[CIFS] improve posix semantics of file create

Samba server added support for a new posix open/create/mkdir operation
a year or so ago, and we added support to cifs for mkdir to use it,
but had not added the corresponding code to file create.

The following patch helps improve the performance of the cifs create
path (to Samba and servers which support the cifs posix protocol
extensions).  Using Connectathon basic test1, with 2000 files, the
performance improved about 15%, and also helped reduce network traffic
(17% fewer SMBs sent over the wire) due to saving a network round trip
for the SetPathInfo on every file create.

It should also help the semantics (and probably the performance) of
write (e.g. when posix byte range locks are on the file) on file
handles opened with posix create, and adds support for a few flags
which would have to be ignored otherwise.
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/CHANGES

@@ -8,7 +8,9 @@ top of the share.  Fix problem in 2.6.28 resolving DFS paths to
 Samba servers (worked to Windows).  Fix rmdir so that pending search
 (readdir) requests do not get invalid results which include the now
 removed directory.  Fix oops in cifs_dfs_ref.c when prefixpath is not reachable
-when using DFS.
+when using DFS.  Add better file create support to servers which support
+the CIFS POSIX protocol extensions (this adds support for new flags
+on create, and improves semantics for write of locked ranges).
 
 Version 1.55
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