[CIFS] work around bug in Samba server handling for posix open

Samba server (version 3.3.1 and earlier, and 3.2.8 and earlier) incorrectly
required the O_CREAT flag on posix open (even when a file was not being
created).  This disables posix open (create is still ok) after the first
attempt returns EINVAL (and logs an error, once, recommending that they
update their server).

Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/CHANGES b/fs/cifs/CHANGES
index b33c841..fc977df 100644
--- a/fs/cifs/CHANGES
+++ b/fs/cifs/CHANGES
@@ -11,6 +11,8 @@
 server disk (not just write it over the network).  Add new mount
 parameter to allow user to disable sending the (slow) SMB flush on
 fsync if desired (fsync still flushes all cached write data to the server).
+Posix file open support added (turned off after one attempt if server
+fails to support it properly, as with Samba server versions prior to 3.3.2)
 
 Version 1.56
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