我查rsync安装包，看到有buster和buster-backports两个版本；buster-backports这个版本应该是来自于testing或者unstable～
https://packages.debian.org/buster-backports/rsync
我的问题是，那些从testing或者unstable进入到buster-backports的软件包，是怎么筛选出来的？或者，符合哪些条件，就可以从testing进入到buster-backports？
我查了一下backports wiki，wiki提到backports主要是为了解决stable软件包版本太旧的问题，并主要考虑依赖问题。
所以，对于新版本的软件包，只要没有新依赖需求，就一定会下沉到stable么？
这个问题没有简单的答案。像 Debian 中大多数的事情一样， Debian Backports 也遵循其政策。
Backports are about additional features that are only offered in a new version, not a replacement for getting fixes into stable - use stable-updates for that. Backports tracks testing and only package versions included in testing are allowed in it, subject to a few expedient exceptions.
Before uploading please think about how useful the package is for stable users and if it is sensible to support the package for the full supported lifetime of a release cycle (stable and oldstable).
Don’t backport minor version changes without user visible changes or bugfixes.
To guarantee an upgrade path from stable+backports to the next stable, the package needs to be in testing. Security updates may be uploaded before the testing migration completes. Other short-term exceptions can be granted for e.g. library transitions, critical bugs on request from the Backports Team.
Please only upload package with a notable userbase. Backports is not a maintainer’s PPA; a user request for the package may be an indicator. Use common sense and if in doubt, ask about the package on the mailing list.
因此，要将一个包上传至 Debian Backports，要考虑：
大概明白了~
