isofs: work-around for Rock Ridge+Joliet CDs with empty ISO root directory

If a CD has both Rock Ridge and Joliet extensions and the ISO root
directory is empty, no files are visible.  Disable Rock Ridge extensions
in this case and use Joliet root directory instead.
Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Guenter Roeck <guenter.roeck@ericsson.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/isofs/inode.c

@@ -543,6 +543,34 @@ static unsigned int isofs_get_last_session(struct super_block *sb, s32 session)
 	return vol_desc_start;
 }
 
+/*
+ * Check if root directory is empty (has less than 3 files).
+ *
+ * Used to detect broken CDs where ISO root directory is empty but Joliet root
+ * directory is OK. If such CD has Rock Ridge extensions, they will be disabled
+ * (and Joliet used instead) or else no files would be visible.
+ */
+static bool rootdir_empty(struct super_block *sb, unsigned long block)
+{
+	int offset = 0, files = 0, de_len;
+	struct iso_directory_record *de;
+	struct buffer_head *bh;
+
+	bh = sb_bread(sb, block);
+	if (!bh)
+		return true;
+	while (files < 3) {
+		de = (struct iso_directory_record *) (bh->b_data + offset);
+		de_len = *(unsigned char *) de;
+		if (de_len == 0)
+			break;
+		files++;
+		offset += de_len;
+	}
+	brelse(bh);
+	return files < 3;
+}
+
 /*
  * Initialize the superblock and read the root inode.
  *
@@ -842,6 +870,18 @@ static int isofs_fill_super(struct super_block *s, void *data, int silent)
 	if (IS_ERR(inode))
 		goto out_no_root;
 
+	/*
+	 * Fix for broken CDs with Rock Ridge and empty ISO root directory but
+	 * correct Joliet root directory.
+	 */
+	if (sbi->s_rock == 1 && joliet_level &&
+				rootdir_empty(s, sbi->s_firstdatazone)) {
+		printk(KERN_NOTICE
+			"ISOFS: primary root directory is empty. "
+			"Disabling Rock Ridge and switching to Joliet.");
+		sbi->s_rock = 0;
+	}
+
 	/*
 	 * If this disk has both Rock Ridge and Joliet on it, then we
 	 * want to use Rock Ridge by default.  This can be overridden