For people who know me it should come with no surprise that I support free software in most forms it can take. I also believe that if someone gives you something at zero price, basic courtesy dictates that you follow wishes of that person. This is why when Software Freedom Conservancy started a GPL Compliance Project for Linux Developers I didn’t hesitate even for a minute to offer little Linux copyright I held to help the effort.

Most importantly though, it is why I fully support Conservancy in taking legal action against VMware which for years has been out of compliance with Linux’s license.

If you care about free software, the GPL or want more projects like OpenWrt, consider donating to help Christoph Hellwig and the Conservancy with their legal battle against this multi-billion-dollar corporation who for some reason decided to free-ride on other people’s work without respecting their wishes.

If you can’t or don’t want to donate, twitting something along the lines of ‘Play by the rules, @VMware. I defend the #GPL with Christoph & @Conservancy. #DTRTvmware Help at https://sfconservancy.org/supporter/’ or otherwise spreading the word will help as well. Oh, and in case you were, like I was, wondering — DTRT stands for ‘do the right thing’.

And if you want to know more:

• Press release
• LWN article

Don’t you hate when you need to do something you had done before, but cannot remember how exactly? I’ve been in that situation several times and sometimes looking up for a correct method turned out considerably harder than it should. To alleviate the need for future Googling, here’s a bag of notes I can reference easily:

• Getting past Chrome certificate error
• ‘Compressing’ git repository
• Changing commits author
• How to start a letter in English
• Summing numbers in a column in Emacs

Looking for Python stuff? Those are now in separate post:

• Converting date to timestamp
• Re-rising Python exception preserving back-trace
• Flattening a list in Python

Outside of functional programming context, map-reduce refers to a technique for processing data. Thanks to properties of map and reduce operations, computations which can be expressed using them can be highly parallelised, which allows for faster processing of high volumes of data.

If you’ve ever wondered how tools such as Apache Hadoop work, you’re at the right page. In this article I’ll explain what map and reduce are and later also introduce a shuffle phase.

Same as my previous article written in Polish, this text will describe some steps I take after installing Slackware Linux. I try to strike a balance between performance, security and usability, but not everything written here may work for everyone. You have been warned.

Cleaning Tiny Applications Collection, I’ve dropped both artificial intelligence scripts. Not wanting to let them disappear completely, I’m posting them here for posterity. The first one is an eight line of code version that might be what Sid wrote as his first ever program:

#!/usr/bin/perl -wWtT
while (<>) {
	if (/[aeiouyAEIOUY][^a-zA-Z]*$/) {
		print "Yes.\n";
	} elsif (!/^\s*$/) {
		print "No.\n";
	}
}

HTML has gone quite a long way since its inception. This means a lot of new features but also some small incompatibilities which may pose issues in certain situations. For instance, when posting a code snippet for others to include on their websites, it’s best if it works correctly on as many sites as possible which implies being compatible with as many versions of HTML as possible. But how to create a snippet that works both in HTML and XHTML? Here are a few tips:

CSS sprites aren’t anything new. They have been around for years, and are one of the methods to optimise website’s load time. The idea is to incorporate multiple images into one and in this way decrease number of round trips between the server and the browser.

In its traditional use, CSS sprites work as a replacement for images and cannot be used as a background. Alas that is exactly what I wanted to do with a quote and flag icons like the following:

Update: This website has evolved slightly since 2013. The flags are no longer used (replaced by content negotiation) and quote sprite icon has been replaced by an SVG. While I no longer use this technique, it is of course still valid.

After some playing around I’ve finally figured out how to get this working. Even though there are some caveats, sprites can be used as a top-left no-repeat background image as well.

Surprisingly I couldn’t find any HTTPS-aware examples how to drop the www. prefix from web hosts in Apache, so I had to come up with one myself. Firstly, the following lines need to find their way to the end of Apache configuration file (/etc/httpd/conf/httpd.conf or something):

RewriteEngine on
RewriteCond %{HTTPS} off
RewriteCond %{HTTP_HOST} ^www\.(.*)$
RewriteRule ^(.*)$ http://%1$1 [L,R=301]

Secondly, analogous lines need to be added inside of the <VirtualHost _default_:443> directive of mod_ssl configuration file (/etc/httpd/conf.d/ssl.conf or similar), like so:

<VirtualHost _default_:443>
	# … various directives …

	# Here’s what needs to be added:
	RewriteEngine on
	RewriteCond %{HTTP_HOST} ^www\.(.*)$
	RewriteRule ^(.*)$ https://%1$1 [L,R=301]
</VirtualHost>

Now, after a restart, Apache will drop the www. prefix for both secure and insecure connections.

Będę miał dzisiaj przyjemność prezentować Contiguous Memory Allocator na seminarium dyplomowym (CMA jest bowiem tematem mojej pracy). Dostępny jest również referat opisujący z większą zawartość slajdów. Aktualizacja: Z racji, że jestem już po obronie, dodaję również link do pracy inżynierskiej.

• Praca inżynierska, źródła.
• Prezentacja, źródła.
• Referat, źródła.

Prezentacja nie opisuje sposobu użycia CMA zatem po więcej szczegółów odsyłam do materiałów z LCE 2012. No i oczywiście jest również strona mina86.com/cma/, z której linkuję do przeróżnych materiałów dotyczących CMA.

LinuxCon / Embedded Linux Conference Europe 2012 is nearly over, and I had a pleasure of talking about the Contiguous Memory Allocator. Slides from the talk are available for download and their source code can be accessed at GitHub.

Unfortunately, in contrast to other LCE/ELCE conferences, talks were not recorded, so the video of the presentation is not available.

For more links regarding CMA, I have set up a resource page at mina86.com/cma/. Beside the link to the final CMA patchset and to the LCE/ELCE presentation, it links to various articles and patches relating to CMA directly or indirectly.