BUG: Mount ignores mount options

[Andy Lutomirski]

> On Aug 10, 2018, at 7:05 AM, Eric W. Biederman <ebiederm at xmission.com> wrote:
> 
> 
> There is a serious problem with mount options today that fsopen does not
> address.  The problem is that mount options are ignored for block based
> filesystems, and any other type of filesystem that follows the same
> pattern.
> 

> /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.