On Sun, Dec 31, 2006 at 11:12:52AM +0100, Pavel Cahyna wrote:
> On Fri, Dec 29, 2006 at 04:34:45PM +0100, Juergen Hannken-Illjes wrote:
> > +/*
> > + * Lock the node.
> > + */
> > +int
> > +ufs_lock(void *v)
> > +{
> > +	struct vop_lock_args /* {
> > +		struct vnode *a_vp;
> > +		int a_flags;
> > +	} */ *ap = v;
> > +	struct vnode *vp = ap->a_vp;
> > +	struct mount *mp = vp->v_mount;
> > +
> > +	/*
> > +	 * Fake lock during file system suspension.
> > +	 */
> > +	if ((vp->v_type == VREG || vp->v_type == VDIR) &&
> > +	    fstrans_is_owner(mp) &&
> > +	    fstrans_getstate(mp) == fstrans_suspending) {
> > +		if ((ap->a_flags & LK_INTERLOCK) != 0)
> > +			simple_unlock(&vp->v_interlock);
> > +		return 0;
> 
> How is safe to "fake" a lock? If the caller wants to lock something, it
> probably does not expect the lock to be "faked".

Caller here is the thread running the suspension (fstrans_is_owner(mp)) while
it is preparing the suspension (fstrans_getstate(mp) == fstrans_suspending).
This is only the call to ffs_sync() in ffs_suspendctl().
ffs_sync() will release all locks it got so we will not break other locks.

> Why is it needed at all?

ffs_sync() and all operations it calls depend on locks. It would become an
ugly maze if we converted all these places to ignore locks while suspending.

-- 
Juergen Hannken-Illjes - hannken@eis.cs.tu-bs.de - TU Braunschweig (Germany)