Comment 18 for bug 220658

The POSIX setting controls the wire protocol. Posix protocol makes filenames
case sensitive on the server side since that is where the name resolution takes place. The protocol setting is in fs/cifs/cifssmb.c:42 where the
protocol defs are enumerated.

The question here is what the default for CIFS should be because there are
compatibility implications for both. The default config from kernel.org is
to set POSIX and ATTR. What would break in Windows<->Linux interoperability if filenames became the UNIX/Linux default rather than the
Windows default?

My recommendation is to set them both because this is a client side setting.