Hi, So took me a while to grok the context, and to understand why it was working for me, and broken on another machine... > I have read the context in [1]. It seems your tool has already used new > mount api to mount the hostfs. Yes, however, that's a default that's entirely transparent to the user. This is why I wasn't seeing the errors, depending on the machine I'm running this on, because the 'mount' tool either uses the old or new style and the user can never know. > It now rejects unknown mount options as > many other filesystems do regardless of its earlier behavior (which > treats any option as the root directory in hostfs). And that's clearly the root cause of this regression. You can't even argue it's not a regression, because before cd140ce9f611 ("hostfs: convert hostfs to use the new mount API") it still worked with the new fsconfig() API, but with the old mount options... > I'm not sure it is reasonable in this way. If we accept unknown option > in the hostfs, it will be treated as root directory. But which one > should be used (like mount -t hostfs -o unknown,/root/directory none > /mnt). So in the conversion, we introduce the `hostfs` key to mark the > root directory. May be we need more discussion about use case. There's only one option anyway, so I'd think we just need to fix this and not require the hostfs= key. Perhaps if and only if it starts with hostfs= we can treat it as a key, otherwise treat it all as a dir? But I guess the API wouldn't make that easy. Anyway, I dunno, but it seems like a regression to me and we should try to find a way to fix it. johannes