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

[Rick Macklem]

Doug Rabson wrote:
> You could add a single integer-valued vfsopt which holds the
> high-order
> bits of f_flags?
> 
Yes, that sounds better than any of my ideas. I'll code up a patch
and put it up for review unless someone has a better solution.

Thanks Doug, rick

> On 7 May 2015 at 02:10, Rick Macklem <rmacklem at uoguelph.ca> wrote:
> 
> > David Boyd reported a problem to freebsd-current@ 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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