It seems both (IMAGE_INSTALL and CORE_IMAGE_EXTRA_INSTALL) can add packages into yocto image.
What's their difference?
I checked this issue:
Yocto: Difference between CORE_IMAGE_EXTRA_INSTALL and IMAGE_INSTALL
but I still don't understand what's their difference.
IMAGE_INSTALL is the variable that controls what is included in any image.
CORE_IMAGE_EXTRA_INSTALL is a convenience variable that enable you to add extra packages to an image based on the core-image class [1].
So if you're using an image based on core-image, adding something to CORE_IMAGE_EXTRA_INSTALL is just another way to add it to IMAGE_INSTALL. But if you're not using an image based on core-image, adding something to CORE_IMAGE_EXTRA_INSTALL does nothing.
Sometimes it's easy to make mistakes when adding something to IMAGE_INSTALL, like if you do IMAGE_INSTALL += "foo" from local.conf it would effectively replace the default lazy assignment done in core-image.bbclass resulting in a unbootable image. But doing CORE_IMAGE_EXTRA_INSTALL += "foo" in local.conf will not break, since it doesn't have essential content being set using lazy operators.
