Author: Anoop C S

Free Software enthusiast and Open Source developer

Mandatory locks support with GlusterFS v3.8

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antmascot

Latest version 3.8 from GlusterFS community comes out with the support for Mandatory locks. Please refer the blog post announcing the release to get an overview of all new features delivered with 3.8. This article will be a background cum architectural analysis on mandatory locks feature for GlusterFS and its further possibilities when working under various protocol environments.

Traditional/Advisory locks
Whenever it comes to a situation where file contents are being concurrently accessed by different applications there always raise the Read More »

Systemd defaults KillUserProcesses to ‘yes’ in logind.conf with v230

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Isn’t it strange what systemd has done with its latest release version 230 regarding user background process and login sessions? Or is it just me who feels so? Anyway in this post I am going to analyse this change[1] in default setting of logind.conf that upstream has released recently. Let me kick off with the following snippet taken from changelog of v230:

>>> systemd-logind will now by default terminate user processes that are part of the user session scope unit (session-XX.scope) when the user logs out. This behavior is controlled by the KillUserProcesses= setting in logind.conf, and the previous default of “no” is now changed to “yes”. This means that user sessions will be properly cleaned up after, but additional steps are necessary to allow intentionally long-running processes to survive logout. <<<

Click here for complete changes with v230 release.

So what does that mean? I can explain the above change citing the example of GNU Screen. For an average GNU/Linux user it is not an Read More »

POSIX deadlock detection: A walk through linux kernel source

Anoop C S2 Comments

A note to readers: The following content is completely oriented for developers, especially in C. In case you find it difficult to understand certain terms, please help yourselves to google around and understand the concepts. I have tried including links wherever necessary in order to effectively interpret the article(see provided links towards the end). Last but not least, as per POSIX documentation[1], deadlock detection is guaranteed for locks between different processes and not between different threads inside a process or between threads belonging to different processes.

As you can see from the heading of this article, I am aiming at explaining the source code for detecting POSIX deadlocks. Before that let me quickly brief the concept of deadlock in operating systems. A deadlock is a situation where two processes sharing the same resource are preventing each other from accessing the resource which will result in an undefined wait for those resources. Following are the four necessary conditions(Coffman conditions)[2] which leads to a deadlock scenario:

* Mutual exclusion
* Hold and Wait
* No pre-emption
* Circular wait

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