BUG: Mount ignores mount options

[Eric W. Biederman]

Andy Lutomirski <luto at amacapital.net> writes:

>> 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?

Yes.

> 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.

Eric