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

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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