On Wed, Jan 17, 2018 at 10:53:36AM +0100, Miklos Szeredi wrote:
> [Adding util-linux@vger and Michael Kerrisk]
>
> On Wed, Jan 17, 2018 at 5:17 AM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> > On Tue, Jan 16, 2018 at 05:41:46PM +0100, Miklos Szeredi wrote:
> >
> >> Right.
> >>
> >> Still, those two (propagation and flags) are properties of the mount.
> >> No fundamental difference in how to handle them, that I see. Okay, we
> >> have MS_REC handling in the propagation and not in the flags, but
> >> that's something that might make sense for flags as well.
> >>
> >> What's more interesting is how MS_PRIVATE + MS_REC semantics are
> >> complete failure in the real world: the logical thing would be to mark
> >> a mount private on the supplied mount AND propagate an umount event to
> >> everywhere else.
> >
> > This is utter nonsense. Most of the time it's "Fedora, in its infinite
> > bogo^Wwisdom has made everything shared; I don't fucking need that
> > idiocy, so please unshare this, this and that". You really don't want
> > (or have permissions for) unmounting e.g. /mnt in namespace of init
> > when you do that.
> >
> > Sure, we get tons of bug reports. Due to idiotic Fedora setup, with
> > everything shared. The same setup that would go up in flames on the
> > semantics change you propose.
I guess "all shared" is systemd requirement, so I guess it's not
Fedora specific, right?
> I wouldn't propose to change existing --make-private, as this would
> not be backward compatible. The new semantics would mean a new op,
> obviously.
Definitely.
> Documenting --make-private thing properly would also help. To me the
> wording "make private" strongly implies "I want to make submounts
> private to this instance". See for example rhbz#1432211.
All propagation stuff is poorly documented in mount.8. It would be
nice to add section about it to the man page. Volunteer? (My skills to
explain this topic to end-users is pretty limited...)
> > If anything, "private bind on itself" would be a useful operation.
> > Turning given location into a mountpoint, and having everything
> > under it looking as it used to, but with no propagation at all.
> > Without bothering anybody else, even if location currently happens
> > to be on a shared/master mount.
Good idea.
> > I can slap that together for mount(2), but I'm not sure what a sane
> > combination of flags for that would look like ;-)
What about new flag (for the API) rather than try to be smart with the
current flags? But I have doubts that invest time to new mount(2)
features is a good idea.
> For fsmount I think it would be very useful thing to have.
Yes.
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
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