cifs: add function to get a tcon from cifs_sb

When we convert cifs to do multiple sessions per mount, we'll need more
than one tcon per superblock. At that point "cifs_sb->tcon" will make
no sense. Add a new accessor function that gets a tcon given a cifs_sb.
For now, it just returns cifs_sb->tcon. Later it'll do more.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/fscache.c b/fs/cifs/fscache.c
index 9f3f5c4..ec4318b0 100644
--- a/fs/cifs/fscache.c
+++ b/fs/cifs/fscache.c
@@ -66,11 +66,11 @@
 	if (cifsi->fscache)
 		return;
 
-	cifsi->fscache = fscache_acquire_cookie(cifs_sb->tcon->fscache,
+	cifsi->fscache = fscache_acquire_cookie(cifs_sb_tcon(cifs_sb)->fscache,
 				&cifs_fscache_inode_object_def,
 				cifsi);
 	cFYI(1, "CIFS: got FH cookie (0x%p/0x%p)",
-			cifs_sb->tcon->fscache, cifsi->fscache);
+			cifs_sb_tcon(cifs_sb)->fscache, cifsi->fscache);
 }
 
 void cifs_fscache_release_inode_cookie(struct inode *inode)
@@ -117,7 +117,8 @@
 		/* retire the current fscache cache and get a new one */
 		fscache_relinquish_cookie(cifsi->fscache, 1);
 
-		cifsi->fscache = fscache_acquire_cookie(cifs_sb->tcon->fscache,
+		cifsi->fscache = fscache_acquire_cookie(
+					cifs_sb_tcon(cifs_sb)->fscache,
 					&cifs_fscache_inode_object_def,
 					cifsi);
 		cFYI(1, "CIFS: new cookie 0x%p oldcookie 0x%p",