Extensions 扩展

Extensions are additional packages which client machines can install using package layering. While rpm-ostree itself is indifferent on the subject, most rpm-ostree-based distros encourage a containerized workflow for better separation of host and application layers. But sometimes, containerization is not ideal for some software, and yet it may not be desirable to bake them into the OSTree commit by default.
扩展是客户端机器可以使用包层叠安装的附加包。虽然 rpm-ostree 本身对此并不在意，但大多数基于 rpm-ostree 的发行版鼓励使用容器化工作流来更好地分离主机和应用层。但有时，对于某些软件来说，容器化并不是理想的选择，但又不希望默认将它们打包到 OSTree 提交中。

Package layering normally fetches such extensions from remote repos. However in some architectures there may be a better way to transfer them, or one may simply want tighter control over them and stronger binding between OSTree commit and extension versions (e.g. for reproducibility, guaranteed depsolve, QE, releng, etc..).
包层叠通常会从远程仓库获取这些扩展。然而，在某些架构中，可能有更好的方式来传输它们，或者一个人可能只是想更严格地控制它们，并加强 OSTree 提交与扩展版本之间的绑定（例如，为了可重现性、保证依赖解决、QE、releng 等）。

rpm-ostree compose extensions takes an extensions.yaml file describing OS extensions (packages) and a base OSTree commit. After performing a depsolve, it downloads the extension packages and places them in an output directory.
rpm-ostree compose extensions 接受描述操作系统扩展（软件包）和基本 OSTree 提交的文件。在执行依赖解决后，它会下载扩展软件包并将它们放置在输出目录中。

This can then be used as part of the same (or related) pipeline that runs rpm-ostree compose tree to ship extension packages.
然后可以将其作为运行 rpm-ostree compose tree 以发送扩展软件包的同一（或相关）流水线的一部分。

extensions.yaml

The format of the extensions.yaml file is as follow:
extensions.yaml 文件的格式如下：

# Any additional repos to enable on top of treefile repos
repos:
  - myrepo

# Any modules to enable/install
modules:
  enable:
    - foo:bar
  install:
    - baz:boo/default

# The top-level object is a dict. The only supported key
# right now is `extensions`, which is a dict of extension
# names to extension objects.
extensions:
  # This can be whatever name you'd like. The name itself
  # isn't used by rpm-ostree.
  sooper-dooper-tracers:
    # Optional; defaults to `os-extension`. An OS extension
    # is an extension intended to be `rpm-ostree install`ed.
    kind: os-extension
    # List of packages for this extension
    packages:
        - strace
        - ltrace
    # Optional additional repos (still added globally).
    # The reason use per-extension `repos` and `modules`
    # is that it more closely groups them (where relevant)
    # and further these are only added after architecture conditionals
    # apply, so one can use repositories that only exist
    # on a particular architecture.
    repos:
      - sooper-repo
    # Optional additional modules (this also affects global state)
    modules:
      enable:
        - sooper:latest
    # Optional list of architectures on which this extension
    # is valid. These are RPM basearches. If omitted,
    # defaults to all architectures.
    architectures:
        - x86_64
        - aarch64
  kernel-dev:
    # A development extension lists packages useful for
    # developing for the target OSTree, but won't be layered
    # on top. A common example is kernel modules. No
    # depsolving happens, packages listed are downloaded.
    kind: development
    packages:
      - kernel-devel
      - kernel-headers
    # Optional name of a base package used to constrain the
    # EVR of all the packages in this extension.
    match-base-evr: kernel