Re: nmount, mountd drops high order MNT_xx flags during a mount update

David Boyd wrote:
> On Sun, 2015-05-10 at 09:07 -0400, Rick Macklem wrote:
> > Oops, I did my usual and forgot to attach the patch.
> > 
> > Here it is, rick
> > 
> > ----- Original Message -----
> > > Doug Rabson wrote:
> > > > You could add a single integer-valued vfsopt which holds the
> > > > high-order
> > > > bits of f_flags?
> > > > 
> > > I have created a patch that does this. It is on
> > >   https://reviews.freebsd.org/D2506
> > > (I have also attached it here, for those who don't use
> > > Phabricator.)
> > > 
> > > Please review/comment on this. (Feel free to add yourself as a
> > > reviewer, etc.)
> > > 
> > > Also, David, if you can test this patch, it would be appreciated.
> > > 
> > > Thanks for the suggestion Doug, rick
> > > 
> > > > On 7 May 2015 at 02:10, Rick Macklem <rmacklem_at_uoguelph.ca>
> > > > wrote:
> > > > 
> > > > > David Boyd reported a problem to freebsd-current_at_ w.r.t. the
> > > > > MNT_AUTOMOUNTED
> > > > > flag getting cleared by mountd.
> > > > >   http://docs.FreeBSD.org/cgi/mid.cgi?1429477202.29812.38.camel
> > > > > I just took a look at this and it's kinda ugly...
> > > > >
> > > > > mountd acquires a list of mounts via getmntinfo() and then
> > > > > does
> > > > > an
> > > > > nmount() for each of them to get rid of any exports. It uses
> > > > > f_flags from the statfs returned by getmntinfo() as the 3rd
> > > > > argument to nmount().
> > > > > --> Since nmount()s 3rd argument is a "int", it silently
> > > > > drops
> > > > > any
> > > > >     MNT_xx flag in the high order 32bits of f_flags. At this
> > > > >     time,
> > > > >     it happens that MNT_AUTOMOUNTED is the only one, but...
> > > > >
> > > > > I can think of a couple of ways to fix this, but I don't like
> > > > > any
> > > > > of
> > > > > them;-)
> > > > >
> > > > > 1) I suppose mountd could check for each flag set in f_flags
> > > > > and
> > > > > generate
> > > > > a vfsopts string for it, but that means that every time a new
> > > > > flag
> > > > > that
> > > > > can be updated is added to MNT_xx, this mountd.c code would
> > > > > have
> > > > > to
> > > > > updated.
> > > > > --> Ugly!!
> > > > >
> > > > > 2) Require that all flags in MNT_UPDATEMASK be in the low
> > > > > order
> > > > > 32bits.
> > > > >    I wouldn`t mind this except in means that the MNT_xx flags
> > > > >    must
> > > > >    be
> > > > > redefined
> > > > >    and I don`t think that could get MFC`d.
> > > > >
> > > > > 3) Add a new newernmount(2) which has a 64bit flags argument
> > > > > instead of
> > > > > int.
> > > > >
> > > > > Hopefully someone can think of a nice way to fix this, rick
> > > > > _______________________________________________
> > > > > freebsd-current_at_freebsd.org mailing list
> > > > > http://lists.freebsd.org/mailman/listinfo/freebsd-current
> > > > > To unsubscribe, send any mail to
> > > > > "freebsd-current-unsubscribe_at_freebsd.org"
> > > > >
> > > > _______________________________________________
> > > > freebsd-current_at_freebsd.org mailing list
> > > > http://lists.freebsd.org/mailman/listinfo/freebsd-current
> > > > To unsubscribe, send any mail to
> > > > "freebsd-current-unsubscribe_at_freebsd.org"
> > > > 
> > > _______________________________________________
> > > freebsd-current_at_freebsd.org mailing list
> > > http://lists.freebsd.org/mailman/listinfo/freebsd-current
> > > To unsubscribe, send any mail to
> > > "freebsd-current-unsubscribe_at_freebsd.org"
> > > 
> > _______________________________________________
> > freebsd-current_at_freebsd.org mailing list
> > http://lists.freebsd.org/mailman/listinfo/freebsd-current
> > To unsubscribe, send any mail to
> > "freebsd-current-unsubscribe_at_freebsd.org"
> 
> Rick, Edward, et al,
> 
> I have applied your patches to several (four) servers and have not
> noticed any more instances of the errant behavior.
> 
Thanks for testing it and confirming that the problem is what I
thought it was.

> I think (hope) that this is the correct fix and wonder if this fix
> might
> make it's way into an errata.
> 
Well, at this point, it isn't obvious if it should even go in head/current.
(See https://reviews.freebsd.org/D2506)

The patch already in head/current (r281699) should fix your problem.
(It stops mountd from updating non-exported mounts.)
It has not been MFC'd, but I will look into that.
I don't know if it could also be an errata. Since it now appears to
be a fix for an observed bug and not just an optimization, maybe?

rick

> Thanks for the quick responses.
> 
> David Boyd.
> 
> _______________________________________________
> freebsd-current_at_freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-current
> To unsubscribe, send any mail to
> "freebsd-current-unsubscribe_at_freebsd.org"
>