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From:   Miklos Szeredi <mszeredi@redhat.com>
Date:   Fri, 15 May 2020 15:04:02 +0200
Message-ID: <CAOssrKeNEdpY77xCWvPg-i4vQBoKLX3Y96gvf1kL7Pe29rmq_w@mail.gmail.com>
Subject: Re: Setting mount propagation type in new mount API
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc:     David Howells <dhowells@redhat.com>,
        lkml <linux-kernel@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        Petr Vorel <pvorel@suse.cz>,
        linux-man <linux-man@vger.kernel.org>
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On Fri, May 15, 2020 at 1:40 PM Michael Kerrisk (man-pages)
<mtk.manpages@gmail.com> wrote:
>
> Hello David, Miklos,
>
> I've been looking at the new mount API (fsopen(), fsconfig(),
> fsmount(), move_mount(), etc.) and among the details that remain
> mysterious to me is this: how does one set the propagation type
> (private/shared/slave/unbindable) of a new mount and change the
> propagation type of an existing mount?

Existing mount can be chaged with mount(NULL, path, NULL, MS_$(propflag), NULL).

To do that with a detached mount created by fsmount(2) the
"/proc/self/fd/$fd" trick can be used.

The plan was to introduce a mount_setattr(2) syscall, but that hasn't
happened yet...  I'm not sure we should be adding propagation flags to
fsmount(2), since that is a less generic mechanism than
mount_setattr(2) or just plain mount(2) as shown above.

Thanks,
Miklos