On Sun, Dec 31, 2006 at 11:23:26AM +0100, Juergen Hannken-Illjes wrote:
> 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().

But how do you prevent ffs_sync from seeing inconsistent state?

> 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.

Why should it ignore lock while suspending instead of taking them
normally?