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atoi(getenv(“MYVAR”))

Jacob — Wed, 28 May 2008 22:34:05 +0000

These are mostly personal notes. I’m not sure if they will make sense to others.

I had a problem with a line of code like this:
int x = atoi(getenv("MYVAR"));

If this line was in daemon-ized code started at init level 2, it would segfault. (I’m not sure if these conditions are necessary, but those were my conditions).

getenv("UNKNOWN_VAR") == NULL
atoi(NULL) should == 0

But for some reason, things were segfaulting. I corrected the problem with:
if (getenv("MYVAR") == NULL) int x = 0; else int x = atoi(getenv("MYVAR"));

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Death by writing files from the kernel

Jacob — Fri, 21 Mar 2008 16:00:52 +0000

I’ve written my first semi-major Linux device driver. I won’t say exactly what it does other than write data out to hardware.

Generally, it is well NOT accepted to write to files from the kernel. If you ask how, people will tell you “don’t.” I completely agree with all of the reasons provided, but I decided to do it anyway.

The hardware I’m writing data to isn’t readily available. I wanted to be able to test my code well without having to have the hardware available. So I wrote in some non-release, non-production code that writes data to a file instead of to hardware, but only for testing purposes. When in this simulation mode, the user can interact with the driver and data gets written to the file instead of to hardware, and then the file can be checked for accuracy.

User writes to driver -> kernel driver handles write -> driver writes to file

Easy enough? I thought so until I tried writing to the driver as a regular system user. I chmod’ed the driver so that the user had full privileges to read and write to the file. When root would write to the driver, everything worked, when the regular user would write to the driver, the kernel would crash.

The problem was that the user didn’t have write permissions to the test file that the driver was writing to. I thought the kernel level driver could write to any file it wanted, but apparently, the user’s permissions to the file permeated through the kernel driver. Changing the files permissions fixed things so they didn’t crash any more.

The caps lock and scroll lock lights blink on the keyboard when the kernel crashes. Not quite fireworks, but still kind of cool. Development in a virtual machine is key, so that you really don’t crash your computer, just the virtual machine.

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AverTV Media on Ubuntu

Jacob — Sat, 25 Aug 2007 20:47:14 +0000

I have an old TV tuner card that I picked up in 2002. I can’t remember exactly what type of card it is, but after searching around the internet, I’m somewhat convinced that it is the AverTV Media (with FM tuner). The card identifies itself as an AverTV Phone something or another, but I know it isn’t any of their “phone” variety of cards.

The card has an analog TV tuner, and FM tuner, composite in, s-video in, audio in and audio out (it mixes the audio in with the tuner’s audio and sends it to audio out).

I’m currently using Kubuntu 7.04.

When I first tried using the card, I saw somewhat of screwed up black and white video. I fixed it by creating a file /etc/modprobe.d/bttv which contains
options bttv card=6 gbuffers=8 audiomux=0x0e,0x04,0x08,0x04,0 gpiomask=0x0f tuner=2 radio=1
This allowed me to get video in to xawtv. When I tried running scantv, I got an error message back about “vbi: open failed [/dev/vbi]” but then I ran it again with scantv -C /dev/vbi0 and it worked.

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Keeping Linux under Ctrl-Ctrl

Jacob — Fri, 29 Jun 2007 02:23:55 +0000

Recently, Google released their Google Desktop product for Linux. I found out about it just this evening. Earlier today, I was searching through my home directory looking for some old files from a long time ago, and I though, “Wouldn’t it be great if Google Desktop Search was available for Linux?” About two hours later, my wish came true.

Installation was a piece of cake–I just installed the Ubuntu package, and I was up and going. I did run into one problem. When I first started it up, it tried hoping the home page in my Quanta code editor instead of Firefox. This is typically because when I open up web page files that are resident on my computer, I like to open them up in an editor so I can work on them. So having Google Desktop try to open itself up in an editor…. not so great, but easily fixed.

When Google came out with their Desktop product for Mac, I said that it would be HUGE if they could also release it for Linux. The power of having a product out for Windows, Mac and Linux is great for enterprise. Business IT departments can choose one single product, and roll it out to all their heterogeneous computing environments.

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Upgrading operating systems

Jacob — Fri, 20 Apr 2007 08:22:24 +0000

How would you respond if I told you that all it would take is a few clicks to upgrade your Windows XP to Wndows Vista? That it would be able to download and upgrade the entire system in a matter of hours (depending on the speed of your Internet connection). What if I said it would also upgrade your word processor, web browser, and most of the other commonly used applications? What if I said it wouldn’t even cost you a thing?

While this will most likely never be true for Windows, it is currently the case with Ubuntu Linux. With about half a dozen clicks, I was able to download and install the latest version of the operating system and most of my applications, just like that. All my data, documents, and preferences are preserved, because the updater is good at upgrading the system while leaving user files alone.

Another difference between Windows and Ubuntu Linux is that I didn’t have to wait 5 years for the latest release. In fact, I updated just six months ago. But there has been a lot of improvements and changes in the last six months, and I appreciate being able to take advantage of all the updates immediately. Since upgrading is so easy, it isn’t a big deal to have to upgrade.

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Drag and drop into Konsole

Jacob — Sat, 03 Feb 2007 02:04:13 +0000

I found a very cool thing today. I use KDE on Linux. One of the things I like best about KDE is that it supports psudo- filesystems such as fish, which allows you to access a remote filesystem over ssh. I wanted to copy a file that was on a remote system into a local directory. Without thinking, I did the mouse drag-and-drop action to move the file. Except that I dropped the file into Konsole, the KDE terminal program. A popup menu appeared with several options, one of which was ‘cp’ which I selected. The result was that the file was copied from the remote server to the current working directory in my KDE terminal. My terminal showed that it had run a command in order to copy the file, which was:

kfmclient copy ‘fish://username@remoteserver.com/tmp/filename’ .

This is extremely cool, and I’m definately going to have to use it a little bit more often.

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Linux development process

Jacob — Mon, 09 Oct 2006 22:37:07 +0000

Greg Kroah-Hartman came to my Open Source Software Engineering class today. Here are a couple of interesting thoughts that I’ve been able to gather from his presentation:

New patches are tested with Andrew’s mm kernel, and if they work out, then they are sent to Linus’ kernel.
Time between kernel versions should be about two months.
1475 unique contributors in one year alone
Grew kernel 6% in one year
2.6.18.y kernels are bugfixes only
Powerful to have a set list of rules so it is easy to say no to people
Day job: in charge of all SuSE kernel developers. All work remotely around the world.
Distros like to maintain an enterprise kernel for up to 7 years, which is crazy
E*Trade uses Gentoo because they can control it.
Modular kernel which little interconnectedness which makes it easy to have module maintainers who don’t
Tools: git, quilt, sparse
Linus’ main job: say no
Linux isn’t developed, it evolves. This means that there really isn’t a firm development plan.
Can’t go by time anymore with git
Signed-off-by is a blame path which create a reputation based system for submitting patches
The IDE module guy three times has gone crazy
Contributors have to defend their code
No development tree makes the engineering process more careful. Things have to evolve gradually with small changesets.
All the drivers are in the tree. This means that if you change an API function, then you can go and change all the drivers that use that API just like that.
People who work on open source projects are much more likely to get jobs, because you have currently shipping code.
Learn about licenses, they are very important.
Xen is a good example of running an open source project the wrong way. There are political and social reasons why.

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Webcam Links for Linux

Jacob — Thu, 02 Feb 2006 05:55:19 +0000

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Guide to setting up Linux Postfix Courier SquirrelMail Mail Server

Jacob — Mon, 18 Oct 2004 06:49:16 +0000

IDEAlog.us – Helpful guide to setting up Linux Debian Postfix Courier SquirrelMail Mail Server

I plan to read this some day. Its about how to set up a web based (maybe also Imap) mail server for cheep. It might be useful in what I want to do someday with peargrove communications.

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What NOT to put on a resume

Jacob — Tue, 21 Sep 2004 06:15:53 +0000

We are hiring new people at the computer support office in the Chemistry Department and I was looking through resumes decided who we might want to hire.

One person listed languages he knew, which included pascal. I didn’t know anyone knew pascal any longer. Certainly, no one uses it. Why then clutter a resume with it? Its not like its that impressive.

Another person had a cover letter which said something about “applying for.” Thats right, it just gave a period instead of listing the position. It was obviously a fill in the blank situation, because we got another resume from the same guy that was exactly the same except the position had been put in.

Since when was Microsoft Windows a skill? At least that is what I thought, until I realized that I’ve been using Linux for so long that I have forgotten how to configure or efficiently support a Windows platform.

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