Month: June 2007

Graduated

Today I received a long anticipated phone call from my mentor who took away the doubt and let me know that I graduated for my VWO exams at the Stedelijk Gymnasium Nijmegen, which is a matriculation exam.

With mixed feeling I look back at seven long years. It certainly shouldn’t have took 7 years, nor 6, not even 3. But espacially in my last few years I came to appreciate the tons of very different people with whom I spend the days. A diversity I won’t find in that extend within the students of Maths and Physics which I intend to study next year at the Radboud University in Nijmegen.

For one thing I certainly wouldn’t have want to have missed these last few years. Some say they’re the best of your life. I do really look forward to university, though.

For those interested, I’ve planned an “Examenfeest” with some others in a nice club in Nijmegen. Send me an e-mail if you happen to be in the neighborhood and care to join.

Syslets and other untrusted kernelspace programming

In the wake of creating true async. IO in the linux kernel Ingo worked on so called syslets. A syslet is nothing more than one async system call to chain together a few arbitrary system calls. An example syslet would be:

1. Read from file descriptor 123
2. If 1 returned with error, break
3. Write which was read to file descriptor 321
4. If 3 succeeded jump to 1 otherwise break

This is represented by a few struct’s linked together of which the first is passed on to the kernel with the syslet system call. The systemcall returns practically directly and eventually the application can be notified (or can wait) on the syslet to complete. This could safe an enormous amount of system calls. This means way less context switches, which is very good for performance.

Syslets dawn, in a very primitive manner, kernelspace scripting. But hey, wasn’t kernelside scripting the thing that all linux dev’s dreaded? Wasn’t it Linus who joked that he would be in a mental institute whilst releasing Linux 3 with a VB message pump? Yes, they’re afraid of putting untrusted programs/scripts in kernelspace and they’ll barely acknowledge that syslets is the first step.

The problem with the current full-featured scripting languages is that they are, well, full-features gone wrong: they’re bloated and not really secure. In kernelspace you can’t allow any memory except for the scripts’ own to be accessed, not to mention the restrictions on resources and virtual memory won’t help you there. Most scripting languages weren’t developed with these restrictions in mind. Most languages have got evil functions in dark corners of the standard library that will allow you to do really evil stuff with memory.

As far as I know only .net (thus mono) have got a quite rigorous trust framework build in. .Net is bloated and proprietary and Mono is still (and probably will never be) feature complete though still being very bloated.

A very simple safe language is what we need, of which a compiler daemon is running as a system service, with which untrusted userspace programs can have scripts running in the kernel. I’m tempted to use one of the brainf*ck JIT’s, they’re small enough to thoroughly review :).

A kernelspace interpreter would do to, though, as a PoC.

Linux 2.6.21-bw-r1

There isn’t a tree that contains reiser4, suspend2 and the gentoo patches — so I created one. This revision adds the -stable patches, new gentoo patches and some powertop patches.

One big patch: bw-r1-for-2.6.21.diff.bz2
Patches broken out: bw-r1-for-2.6.21.tar.bz2

To apply the one big patch, use: bzcat bw-r1-for-2.6.21.diff.bz2 | patch -p1 inside a vanilla 2.6.21.

Upgrading wordpress with git

I didn’t like upgrading wodpress much. Everytime I did it, I needed to re-apply all my little tweaks to the new wordpress. It took too much time.

I tried to diff -uNr on the current version I was running and the newer version and then applying the resulting diff to the current version, but it seems wordpress has been backporting changes so I got conflicts, quite a lot of them.

Because I was quite tired of porting my changes, I’ve tried git, the Source Code Managment tool used by the linux kernel, to do it for me:

I did this all in the parent directory of the root of blog.w-nz.com. This folder contains:

  • htdocs current installation (2.1.2)
  • 2.1.2 the unmodified wordpress
  • 2.2.0 the new wordpress I want to upgrade to

First, I created an empty git repository:

mkdir git; cd git; git init-db; cd ..

Then I copied over the unmodified version of wordpress I was running, and commited them:

cp 2.1.2/* git -R
cd git
git add *
git commit -a -s
cd ..

Then I copied over my current installation:

cp htdocs/* git -R
git status # lets see what changed

There are lots of files like uploads I want git to ignore, so I edit .gitignore to make git ignore them. There weren’t any files I added though, otherwise I’d had to run git add to let git know.

And let commit my changes:

git commit -a -s

Now, lets go back to the original commit — the clean 2.1.2 wordpress — and start a branch from there:

git checkout HEAD^ # HEAD^ means parent commit of HEAD: the previous commit
git checkout -b tmp # create a new branch tmp from here

Now I’m in a branch without my own changes, which was forked from the master branch. Lets apply the new wordpress on this branch:

cd ..
cp 2.2.0/* git -R
cd git
git status # see what changed

git-status showed me that there are a few new files in wordpress 2.2.0, I git-add-ed all of these new files. And then committed it all:

git commit -a -s

Now I’ve got two branches:

  • master which contains wordpress 2.1.2 with my own changes on top as a commit
  • tmp which is forked from the wordpress 2.1.2 from the master branch without my own changes but with the 2.2.0 changes on top

What I want to do is to reapply the 2.2.0 changes on top of my current changes’ commit instead of on top of the 2.1.2 commit. To do this, git has a very powerfull util called git-rebase:

git rebase master

This will search down the tree until the point where the current branch (tmp) forked from the target branch (master). Then it will re-apply all commits in between on the latest commit of the target branch.

Just like if I’d use diff/patch I get a merge conflict. git rebase lets me know this and git status shows me which one are these. The one little difference with the diff/patch approach is, that there are way less merge conflicts (git is smarter) and that the merge conflict are way easier to identify and they’re inline in the original files. Not to mention that when I would have fucked up I’d always have a way back.

After I fixed the merge conflict, I git update-index each conflicted file (to tell git it’s resolved) and git rebase --continue-ed.

Now I’ve got my updated wordpress in the git folder. Then I backuped the current, copied over from git and visited wp-admin/upgrade.php and I’m done :).

By the way: “I didn’t say Subversion doesn’t work. Subversion users are just ugly and stupid.” — Linus on this Google tech talk.

Sidenote, I switched from Hashcash to Akismet. Hashcash didn’t work anymore and Akismet theoretically should be the best solution because it isn’t based on security by obscurity.