[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, 1 insertions, 0 deletions

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index e004f6db5fc8..44ff94d37e18 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -254,6 +254,7 @@ struct cifsTconInfo {
         atomic_t num_smbs_sent;
         atomic_t num_writes;
         atomic_t num_reads;
+        atomic_t num_flushes;
         atomic_t num_oplock_brks;
         atomic_t num_opens;
         atomic_t num_closes;