig from dpkg-buildpackage. As SRPMs may contain several sources, the source code usually stored in the subdirectory.

Upstream VCS

This should be obvious: just fetch/pull if upstream uses git, or use converter if it does not.

Packaging and patching

There are three major scenarios for keeping changes in the repository:

  • like SRPM
  • patches in one branch
  • patches in topic branches

Scenario 1. "Like SRPM"

This is least useful, but simple scenario. git is used just for keeping history, and the usual maintainer's workflow is not changed.

Branches in repository: 

master
upstream

Tree layout: 

foo/                      (in upstream, master)
.gear/rules               (in master)
foo.spec                  (in master)
foo-something-fixed.patch (in master)
foo-another-fixed.patch   (in master)

git repository is generated by the importing SRPMs or by creating from scratch.

Importing tarball to the upstream branch

By using master branch to make it a bit easier 

$ mkdir foo
$ cd foo
$ git init foo
$ gear-update ../foo-1.0.tar.gz foo
$ git checkout -b upstream

Adding spec and patches

$ vi foo.spec
$ vi foo-something-fixed.patch
$ vi foo-another-fixed.patch

Adding gear/rules

The .gear/rules will have the following contents: 

copy: foo-something-fixed.patch
copy: foo-another-fixed.patch
tar.gz: foo

This will add both patches and tar.gz'ed directory foo/ to the buildroot where the package is built.

Specfile is picked up automatically if there is only .spec in the root directory fo git.

Commiting the stuff

gear is picky about it - it only handles the stuff which is in repo. 

$ git add .   # Commit entire workdir
$ gear-commit # this is wrapper around git-commit which uses the last
              # changelog entry as a commit message.

Scenario 2. "Small fixes"

This is scenario for the packages which need the small non-overlapping fixes here and there. This is also easiest scenario to use.

Branches in repository: 

master
upstream

Tree layout: 

foo/        (in upstream, patched in master)
.gear/rules (in master)
foo.spec    (in master)

Working on package

$ git checkout master
$ vim ...     # hack-hack
$ git add ... # add new files if needed (optional)
$ git commit

All the changes are applied just on top of the upstream source code.

.gear/rules

The .gear/rules file will be of the following form: 

tar: v@version@:foo
diff: diff: v@version@:foo foo

This will generate foo.tar, containing upstream source code, taken from the tag v${version}, where version is parsed from the foo.spec, and the diff with the difference between the directory foo in v${version} tag and the current directory foo.

gear does not use real git tags, but instead it uses the tags stored in .gear/tags.

This has the reasons: as tags may move over time, to achieve reproducibility of builds, tag position need to be stored in the git tree. There is utility for maintaining this set of tags: 

$ gear-update-tag --all

Don't forget to commit the changes after updating: 

$ git-commit .gear/tags -m 'tags updated'

Rebasing to new upstream version

$ git merge upstream
... Fix conflicts, update changelog, remove unnecesary patches etc ...
$ gear-commit

That's all! As patches are stored in git branch, it's easy to update to new upstream version: merge will detect most incosistences. As an additional bonus, if upstream uses git as well, patches forwarded upstream and accepted there will not generate conflicts on merge.

New package revision

$ vim ... # hack-hack, update changelog
$ gear-commit

Also simple.

Scenario 3. "Full-blown development"

This is scenario for the packages which need the lot of work downstream (e.g. kernel).

Branches: 

upstream
topic-A
topic-B
...
master

Tree layout: 

foo/        (in upstream, patched in topic-*, master)
.gear/rules (in master)
foo.spec    (in master)

Working on package

All the work is done in topic branches, each is dedicated for some topic: 

$ git checkout topic-A
$ vim ... # hack-hack-hack
$ git commit
$ git checkout topic-B
...

As patches may overlap, some conflict resolution need to be involved. The naive approach would be using the following branching scheme: 

* upstream
|
\--> topic-A
\--> topic-B
\--> master

And then generating patch-per-topic by using .gear/rules. This will not work, as the generated patches will conflict.

Instead, the following scheme is used: 

* upstream
\-> topic-A
    \-> topic-B
        \-> master

And gear-merge(1) utility merges the branches as described in .gear/merge file: 

merge: upstream topic-A
merge: topic-A topic-B
merge: topic-B master

After using this utility (and resolving all conflicts occupied), master branch gets a cumulative change.

.gear/rules

The .gear/rules file will be exactly the same as for previous scenario, so the gear-update-tag(1) is also required: 

tar: v@version@:foo
diff: diff: v@version@:foo foo

Rebasing to new upstream version

$ ... # obtain the new upstream code in upstream branch
$ gear-merge
... Fix conflicts, update changelog, remove unnecessary patches etc...
$ gear-commit

Due to gear-merge, it's only necessary to fix the conflicts once.

New package revision

$ vim ... # hack-hack, commit
$ gear-merge

Builds

$ gear-hsh

Here the .gear/rules is consulted and the following is performed:

  • pkg.tar package is constructed, according to the .gear/rules file
  • hasher is run with the given source package.

There are also another build-commands: gear-rpm (uses rpmbuild instead of hasher) and gear-remote-hsh/gear-remote-rpm, which use remote host for actual building (communicating over SSH).