if you have a case-insensitive XFS filesystem it's impossible to rename files case. Renaming a file fromm "APFEL" to "apfel" is impossible. For example a rename("APFEL", "apfel") returns 0 but the file is still UPPERCASE even though one would expect it to be lowercase when being ls'ed.
should this be reassigned to the VFS maintainers? There are also very ugly case-insensitivity bugs with cifs vfs, which look more like a kernel vfs issue than a filesystem problem. (also see https://bugzilla.samba.org/show_bug.cgi?id=9049)
I think this is actually as designed. APFEL==apfel so there is no need to actually make a change. The version=ci option enables ASCII only case-insensitive filename lookup and version 2 directories. Filenames are case-preserving, that is, the names are stored in directories using the case they were created with. -Eric