[CIFS] Send SMB flush in cifs_fsync

In contrast to the now-obsolete smbfs, cifs does not send SMB_COM_FLUSH
in response to an explicit fsync(2) to guarantee that all volatile data
is written to stable storage on the server side, provided the server
honors the request (which, to my knowledge, is true for Windows and
Samba with 'strict sync' enabled).
This patch modifies the cifs_fsync implementation to restore the
fsync-behavior of smbfs by triggering SMB_COM_FLUSH after sending
outstanding data on the client side to the server.

Signed-off-by: Horst Reiterer <horst.reiterer@gmail.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
index 083dfc57c7a..596fc868937 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -281,6 +281,9 @@ extern int CIFSPOSIXCreate(const int xid, struct cifsTconInfo *tcon,
 extern int CIFSSMBClose(const int xid, struct cifsTconInfo *tcon,
                         const int smb_file_id);
 
+extern int CIFSSMBFlush(const int xid, struct cifsTconInfo *tcon,
+                        const int smb_file_id);
+
 extern int CIFSSMBRead(const int xid, struct cifsTconInfo *tcon,
                         const int netfid, unsigned int count,
                         const __u64 lseek, unsigned int *nbytes, char **buf,