BSD license allows you to re-use fixes of others (assuming they also release their fix under BSD), but it does not compel them them to reveal their fix if they

BSD license allows you to re-use fixes of others (assuming they also release their fix under BSD), but it does not compel them them to reveal their fix if they distribute only a binary. GPLv2 requires modified public distributions to also be under GPLv2, so you could both see the fix/change and use it (in the sense that you won't be infringing on copyright). GPLv3 adds patent protection, so someone adding a fix/change that they have also patented explicitly grants a license for that patent. I think GPLv3 is the most comprehensive way to keep fixes/changes of others available for reuse.