I need to patch the my.cnf file that is part of the mysql/mariadb recipe. It lives in meta-openembedded/meta-oe/recipes-support/mysql/mariadb/my.cnf with the mariadb_5.5.52.bb file one level down.

I've set up a mariadb_5.5.52.bbappend file as:

FILESEXTRAPATHS_prepend := "${FILE_DIRNAME}/${PN}:"

SRC_URI += "file://my.cnf.patch"

# need to enable auto startup
SYSTEMD_AUTO_ENABLE_${PN}-server = "enable"

bitbake finds the my.cnf.patch file but reports that it can't find the my.cnf file to patch. I've set up patching of files that are downloaded as part of a source tree, but never tried to patch a file that is part of a recipe, and apparently I'm missing something. Is it possible to do this, and if so, can someone point out what I need to do to do it correctly?