My understanding is you should sign L30 if you are developing patches while on company time. That is, it's really the company that is contributing the code, and not you. If you code on your free time only, then L28 is more appropriate. L30 might also cover the entire company contributing, maybe @epriestley can clarify.

@chad's answer is a good summary.

If you performed work in the course of your job and were compensated for it (with salary and benefits), there is a significant chance do not own that work. Because you do not own it, you can not legally grant us rights to it.

L28 covers cases where an individual owns the work (usually: they produced it on their own time, without compensation, and did not use company resources owned by their employer).

L30 covers cases where a company owns the work (usually: the company paid an employee to produce the work, or the employee used company resources to produce the work).

Broadly, my understanding is that, at least in the US, companies tend to have a strong claim of ownership on work you produce while employed there. Some companies strengthen this claim by explicitly including "invention assignment" or similar in employment agreements.

From a layman perspective, this generally makes sense if you're doing the work during the course of your normal responsibilities, since you're being paid to do that work. You get compensated with salary and benefits in exchange for the work, and the company owns the result of that work.

Even if you aren't doing the work during work hours, I believe there's significant precedent that companies can still make ownership claims against it if you used company resources (like a company laptop or phone or office space, or even "trade secrets" -- private information you know only because of your employment) to produce the work.

Your employment agreement may have additional requirements. For example, the last real job I had (Facebook, 2007) had employees sign a "Confidential Information and Invention Assignment Agreement" which basically says "you agree Facebook owns everything you produce as long as you're employed here, except where explicitly forbidden by the State of California".

Specifically, California Labor Code Section 2870 forbids total assignment, but that document still permits requiring assignment of a very large body of work -- anything that uses the "employer's equipment, supplies, facilities, or trade secret information".

Clause (4) in the individual CLA is covering us against this:

(4) You represent that you are legally entitled to grant the above license...

This is basically saying that you assert that you definitely own this work, and are entitled to give it to us.

If you were paid for it and work in the US, you probably do not own the work and likely can not legally grant us rights to it. I'm not familiar with the situation outside the US. I'm also not a lawyer, and may be wrong in my characterization of law in the US. Regardless, you should not contribute under L28 unless you are confident you can genuinely affirm clause (4).

If you work at a tech company in California, I would guess your employment agreement probably has a section similar to the one from Facebook's and that you are effectively governed by Section 2870. Again, I could be mistaken in this characterization. In this case, you probably can not contribute under L28 unless you are very careful to fully separate your contributions from your employer's resources.

In these cases, coordinate with your employer to authorize contributions under L30 instead.