Xen bus_dma Grant Table Handler

Starts

Ends

Description

Comments

Status

May 15

May 30

Preparation work, community bonding, create wiki page, setup accounts and working environment, read FreeBSD coding guidelines, checked-out the FreeBSD code

This activity took time because I couldn’t setup suitable coding environment for myself. Since I did not download the GUI for FreeBSD, so I maintained two working environments, one for coding which is Ubuntu (preferred) and another for testing which is FreeBSD so, had to run OS on virtual machine. Therefore, it took time to setup right environment for myself suiting my needs.

May 30

June 20

FreeBSD code walkthrough (bus_dma, grant table), OpenBSD code walkthrough (xen.c), understanding virtualization, Xen, device drivers, debugging kernel, understanding code APIs - https://www.freebsd.org/cgi/man.cgi?query=busdma&sektion=9

During this period, the biggest challenge was to understand the technical terms used in the literature [1], [2] and their relevance implementation wise [1]. For example, [1] directly talks about functions and data structures, which I had no idea. Before beginning the project, I tried to enhance my understanding on key concepts like virtualization [6], hypervisor [6], Xen [6], Xenstore [6]. After the above exercise, I could comprehend the terms used in the codebase and be able to relate the code’s functionality through comments. The [1] helped me in understanding the sys/dev/pv/xen.c in OpenBSD. When I looked at FreeBSD code the issue was what files to look at. I started with few random files with xen and bus_dma in its name or code. [5] and xen.c of OpenBSD helped me structuring my understanding of code flow, some trivial APIs and data structures common across BSD OS. After confirming from my mentor, now, I had identified the area I need to work on. I mapped the common functions like _bus_dmamap_*, referred [1] and started discovering the code. For grant table, I used the predefined FreeBSD APIs and didn’t create my own as in OpenBSD. Note: Numbers in the bracket represents the order number of the like in the useful link section below.

June 20

June 26

First prototype of integration of grant table into bus_dma(9) and seek improvements to make it a part of the first deliverable

In this period, I also designed several prototypes and tried to solve the problem in numerous ways. I crashed Kernel several times, even stuck in between because the idea required more work or the required information is missing and need to store it in some data structure. I debugged [7] the code only when it crashed to find its cause. By this time, I knew every small thing about the code I was working on and what was talked in [1] and [2].

June 26

June 30

First deliverable to be delivered

I have delivered a small implementation of the project. My changes are limited to the busdma_bounce.c. I am able to store grant table references, assign them to the DMA maps, loading them and then destroying them. My implementation is similar to what it is done in OpenBSD but I have more ideas around implementation. I would be planning to extend it to other areas of code using bus_dma(9).

June 30

July 20

Resume coding and integrate the functionality to all frontends and backends

July 20

July 24

Stress testing, bugs removal, further enhancements, and code review

July 24

July 28

Second deliverable to be delivered

July 28

August 21

Documentation, code review, comments incorporation, performance improvements, testing, and bugs removal