On systems with SELinux enabled, we have to create the directories on
top of which we mount another partition or virtual file system (e.g.,
/dev) with the correct SELinux context, BEFORE we mount the other
partition. Otherwise, SELinux will get really confused when systemd
tries to recreate the mount tree for a private file system namespace for
a service. And unfortunately, even an autorelabel does not fix it
because it runs when /dev etc. are already mounted.
Without this fix, on Fedora >= 30, the system installed with Calamares
would fail to start the dbus-broker system bus, leading to several
important pieces of functionality not working (e.g., shutdown as
non-root).
On systems without SELinux enabled, chcon (which is part of coreutils)
will just print a warning and do nothing, so this should always be safe.
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