FreeBSDNews.com

[How-To] Create your first FreeBSD kernel module

By Leave a Comment

User Abdelhadi Khiati shows us how to create a FreeBSD kernel module. Follow the link below for the full set of instructions.

userconfigFreeBSD is one of the biggest OSs in history. It is Unix flavored and based on the Berkeley Software Distribution. Even though Linux is dominating most of the servers market nowadays, FreeBSD still got its fair share (Netflix).
We won’t dive into the reasons why you would want to use FreeBSD as your OS for production (Not the purpose of this post).
I have been lucky enough to participate in Google Summer of Code with the FreeBSD foundation. I was amazed by the community surrounding it which was noob friendly and very helpful (Thank you FreeBSD <3).
I wanted to make a starting tutorial for people to write a simple module for kernel before diving inside more complicated kernel shizzle.

The kernel module that we will be working on is a simple event handler for the kernel. It will be composed of 2 parts, the event handling function, and the module declaration.

The module event handler is a function that handles different events for the module. Like the module being loaded, unloaded or on system shutdown.

You can find the different kind of events that the module can handle here .

MOD_LOAD is set when the module is being loaded inside the kernel.

MOD_UNLOAD is set when the module is unloaded from the kernel.

MOD_SHUTDOWN is set on system shutdown.

MOD_QUIESCE is set when the module is about to be unloaded.

Full tutorial: http://meltmes.kiloreux.me/create-your-first-freebsd-kernel-module/

Fun with FreeBSD Listen Queue Overflow by Tykling

By Leave a Comment

In this article, FreeNode #freebsd users Tykling & backflow analyze a queue overflow error message from a log of their jailhost. These users came up with a method to track these kinds of problems down should they occur again. Special thanks to the FreeBSD IRC channel for the constant help they provide to the FreeBSD community.

I have no idea what could be causing this. This jailhost is busy so it could be a lot of things. Seems to happen about every hour, perhaps some scheduled job?

Most results when you search for the error mention TCP services that can’t keep up with the connection rate to the TCP port. But since I didn’t know which TCP port I had some detective work to do.

The error from messages looked like this:

Oct  1 01:17:10 bong kernel: sonewconn: pcb 0xfffff800647962d0: Listen queue overflow: 151 already in queue awaiting acceptance (1 occurrences)
Oct  1 02:14:10 bong kernel: sonewconn: pcb 0xfffff800647962d0: Listen queue overflow: 151 already in queue awaiting acceptance (1 occurrences)
Oct  1 03:14:11 bong kernel: sonewconn: pcb 0xfffff800647962d0: Listen queue overflow: 151 already in queue awaiting acceptance (1 occurrences)
Oct  1 04:13:11 bong kernel: sonewconn: pcb 0xfffff800647962d0: Listen queue overflow: 151 already in queue awaiting acceptance (1 occurrences)
Oct  1 05:11:11 bong kernel: sonewconn: pcb 0xfffff800647962d0: Listen queue overflow: 151 already in queue awaiting acceptance (1 occurrences)

Finding the socket from the pcb id

The errors all have the same pcb 0xfffff800647962d0 so I need to find the matching socket. I can use netstat(1) for this: …

Read the full article: https://blog.tyk.nu/blog/fun-with-freebsd-listen-queue-overflow/

Thank you to Matt Olander for submitting the article. If you’d like to submit one, feel free to respond in the comments.

Performance Improvements for FreeBSD Kernel Debugging by Will Andrews

By Leave a Comment

This article by user Will Andrews discusses the methods used to extract information from the FreeBSD kernel, and offers a solution that provides a boost in performance for those looking to do kernel debugging.

We previously explored FreeBSD userspace coredumps. Backtrace’s debugging platform supports FreeBSD kernel coredumps too, and their traces share many features. They are constructed somewhat differently, and in the process of adding support for them, we found a way to improve performance for automated programs accessing them.

Generating kernel core files

A kernel core is typically only generated in exceptional circumstances. Unlike userspace processes, kernel routines cannot fault without sacrificing the machine’s availability. This means things like page faults and illegal instructions inside the kernel stop the machine, instead of just one process. At that point, in most cases, it is only usable enough to inspect its state in a debugger, or to generate a core file.

Full article: http://backtrace.io/blog/blog/2016/08/25/improving-freebsd-kernel-debugging/

[Blog] FreeBSD EFI GELI Support

By Leave a Comment

User Eric McCorkle follows up on work in refactoring the FreeBSD EFI boot / loader code. In this blog, he discusses his findings in EFI refactoring, boot crypto framework, GELI support, and kernel key injection. See the link below for his full report.

I have completed my work to add support for the GELI disk encryption system to the FreeBSD EFI boot loader.  This work started off intending to be a “simple” patch, but it became a much larger undertaking that ended up refactoring a significant portion of the EFI boot loader.

Regardless, the changeset is now usable and ready for testing.  It can be accessed on my GitHub.  I will be merging this periodically with the FreeBSD master in order to keep it up to date.

I am not recommending this for inclusion in the 11 release; it’s too big a change to incorporate this late in the game.

Design/Implementation Notes

This work breaks down into roughly four different components: …

Original blog: https://ericmccorkleblog.wordpress.com/2016/05/28/freebsd-geli-support/