[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/file.c b/fs/cifs/file.c
index 12bb656fbe75..83b4741b6ad0 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1523,6 +1523,9 @@ int cifs_fsync(struct file *file, struct dentry *dentry, int datasync)
 {
         int xid;
         int rc = 0;
+        struct cifsTconInfo *tcon;
+        struct cifsFileInfo *smbfile =
+                (struct cifsFileInfo *)file->private_data;
         struct inode *inode = file->f_path.dentry->d_inode;
 
         xid = GetXid();
@@ -1534,7 +1537,11 @@ int cifs_fsync(struct file *file, struct dentry *dentry, int datasync)
         if (rc == 0) {
                 rc = CIFS_I(inode)->write_behind_rc;
                 CIFS_I(inode)->write_behind_rc = 0;
+                tcon = CIFS_SB(inode->i_sb)->tcon;
+                if (!rc && tcon && smbfile)
+                        rc = CIFSSMBFlush(xid, tcon, smbfile->netfid);
         }
+
         FreeXid(xid);
         return rc;
 }