Outreachy - end of week 2 report

I was working on my first task - adding support to image dimensions that are not multiple of 8.
I first thought it shouldn't take more than few days, but it turned out to be more complicated than I thought. It took me some time to understand the exact requirement and how the API should work.
Then after I more or less understood what I should do, I had a lot of bugs related to implementing the padding.
The task involved adding code to the kernel both for the encoder and the decoder and then updating the userspace to use to new API. Both userspace and kernel space had changes in the encoder side and decoder side. This made it a bit hard to debug since when the output video looked bad, that means the bug could be hidden in any of the 4 components. So trekking bugs took a while.
For testing I used a fascinating video showing jellyfish moving in the water.
It can be downloaded here.
And here are some screenshots.

I wrote some utilities to help me debug. One utility  gives a value of a pixel in a yuv420 video for a given tuple (frame,plane,row,column). Other utility that helped a lot is a code that separates a yuv420 video to 3 separate videos - one for each plane. This is very helpful for understanding which of the 3 planes was defected.
Here are the utilities code: first and second (both compiled with gcc without any special flags).
Here are examples of how to use:

dafna@ubuntu:~/out2$ ./get_pix_in_yuv420 images/jelly-1920-1080.YU12 1920 1080 b 5 4 1000
the value in plane 'b', frame 5, raw 4 col 1000 is 134 (0x86)

dafna@ubuntu:~/out2$ ./split_yuv420_planes images/jelly-1920-1080.YU12 1920 1080 y.grey u.grey v.grey
reading frame 0
dafna@ubuntu:~/out2$ ffplay -v info -f rawvideo -pixel_format gray -video_size 1920x1080  y.grey

Apparently the word "gray" can be spelled with either "e" or "a", depends on whether you come from UK or USA. 

Those utilities with a combination of a pile of debugs prints in the kernel and v4l-utils helped me understand where the bugs reside.

Here are some unpleasant surprises I got during my work:

After fixing the code I sent two patches, one for the kernel and one for v4l-utils. Now I am in a phase of re sending the patches after review.

Starting the Outreachy internship

I am starting my outreachy internship officially tomorrow.
During my intern I will demonstrate the statefull and stateless APIs for implementing codecs in the media subsystem of the Linux Kernel.
There are 2 new APIs that media drivers such as codecs, webcams and so on should implement.
In order to test and demonstrate the APIs, two testing drivers where implemented: vivid and vicodec.
Also a userspace library v4l-utils implements the API from the userspace side.
I will mainly add API functionally to the vicodec codec.
This blog is a report of my internship.It will be mainly technical.

My mentors are Helen Koike and Hans Verkuil, we already chat and had a video meeting and they were both really great and helping, thanks:)

I am pretty excited and also kind of worried for not accomplishing enough or not do things good enough.
The outreachy is a full-time commitment for 3 month working from home.
Working from home is both fun but also challenging - I have to decide for my own schedule, resist tempting time wasters such as facebook etc and be my own boss for better and worse.
Another issue with working from home is the social isolation - no one to lunch with, no one for coffee break... Just me and the passive-aggressive neighbors cat.

During the contribution phase I did a lot of preparations:

- Prepping cleanup patches for staging drivers in the kernel: this is a bit tedious procedure that teaches how to work with git and send patches. It is defiantly a very good preparation for the understanding how the kernel community works and how to work with it.
The patches are sent to the outreachy-kernel group: https://groups.google.com/forum/#!forum/outreachy-kernel
It is view by Julia Lawall and Vaishali Thakkar which gives comments on the patches and are very responsive and willing to help. Thank you:)

- I bought a new computer after 6 years with an old Dell Insperion , I decided to buy a new Leptop. So I bought a Thinkpad P52s. Preparing the new computer took quite a time.
I installed xubuntu which is an Ubuntu but nicer :) . Then I figured out some nvidia drivers are missing and it used a driver "nouveau" that kept crashing. So I had to reboot my leptop each time it crashed until I figured out how to remove it.

- Then after all the installation and configurations that I like I installed a vm. I started with installing the compiled kernels on my hard machine but this is not a good idea, the whole computer becomes a guinea pig and should be rebooted on Oops (kernel modules crash). So I installed a regular Ubuntu as a vmware VM and I compiled and installed my kernel there.

- One more thing that occupied my conscious is the IDE - I used to program with emacs, but I never bothered to learn all the extension to emacs , so I never really used it as an IDE. The kernel code is huge and it is hard to work with without and IDE. I was wandering if I should use one of many IDEs out there or should I use vim. I decided to move to vim as it seems more used by kernel developers. Learning vim is a projects by itself. It is still a mystery how it became so popular. I will probably post some vim tips in this blog as well.

By the way, English is a second language for me, so I am a bit limited with vocabulary and might have stupid grammar mistakes, sorry.

Thanks a lot for the outreachy organizers and organization. Bringing more people from different cultures and genders from around the world to FOSS is really great.