cifs: add refcounted and timestamped container for holding tcons

Eventually, we'll need to track the use of tcons on a per-sb basis, so that
we know when it's ok to tear them down. Begin this conversion by adding a
new "tcon_link" struct and accessors that get it. For now, the core data
structures are untouched -- cifs_sb still just points to a single tcon and
the pointers are just cast to deal with the accessor functions. A later
patch will flesh this out.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/file.c

@@ -224,6 +224,7 @@ int cifs_open(struct inode *inode, struct file *file)
 	__u32 oplock;
 	struct cifs_sb_info *cifs_sb;
 	struct cifsTconInfo *tcon;
+	struct tcon_link *tlink;
 	struct cifsFileInfo *pCifsFile = NULL;
 	struct cifsInodeInfo *pCifsInode;
 	char *full_path = NULL;
@@ -235,7 +236,12 @@ int cifs_open(struct inode *inode, struct file *file)
 	xid = GetXid();
 
 	cifs_sb = CIFS_SB(inode->i_sb);
-	tcon = cifs_sb_tcon(cifs_sb);
+	tlink = cifs_sb_tlink(cifs_sb);
+	if (IS_ERR(tlink)) {
+		FreeXid(xid);
+		return PTR_ERR(tlink);
+	}
+	tcon = tlink_tcon(tlink);
 
 	pCifsInode = CIFS_I(file->f_path.dentry->d_inode);
 
@@ -402,6 +408,7 @@ out:
 	kfree(buf);
 	kfree(full_path);
 	FreeXid(xid);
+	cifs_put_tlink(tlink);
 	return rc;
 }