Re: [PATCH] Make udf(4) MPSAFE and use shared lookups

On Thursday 20 November 2008 05:33:20 pm Attilio Rao wrote:
> 2008/11/20, John Baldwin <jhb_at_freebsd.org>:
> > On Thursday 20 November 2008 05:02:29 pm Attilio Rao wrote:
> >  > 2008/11/20, John Baldwin <jhb_at_freebsd.org>:
> >  > > So this patch is fairly minimal since udf(4) is currently read-only.  
The
> >  > >  changes include:
> >  > >
> >  > >  * Set VV_ROOT in udf_vget() if we ever return a vnode instead of 
doing it
> >  only
> >  > >   in udf_root().  This matches the behavior of other operating 
systems and
> >  > >   correctly tags the root vnode with VV_ROOT in the unlikely case 
that we
> >  > >   create the vnode during a call to ufs_vget() that does not come 
from
> >  > >   ufs_root().
> >  > >  * If the hash lookup in ufs_vget() fails, ensure an exclusive vnode 
lock
> >  is
> >  > >   used while creating the new vnode (same as UFS).
> >  > >  * Allow lock recursion (XXX: not really sure this is needed 
actually).
> >  > >  * Allow shared vnode locks on non-fifos.
> >  > >  * Honor the requested locking flags (shared vs exclusive) instead of
> >  always
> >  > >   using exclusive vnode locks during a lookup operation.
> >  > >  * Handle "." lookups the same way other filesystems do by just 
bumping
> >  the
> >  > >   reference on 'dvp' rather than calling udf_vget().
> >  > >
> >  > >  http://www.FreeBSD.org/~jhb/patches/udf_mpsafe.patch
> >  >
> >  > _at__at_ -589,6 +582,22 _at__at_
> >  >       if (error || *vpp != NULL)
> >  >               return (error);
> >  >
> >  > +     /*
> >  > +      * We must promote to an exclusive lock for vnode creation.  This
> >  > +      * can happen if lookup is passed LOCKSHARED.
> >  > +      */
> >  > +     if ((flags & LK_TYPE_MASK) == LK_SHARED) {
> >  > +             flags &= ~LK_TYPE_MASK;
> >  > +             flags |= LK_EXCLUSIVE;
> >  > +     }
> >  > +
> >  >
> >  > On -CURRENT, operations are bitwise (differently from 7.x and such).
> >  > What you want to do is just:
> >  > flag = (flag & ~LK_SHARED) | LK_EXCLUSIVE;
> >
> >
> > I just copied and pasted from UFS in HEAD.
> 
> Yeah, we could fix that also.

Although this code will likely be MFC'd to 7.x, so I'd rather do it in a 7.x 
friendly manner for now.

-- 
John Baldwin