Category Archives: revision control

Teaching Python using a Caesar Cipher

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A Caesar cipher is a letter for letter exchange from a clear text to a encrypted text by shifting a set distance in the alphabet. Thus, if your set distance is 2, the letter A becomes C, the letter X becomes Z. To encrypt the last letters of the alphabet, you wrap around to the beginning, so Y becomes A and Z becomes B.

Caesar is commonly respelled to Ceasar, which I have done for this article. Use the spelling of your choice.

This is a fairly easy algorithm to code, and makes for a decent early class in python. Here are the steps I would go through to teach someone:

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Maintaining a change log in a git commit message

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Changes do not always get accepted upon initial submission. My current submission of the MCTP over PCC patch is at revision 37 and will likely have more. Previously, this patch was part of a series, and the change log was displayed in the series header email. However, now that I am down to a single patch, the change log should go in the email message with the patch attached.

It rturns out this is fairly simple to do: Puyt the change log at the =bottom of the commit message, after the Signed-Off-By tag. and after three dashes:

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Diff between Code review versions

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Bottom line up front: create a tag with each version of a code review you post, to be able to see changes between versions.

Git commits come in (at least) three flavors.

First is the personal flavor, where you commit to git in order to not lose some quantum of behavior you have just implemented. These commits are small, and may be breaking commits. They are not meant for upstream consumption in the long term.

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Getting a File from gitlab using a TOKEN

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I work on a system in our lab that I connect to via SSH. Fetching a file via the web and pushing it to this machine is quite slow, and I want to pull on this machine directly. The trick to make this work is to use a TOKEN from gitlab and oauth2 as the username portion of the URL. For example

curl -O   https://oauth2:$CI_JOB_TOKEN@gitlab.com/api/v4/projects/$PROJECT_ID/packages/generic/$PROJECT_NAME/$PROJECT_VERSION/$FILE

The CI_JOB_TOKEN must be set to a token that has appropriate permissions on your project. Most of the values I wrote as envvars could be copy-pasted from the gitlab packages link on the web.

Adding stable to a blobless clone

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We regularly sync various git repos from upstream to our company speicfic Linux repository. However, sometimes when working on a development machine, I need a branch from stable that we have not synced yet. If I did a blobless clone from our repository, doing a fetch from stable is going to pull over lots of blobs that I do not need.

Instead, I want to fetch just a specific tag. I can do this by adding the tag to the fetch command, and it will pull over only those blobs

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More Personal Ansible

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I can do anything. I can’t do everything. –Me

Anything worth doing is worth doing in a way you can check in to git. To recall what I did from the command line, I should turn those actions into a persist-able document. Do I? Not often enough. Often I rely on bash history to remind me of what I did last time. Since the machines I work on are out of a global pool, I have been burned by not recording commands before relinquishing a machine.

For complex series of tasks, it makes sense to execute a bash script to perform those tasks, and I have many of these. Shell scripting excels in doing command line tasks. Where it does not do so well is on tasks that are split over multiple machines. While curl is great for pulling and pushing files to webservers, the majority of my remote work requires ssh and scp to set things up. This is where Ansible comes in: If I can make a playbook that records the commands I use to perform that action, I can repeat it on another machine.

Here is what my workflow looks like as I try to get better at it:

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How not to waste time developing long-running processes

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Developing long running tasks might be my least favorite coding activity. I love writing and debugging code…I’d be crazy to be in this profession if I did not. But when a task takes long enough, your attention wanders and you get out of the zone.

Building the Linux Kernel takes time. Even checking the Linux Kernel out of git takes a non-trivial amount of time. The Ansible work I did back in the OpenStack days to build and tear down environments took a good bit of time as well. How do I keep from getting out of the zone while coding on these? It is hard, but here are some techniques.

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