Can't start karaf using symbolic link

When using symbolic link, e.g.

root@foo:/usr/bin# ls -ls karaf
1 lrwxrwxrwx 1 root root 27 Jun 2 15:42 karaf -> /opt/opendaylight/bin/karaf

karaf fail to start because of wrong DIRNAME, as DIRNAME is based on $0 being the path of the executed file.
So in this case, DIRENAME=usr/bin, which doesn't work.

Karaf script is setting multiple env variable to be able to start correctly, and all of those variables are based on the KARAF_HOME, that is tied to the DIRNAME.