cifs: add cifs_sb_master_tcon and convert some callers to use it

At mount time, we'll always need to create a tcon that will serve as a
template for others that are associated with the mount. This tcon is
known as the "master" tcon.

In some cases, we'll need to use that tcon regardless of who's accessing
the mount. Add an accessor function for the master tcon and go ahead and
switch the appropriate places to use it.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
index f660a15..fe02435 100644
--- a/fs/cifs/dir.c
+++ b/fs/cifs/dir.c
@@ -54,18 +54,18 @@
 	int dfsplen;
 	char *full_path;
 	char dirsep;
-	struct cifs_sb_info *cifs_sb;
+	struct cifs_sb_info *cifs_sb = CIFS_SB(direntry->d_sb);
+	struct cifsTconInfo *tcon = cifs_sb_master_tcon(cifs_sb);
 
 	if (direntry == NULL)
 		return NULL;  /* not much we can do if dentry is freed and
 		we need to reopen the file after it was closed implicitly
 		when the server crashed */
 
-	cifs_sb = CIFS_SB(direntry->d_sb);
 	dirsep = CIFS_DIR_SEP(cifs_sb);
 	pplen = cifs_sb->prepathlen;
-	if (cifs_sb_tcon(cifs_sb) && (cifs_sb_tcon(cifs_sb)->Flags & SMB_SHARE_IS_IN_DFS))
-		dfsplen = strnlen(cifs_sb_tcon(cifs_sb)->treeName, MAX_TREE_SIZE + 1);
+	if (tcon->Flags & SMB_SHARE_IS_IN_DFS)
+		dfsplen = strnlen(tcon->treeName, MAX_TREE_SIZE + 1);
 	else
 		dfsplen = 0;
 cifs_bp_rename_retry:
@@ -117,7 +117,7 @@
 	/* BB test paths to Windows with '/' in the midst of prepath */
 
 	if (dfsplen) {
-		strncpy(full_path, cifs_sb_tcon(cifs_sb)->treeName, dfsplen);
+		strncpy(full_path, tcon->treeName, dfsplen);
 		if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS) {
 			int i;
 			for (i = 0; i < dfsplen; i++) {