On Wed, 27 Nov 2002, Robert Watson wrote:

> On Thu, 28 Nov 2002, Bruce Evans wrote:
> > >
> > > > On Tue, 26 Nov 2002, Robert Watson wrote:
> > > >
> > > > Er, what is the mount(..., MNT_RELOAD ...) in tunefs for then?
> > >
> > > The problem is that some flags can't be changed via MNT_RELOAD and require
> > > a from-scratch mount.  I'm hoping that with nmount(), we can get a little
> > > more expressive regarding what changes are (and aren't) allowed to flags.
> > > Right now there's some uncomfortable masking.
> >
> > Why can't they be changed?  All the other tunefs flags except FS_ACLS
> > and FS_MULTILABEL are related to writing, so ffs_reload() has to support
> > them changing as a side effect of supporting transitions from read-only
> > to read-write mode.
>
> Switching ACLs to support a change shouldn't be a problem, although I'd
> generally discourage changing the ACLs flag very much, since you don't
> want inconsistent access control and other side effects of using ACLs
> inconsistently (they get out of sync, etc).  Multilabel can't be changed
> because of cache coherency issues: we cache label data in the vnode, and
> changing the origin of the label data (what MNT_MULTILABEL effectively
> does) would invalidate the contents of the cache.  To correct that, we'd
> have to support immediately (and atomically) walking the entire vnode list
> and re-loading and validating the labels, something that we don't
> currently do.

We should do this.  We already walk the vnode list and reload almost
everything else (cached file data and inode data).

Bruce


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