Portability has always been very important to Samba. Nowadays Samba is mostly used on top of Linux, but Tridge developed the early versions of his SMB implementation on a Sun workstation.
A few years later, when the project was being picked up, it was ported to Linux and eventually to a large number of other free and non-free Unix-like operating systems.
Initially regression testing on different platforms was done manually and ad-hoc.
Once Samba had support for a larger number of platforms, including numerous variations and optional dependencies, making sure that it would still build and run on all of these became a non-trivial process.
To make it easier to find regressions in the Samba codebase that were platform-specific, tridge put together a system to automatically build Samba regularly on as many platforms as possible. So, in Spring 2001, the build farm was born - this was a couple of years before other tools like buildbot came around.
The Build Farm
The build farm is a collection of machines around the world that are connected to the internet, with as wide a variety of platforms as possible. In 2001, it wasn't feasible to just have a single beefy machine or a cloud account on which we could run virtual machines with AIX, HPUX, Tru64, Solaris and Linux so we needed access to physical hardware.
The build farm runs as a single non-privileged user, which has a cron job set up that runs the build farm worker script regularly. Originally the frequency was every couple of hours, but soon we asked machine owners to run it as often as possible. The worker script is as short as it is simple. It retrieves a shell script from the main build farm repository with instructions to run and after it has done so, it uploads a log file of the terminal output to samba.org using rsync and a secret per-machine password.
Some build farm machines are dedicated, but there have also been a large number of the years that would just run as a separate user account on a machine that was tasked with something else. Most build farm machines are hosted by Samba developers (or their employers) but we've also had a number of community volunteers over the years that were happy to add an extra user with an extra cron job on their machine and for a while companies like SourceForge and HP provided dedicated porter boxes that ran the build farm.
Of course, there are some security usses with this way of running things. Arbitrary shell code is downloaded from a host claiming to be samba.org and run. If the machine is shared with other (sensitive) processes, some of the information about those processes might leak into logs.
Our web page has a section about adding machines for new volunteers, with a long list of warnings.
Since then, various other people have been involved in the build farm. Andrew Bartlett started contributing to the build farm in July 2001, working on adding tests. He gradually took over as the maintainer in 2002, and various others (Vance, Martin, Mathieu) have contributed patches and helped out with general admin.
In 2005, tridge added a script to automatically send out an e-mail to the committer of the last revision before a failed build. This meant it was no longer necessary to bisect through build farm logs on the web to find out who had broken a specific platform when; you'd just be notified as soon as it happened.
The web site
Once the logs are generated and uploaded to samba.org using rsync, the web site at http://build.samba.org/ is responsible for making them accessible to the world. Initially there was a single perl file that would take care of listing and displaying log files, but over the years the functionality has been extended to do much more than that.
Initial extensions to the build farm added support for viewing per-compiler and per-host builds, to allow spotting trends. Another addition was searching logs for common indicators of running out of disk space.
Over time, we also added more samba.org-projects to the build farm. At the moment there are about a dozen projects.
In a sprint in 2009, Andrew Bartlett and I changed the build farm to store machine and build metadata in a SQLite database rather than parsing all recent build log files every time their results were needed.
In a follow-up sprint a year later, we converted most of the code to Python. We also added a number of extensions; most notably, linking the build result information with version control information so we could automatically email the exact people that had caused the build breakage, and automatically notifying build farm owners when their machines were not functioning.
Sometime in 2011 all committers started using the autobuild script to push changes to the master Samba branch. This script enforces a full build and testsuite run for each commit that is pushed. If the build or any part of the testsuite fails, the push is aborted. This alone massively reduced the number of problematic changes that was pushed, making it less necessary for us to be made aware of issues by the build farm.
The rewrite also introduced some time bombs into the code. The way we called out to our ORM caused the code to fetch all build summary data from the database every time the summary page was generated. Initially this was not a problem, but as the table grew to 100,000 rows, the build farm became so slow that it was frustrating to use.
Over the years, various special build farm machines have also been used to run extra code analysis tools, like static code analysis, lcov, valgrind or various code quality scanners.
Summer of Code
Of the last couple of years the build farm has been running happily, and hasn't changed much.
This summer one of our summer of code students, Krishna Teja Perannagari, worked on improving the look of the build farm - updating it to the current Samba house style - as well as various performance improvements in the Python code.
The build farm still works reasonably well, though it is clear that various other tools that have had more developer attention have caught up with it. If we would have to reinvent the build farm today, we would probably end up using an off-the-shelve tool like Jenkins that wasn't around 14 years ago. We would also be able to get away with using virtual machines for most of our workers.
Non-Linux platforms have become less relevant in the last couple of years, though we still care about them.
The build farm in its current form works well enough for us, and I think porting to Jenkins - with the same level of platform coverage - would take quite a lot of work and have only limited benefits.
(Thanks to Andrew Bartlett for proofreading the draft of this post.)