debugfs: continue to ignore unknown mount options

Wolfram reported that debugfs remained empty on some of his boards
triggering the message "debugfs: Unknown parameter 'auto'".

The root of the issue is that we ignored unknown mount options in the
old mount api but we started rejecting unknown mount options in the new
mount api. Continue to ignore unknown mount options to not regress
userspace.

Fixes: a20971c1 ("vfs: Convert debugfs to use the new mount API")
Link: https://lore.kernel.org/r/20240527100618.np2wqiw5mz7as3vk@ninjatoReported-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/debugfs/inode.c

@@ -107,8 +107,16 @@ static int debugfs_parse_param(struct fs_context *fc, struct fs_parameter *param
 	int opt;
 
 	opt = fs_parse(fc, debugfs_param_specs, param, &result);
-	if (opt < 0)
+	if (opt < 0) {
+		/*
+                * We might like to report bad mount options here; but
+                * traditionally debugfs has ignored all mount options
+                */
+		if (opt == -ENOPARAM)
+			return 0;
+
 		return opt;
+	}
 
 	switch (opt) {
 	case Opt_uid: