This is the client VFS module for the Common Internet File System
(CIFS) protocol which is the successor to the Server Message Block
(SMB) protocol, the native file sharing mechanism for most early
PC operating systems. The CIFS protocol is fully supported by
file servers such as Windows 2000 (including Windows 2003, NT 4
and Windows XP) as well by Samba (which provides excellent CIFS
server support for Linux and many other operating systems). Limited
support for Windows ME and similar servers is provided as well.
You must use the smbfs client filesystem to access older SMB servers
such as OS/2 and DOS.

The intent of the cifs module is to provide an advanced
network file system client for mounting to CIFS compliant servers,
including support for dfs (hierarchical name space), secure per-user
session establishment, safe distributed caching (oplock), optional
packet signing, Unicode and other internationalization improvements,
and optional Winbind (nsswitch) integration. You do not need to enable
cifs if running only a (Samba) server. It is possible to enable both
smbfs and cifs (e.g. if you are using CIFS for accessing Windows 2003
and Samba 3 servers, and smbfs for accessing old servers). If you need
to mount to Samba or Windows from this machine, say Y.

source code:

fs/cifs/