Here's a little guide to working on OpenBMC. This document will always be a work-in-progress, feel free to propose changes.
Authors:
Jeremy Kerr jk@ozlabs.org
OpenBMC has quite a modular structure, consisting of small daemons with a limited set of responsibilities. These communicate over dbus with other components, to implement the complete BMC system.
The BMC's interfaces to the external world are typically through a separate daemon, which then translates those requests to dbus messages.
These separate projects are then compiled into the final system by the overall 'openbmc' build infrastructure.
For future development, keep this design in mind. Components' functionality should be logically grouped, and keep related parts together where it makes sense.
If you're starting out with OpenBMC, you may want to take a look at the issues tagged with 'bitesize'. These are fixes or enhancements that don't require extensive knowledge of the OpenBMC codebase, and are easier for a newcomer to start working with.
Check out that list here:
https://github.com/issues?utf8=%E2%9C%93&q=is%3Aopen+is%3Aissue+user%3Aopenbmc+label%3Abitesize
If you need further details on any of these issues, feel free to add comments.
Components of the OpenBMC sources should have consistent style.
For C code, we typically use the Linux coding style, which is documented at:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/CodingStyle
In short:
Indent with tabs instead of spaces, set at 8 columns
80-column lines
Opening braces on the end of a line, except for functions
We use git for almost everything. Changes should be sent as patches to their relevant source tree - or a git pull request for convenience.
Each commit should be a self-contained logical unit, and smaller patches are usually better. However, if there is no clear division, a larger patch is okay. During development, it can be useful to consider how your change can be submitted as logical units.
Commit messages are important. They should describe why the change is needed, and what effects it will have on the system. Do not describe the actual code change made by the patch; that's what the patch itself is for.
Use your full name for contributions, and include a "Signed-off-by" line, to indicate that you agree to the Developer's Certificate of Origin (see below).
Ensure that your patch doesn't change unrelated areas. Be careful of accidental whitespace changes - this makes review unnecessarily difficult.
The guidelines in the Linux kernel are very useful:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/SubmittingPatches
Your contribution will generally need to be reviewed before being accepted.
Code and commit messages should not refer to companies' internal documents or systems (including bug trackers). Other developers may not have access to these, making future maintenance difficult.
New dbus interfaces should be reusable
Type signatures should and use the simplest types possible, appropriate for the data passed. For example, don't pass numbers as ASCII strings.
New dbus interfaces should be documented in the 'docs' repository, at:
https://github.com/openbmc/docs/blob/master/dbus-interfaces.md
See also: http://dbus.freedesktop.org/doc/dbus-api-design.html
There are numerous resources avaialble elsewhere, but a few items that are relevant to OpenBMC work:
You almost never need to use system(<some shell pipeline>). Reading and writing from files should be done with the appropriate system calls.
Generally, it's much better to use fork(); execve() if you do need to spawn a process, especially if you need to provide variable arguments.
Use the stdint types (eg, uint32_t, int8_t) for data that needs to be a certain size. Use the PRIxx macros for printf, if necessary.
Don't assume that char is signed or unsigned.
Beware of endian considerations when reading to & writing from C types
Declare internal-only functions as static, declare read-only data as const where possble.
Ensure that your code compiles without warnings, especially for changes to the kernel.
By making a contribution to this project, I certify that:
(a) The contribution was created in whole or in part by me and I
have the right to submit it under the open source license
indicated in the file; or
(b) The contribution is based upon previous work that, to the best
of my knowledge, is covered under an appropriate open source
license and I have the right under that license to submit that
work with modifications, whether created in whole or in part
by me, under the same open source license (unless I am
permitted to submit under a different license), as indicated
in the file; or
(c) The contribution was provided directly to me by some other
person who certified (a), (b) or (c) and I have not modified
it.
(d) I understand and agree that this project and the contribution
are public and that a record of the contribution (including all
personal information I submit with it, including my sign-off) is
maintained indefinitely and may be redistributed consistent with
this project or the open source license(s) involved.