I initially asked about this on the mariadb-discuss list:
I've also submitted this as bug 74551 to Oracle:
If an includedir directive like the following is added to /etc/my.cnf:
MySQL should load any configuration variables from files in that directory if the file name ends with '.cnf' according to the documentation:
The problem I ran into is that MySQL appears to do the comparison based on the first dot character ('.') that appears in the filename. If I have a file with a full path like this:
MySQL appears to think that the extension of the file is '.6.cnf', rather than '.cnf', so it won't load configuration variables from it.
How to repeat:
Add an includedir directive to my.cnf.
In the directory named in the includedir directive, add a file with a name that adds in .cnf, but also has at least one additional dot character ('.') in the name.
Perform the comparison by seeing that the file name ends with '.cnf', rather than comparing against the string that appears after the first dot character ('.').