Entries posted in February 2009

It is funny the way things work out when you're looking for help.

Recently I was working on a Ruby + FUSE based filesystem and as part of the development I added simple diagnostic output via trivial code such as this:

@debug && puts "called foo(#{param});"

That was adequate for minimal interactive use, but not so good for real live use. In real live use I started outputing messages to a dedicated logfile, but in practise became overwhelmed by thousands of lines of output describing everything ever applied to the filesystem.

I figured the natural solution was to have a ring-buffer. (Everybody knows what a ringbuffer is, right?) It could keep the last 500 messages and newer debug information would just replace older entreis. That'd be just enough to be useful if I had a problem, but not so overwhelming it would get ignored.

In Perl I found a nice ringbuffer library, but for Ruby nothing. Locking a region of shared memory via shmget, shmset and keeping an array of a few hunded strings would be simple, but it seems odd I have to code this myself.

I started searching around and I accidentally stumbled upon the unrelated IPC::DirQueue perl module. Not useful for my ringbuffer logging problem, but beautifully useful.

There is no package for Debian but that was easily created:

dh-make-perl --build --cpan IPC::DirQueue

Already I have a million and one uses for it - not least to solve my problem of maintaining a centralised quarantine for all the spam mail rejected by N MX machines. (Which currently uses a combination of rsync and lockfiles.)

This is the reason why sites like Perl Advent Calendar are useful - they introduce a useful module every day or two, and introduce you to thinks that you can use in the future.

Of course keeping a sustainable site like that up and running is hard which is why sites like debaday struggle to attract contributors, for example.

Anyway random happyness.

ObFilm: Lord of the rings: Two Towers

Tags: fuse, perl, random, ruby | 3 comments

This weekend I have mostly been investigating Common Lisp.

If you're new to the environment then you may get started via a simple:

apt-get install clisp

Once you've done that the following resources will help you decide whether you're wasting your time or not:

• Practical Common Lisp
• The Common Lisp Cookbook

It has been a long time since I've had so much fun - even though the first thing I did was experiment with implementing a spam filter - although in my defense I was only classifying based upon the links contained in the mails. So for example:

• http://gmail.com/ - Good.
• http://www.facebook.com/ - Good. (ha!)
• http://tallbear.com - Spam
• http://pamperflow.com - Spam

(NSFW links)

ObFilm: Batman

Tags: clisp, common-lisp, lisp | 1 comment

I think I've made the decision that at some point in the next few months the xen-hosting.org setup I maintain will be going away, and will be replaced with kvm-hosting(.org).

The only issue I need to ponder is handling the migration with the minimum downtime.

The plan would probably involve upgrading the host machine to Lenny, then installing KVM and fiddling with filesystems until the guests boot. I suspect it wouldn't be a huge job, but there are a few issues that will need to be planned.

Most notably I expect that most of the current guests don't have grub installed, etc, so we'd be in the position to use an external kernel + initrd. That's not an insurmountable problem, but I know that externally supplied kernels have caused me problem in the past with KVM.

Perhaps the actual plan would be to wait until September at which point I could order a new machine and cancel the current one. That would mean another increase in spec and the migration process would be a lot simpler - instead of everybody being offline for a few hours I could migrate guests individually from the old host to the new.

Anyway decisions decisions ..

ObFilm: Buffy - But we'll pretend the TV series counts as a film, kthxbye?

Tags: kvm, xen, xen-hosting | 13 comments

Since I already shared it elsewhere here is my KVM-launcher, and the mercurial repository it lives in.

I'll add my kvm-shell program later - the tools I've written so far is mostly standalone, rather than a package.

This is almost a content-free post, but I can pretend it isn't because I'm testing a new theme on my blog. The theme is included in the new release of my chronicle blog compiler which was released yesterday.

ObFilm: Heathers

Tags: blogging, chronicle, kvm | No comments