On Tue, Jun 01, 2010 at 11:44:03AM +0200, Juergen Hannken-Illjes wrote: > > It's not immediately clear how either of these ought to work, so > > I'm concerned that making the infrastructure less general will > > lead to problems. > > 1) One upper to many lower vnodes > This is a file system like unionfs. It has to lock either one or > many lower vnodes and does/will not earn anything of shared locks. > > 2) Many upper to one lower vnode > Such a layered file system could use a lock shared between ALL > upper and the lower vnode. Always taking the lower vnode's lock > will do the same. I see no need for shared locks here.
That seems plausible. > > In the long run I intend to make all the vnode ops symmetric with > > respect to locking, which should make a lot of this less toxic, but at > > the rate I've been able to work on this stuff we won't be there > > anytime soon. > > The asymmetry comes from functions like null_mount() where a vnode gets > locked by the lower layer and unlocked by the upper layer. A lower > layer expecting its VOP_LOCK() to be matched by a VOP_UNLOCK() will > fail badly. ...that is just broken, yes. If you can beat sanity into that, please do. -- David A. Holland dholl...@netbsd.org
