linux-kernel - Re: [PATCH 06/14] VFS: Implement fsmount() to effect a pre-configured mount [ver #6]

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Date:   Tue, 10 Oct 2017 15:38:21 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     Karel Zak <kzak@...hat.com>
Cc:     David Howells <dhowells@...hat.com>,
        viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-nfs@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
        Jeff Layton <jlayton@...hat.com>
Subject: Re: [PATCH 06/14] VFS: Implement fsmount() to effect a pre-configured
 mount [ver #6]

On Tue, Oct 10, 2017 at 11:51 AM, Karel Zak <kzak@...hat.com> wrote:
> On Tue, Oct 10, 2017 at 10:00:01AM +0200, Miklos Szeredi wrote:
>> > +
>> > +       if (flags & MS_RDONLY)
>> > +               mnt_flags |= MNT_READONLY;
>> > +       if (flags & MS_NOSUID)
>> > +               mnt_flags |= MNT_NOSUID;
>> > +       if (flags & MS_NODEV)
>> > +               mnt_flags |= MNT_NODEV;
>> > +       if (flags & MS_NOEXEC)
>> > +               mnt_flags |= MNT_NOEXEC;
>> > +       if (flags & MS_NODIRATIME)
>> > +               mnt_flags |= MNT_NODIRATIME;
>> > +
>> > +       if (flags & MS_STRICTATIME) {
>> > +               if (flags & MS_NOATIME)
>> > +                       return -EINVAL;
>> > +       } else if (flags & MS_NOATIME) {
>> > +               mnt_flags |= MNT_NOATIME;
>> > +       } else {
>> > +               mnt_flags |= MNT_RELATIME;
>> > +       }
>>
>> I'm not sure reusing the MS_FLAGS is the right choice.  Why not export
>> MNT_* to userspace?  That would get us a clean namespace without
>> confusion with sb flags and no need to convert back and forth.
>
> Well, if you think about it as about two separated things -- VFS-flags
> and FS-flags (and for example /proc/#/mountinfo already uses two
> columns for the flags) than the question is why the API uses one
> variable?
>
> Would be better to use two variables everywhere? (mostly for the
> syscall).
>
> It would be nice to keep for example propagation flags only in
> vfs_flags, or use MS_RDONLY according to context (for FS or for VFS)
> without extra MS_BIND, etc.

MS_BIND will be gone in the new API.   The two separate columns in
/proc/#/mountinfo are going to be two separate things on the new
interface (one is writes to the fsfd provided by fsopen(2), the other
in flags for fsmount(2)).  The question is how to call the mount flags
(what you call vfs flags), "MS_RDONLY" or "MNT_RDONLY" on the uAPI.
Either is probably fine, but I feel that "MNT_FOO" is better, because
it's a relatively clean namespace concerned with mount flags and not
polluted with all the scum that mount(2) collected.

BTW, I think <linux-api@...r.kernel.org> should be CC-d on all patches
that concern the userspace API.

Thanks,
Miklos