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Date:   Fri, 10 Aug 2018 16:24:08 +0100
From:   Al Viro <>
To:     Andy Lutomirski <>
Cc:     "Eric W. Biederman" <>,
        David Howells <>,
        John Johansen <>,
        Tejun Heo <>,,
        Paul Moore <>,
        Li Zefan <>,,,
        Casey Schaufler <>,,
        Greg Kroah-Hartman <>,
        Eric Biggers <>,,
        Tetsuo Handa <>,
        Johannes Weiner <>,
        Stephen Smalley <>,,,,,, "Theodore Y. Ts'o" <>,
        Miklos Szeredi <>
Subject: Re: BUG: Mount ignores mount options

On Fri, Aug 10, 2018 at 07:36:17AM -0700, Andy Lutomirski wrote:
> > On Aug 10, 2018, at 7:05 AM, Eric W. Biederman <> 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.

First of all, that does NOT belong anywhere other than fs itself.
Example: NFS.  Not every attempt to mount something leads to creation
of new fs instance; moreover, whether it will or not can't be predicted
in general.

PS: for pity sake, fix your MUA; 270-character lines are way over the

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