Linux development process

Upstream and downstream

From the perspective of a linux distro, upstream usually refers to the original author(s) of the source code for a particular package. Downstream may refer to a distribution that has forked/branched from the perspective of the distro you are looking at.

So if Debian receives a bug relating to Apache, then a package maintainer or anyone reading the bugs may do some investigation. If they determine the bug to be in the original source code, and not caused by something unique to the distro they will work with the upstream authors to work on fixing the bug in program.

If the upstream developer of the troublesome package is uncooperative or went awol, then the investigating developer may add a patch to the package. This can be seen as a (hopefully temporary) fork of upstream development. Once bug and maintainer are found and bug is solved, Debian may work with downstream distros like Ubuntu to make sure the bug is fixed everywhere. Downstream maintainers can also submit issues related to things having to do with a packaging or any patches added.

If we are working on something like mint, which is based on ubuntu, which in turn is based on debian, the term upstream could mean any one of the maintainers of mint, ubuntu and debian, or it could refer to the original author(s) of a package. When maintainers and author(s) of packages are working well together usually all of them will be subscribed to similar lists, and bugtrackers and anyone with some responsibility for a given package will be notified in some form about bugs and new patches made at any level.

Kernel development

On occasion code is merged into the upstream kernel, the kernel tree managed by Linus Torvalds and available from kernel.org.

Merging source code upstream takes effort, dedication and time. The threshold for getting source code accepted into the Linux kernel is relatively high. If bad quality code got accepted, maintaining the linux kernel would become much more difficult.

Package development

Resources

Kernel

A Guide to the Kernel Development Process http://www.linuxfoundation.org/content/1-guide-kernel-development-process
The Linux Kernel Archives https://www.kernel.org/
The kernel guide http://www.linux.org/threads/linux-kernel-reading-guide.5384/
LinuxChanges http://kernelnewbies.org/LinuxChanges