[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, 7 insertions, 0 deletions

diff --git a/fs/cifs/cifspdu.h b/fs/cifs/cifspdu.h
index b4e2e9f0..eda6e51 100644
--- a/fs/cifs/cifspdu.h
+++ b/fs/cifs/cifspdu.h
@@ -43,6 +43,7 @@
 #define SMB_COM_CREATE_DIRECTORY      0x00 /* trivial response */
 #define SMB_COM_DELETE_DIRECTORY      0x01 /* trivial response */
 #define SMB_COM_CLOSE                 0x04 /* triv req/rsp, timestamp ignored */
+#define SMB_COM_FLUSH                 0x05 /* triv req/rsp */
 #define SMB_COM_DELETE                0x06 /* trivial response */
 #define SMB_COM_RENAME                0x07 /* trivial response */
 #define SMB_COM_QUERY_INFORMATION     0x08 /* aka getattr */
@@ -790,6 +791,12 @@ typedef struct smb_com_close_rsp {
 	__u16 ByteCount;	/* bct = 0 */
 } __attribute__((packed)) CLOSE_RSP;
 
+typedef struct smb_com_flush_req {
+	struct smb_hdr hdr;	/* wct = 1 */
+	__u16 FileID;
+	__u16 ByteCount;	/* 0 */
+} __attribute__((packed)) FLUSH_REQ;
+
 typedef struct smb_com_findclose_req {
 	struct smb_hdr hdr; /* wct = 1 */
 	__u16 FileID;