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

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
> > > > _______________________________________________
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Rick, Edward, et al,

I have applied your patches to several (four) servers and have not
noticed any more instances of the errant behavior.

I think (hope) that this is the correct fix and wonder if this fix might
make it's way into an errata.

Thanks for the quick responses.

David Boyd.