Conditional inclusion of patch file in recipe script

Question

I have recipe file and my SRC_URI section looks something as follows:

SRC_URI += "file://file1.patch \
            file://file2.patch \
            file://file4.patch \
           "

I want to include a file5.patch under the SRC_URI only if a certain environment variable is set. Is there a way to insert a if condition with the SRC_URI that looks something like this:

SRC_URI += "file://file1.patch \
            file://file2.patch \
            file://file4.patch \
            **if $ENVIRONMENT_VARIABLE:
               file://file5.patch**
           "

Is there any other way I can achieve the same thing?

Answer 1

Well, the short answer is: yes, you can do this, but it's messy and there's probably a Better Way(TM). So let's answer the question first. If you really want to change the behavior of a recipe using an environment variable, the first challenge is to set the environment variable, and then let bitbake know that your new environment variable is safe and allowable. When you source the oe-init-build-env script to setup your project or subsequently to setup your new shell to continue working on the project, it sets an env variable called BB_ENV_EXTRAWHITE. You must include your new env variable in this list like this:

$ export MYENV_VAR=file5.patch
$ export BB_ENV_EXTRAWHITE="$BB_ENV_EXTRAWHITE MYENV_VAR"

Once this is done, then bitbake won't scrub the environment of your new environment variable.

In your recipe, use a python snippet to conditionally add your patch as follows:

SRC_URI += "${@os.getenv('MYENV_VAR', '')}"

As you can see, it's a bit messy. Of course, you could get a little more complex and test the value of the variable in your recipe, instead of putting the name of the patch file in your environment variable, but this example was the simplest way to demonstrate the concept.

Perhaps a better way is to use an override, and not rely on environment variables. If you are building a bsp with multiple variants, you could use your bsp name as the override, something like this.

SRC_URI_append_mybsp = "file://file5.patch"

This is a much cleaner way to accomplish the same thing. Of course, I'm speculating about your use case. The yocto project reference manual explains overrides. One more suggestion, join #yocto or the yocto project mailing list and you will have access to many smart people to help you.

Hope this helps. ;)