What is the difference between PREMIRRORS and SOURCE_MIRROR_URL

Question

Yocto defines two variables: PREMIRRORS and SOURCE_MIRROR_URL for source mirroring.

What is the difference between both variables?

Answer 1

SOURCE_MIRROR_URL is used in own-mirrors.bbclass to populate PREMIRRORS. Thus, using SOURCE_MIRROR_URL and inherit += own-mirrors is just a shorthand to populate PREMIRRORS for all different fetchers (protocols).

See SOURCE_MIRROR_URL in the Yocto Project Reference Manual