Andy Lutomirski [off-list ref] wrote:

quoted

/dev/loop0 /root/loop0-noacl-noquota-nouser_xattr ext4 rw,relatime,nouser_xattr,noacl 0 0
/dev/loop0 /root/loop0-acl-quota-user_xattr ext4 rw,relatime,nouser_xattr,noacl 0 0

To make sure I understand correctly: the problem is that the second mount
ignored the options because the device was already mounted, right?

For the new API, I think the only remotely sane approach is to refuse to
mount or init or whatever you call it an already mounted bdev. If user code
genuinely needs to bind-mount an existing mount that is known only by its
bdev, we can add a specific API just for that.

I'm adding some flags to fsopen() to allow userspace to say whether it wants
no sharing, same parameters-only sharing or anything-goes sharing (as now).

I'm also adding a flag whereby userspace can forbid anyone else from sharing a
new superblock it has just set up.

David