The GVariant format string specifies that "u" -> guint32. We are storing (using the "u" character) some fields that are time_t, which is not guaranteed to be 32 bit (in some 64bit machines is 64bit while in some others is 32bit).

It should be safe to store time_t in guint32 variables as it will take a lot of years to overflow those 32bit integer.

Apart from that, looks like we can store the cache version as a guint16 instead of a guint32.