[Desktop Action open]
Exec=/bin/true
Icon=unknown
Name=asdf
X-Ubuntu-Gettext-Domain=desktop_kdebase-workspace

[Desktop Entry]
Actions=open;
Type=Service
X-KDE-Action-Custom=true
X-KDE-Solid-Predicate=[ IS StorageVolume AND StorageVolume.ignored == false ]

21:58 < Torch> tdn: it goes to $HOME/.kde/share/apps/solid/$ACTIONNAME.desktop
21:59 < Torch> tdn: each time you modify it, you need to update the configuration cache by 
               running kbuildsycoca4 from a shell
21:59 < Torch> tdn: or the changes won't take effect