I have a project which is using yocto for building libraries including gstreamer. I found out that I need to patch some gstreamer element thus creating new bitbake recipe with patch..
I usually have to run bitbake with image name as parameter which will rebuild whole yocto (which is quite long):
MACHINE=some_machine nice bitbake yocto-etc-etc
How do I rebuild just that part which I need and not whole yocto? I heard about devtool, but I am not sure how to use that.
Certainly, this is easy to do. Just specify the recipe you want to build instead of the image name, for example if it was the main gstreamer recipe you had changed (which at least in current versions is called gstreamer1.0):
MACHINE=some-machine bitbake gstreamer1.0
Note that the name expected on the command line is always a recipe name or something from PROVIDES in a recipe, and not a runtime package name.
Regarding devtool, it can certainly put you into an environment where you can more easily make changes to the source for a recipe and generate patches from them, but the actual building part we are discussing here doesn't really change. You can find more information on how to use devtool in the Yocto Project Development Manual