Date: Sat, 12 Apr 2008 16:20:50 -1000 (HST) From: Jeff Roberson <jroberson@jroberson.net> To: Alfred Perlstein <alfred@freebsd.org> Cc: Kirk McKusick <mckusick@mckusick.com>, arch@freebsd.org Subject: Re: VOP_LEASE Message-ID: <20080412161417.Q43186@desktop> In-Reply-To: <20080413020855.GA95731@elvis.mu.org> References: <200804121703.m3CH3StJ081660@chez.mckusick.com> <41ED3941-E5E6-45F0-B880-C1B2861FDE32@rabson.org> <20080412131017.S43186@desktop> <20080412234547.GZ95731@elvis.mu.org> <20080412135135.V43186@desktop> <20080413020855.GA95731@elvis.mu.org>
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On Sat, 12 Apr 2008, Alfred Perlstein wrote: > * Jeff Roberson <jroberson@jroberson.net> [080412 16:51] wrote: >> >> On Sat, 12 Apr 2008, Alfred Perlstein wrote: >> >>> * Jeff Roberson <jroberson@jroberson.net> [080412 16:13] wrote: >>>> On Sat, 12 Apr 2008, Doug Rabson wrote: >>>> >>>>> >>>>> On 12 Apr 2008, at 18:03, Kirk McKusick wrote: >>>>> >>>>>>> Date: Sat, 12 Apr 2008 02:13:15 -1000 (HST) >>>>>>> From: Jeff Roberson <jroberson@jroberson.net> >>>>>>> To: arch@freebsd.org >>>>>>> Subject: VOP_LEASE >>>>>>> >>>>>>> As far as I can tell this has never been used. Unless someone can show >>>>>>> me >>>>>>> otherwise I'm going to go ahead and remove it. >>>>>>> >>>>>>> Thanks, >>>>>>> Jeff >>>>>> >>>>>> VOP_LEASE is used by NQNFS and NFSv4. It notifies them when a file >>>>>> is modified locally so that they know to update any outstanding >>>>>> leases (e.g., evict any write lease for the file and do callbacks >>>>>> for any read leases for the file). Deleting VOP_LEASE would break >>>>>> NFS big time. >>>>> >>>>> I think our NQNFS support might have been removed some time ago - I can't >>>>> see any calls to VOP_LEASE in the code right now. Something like >>>>> VOP_LEASE >>>>> would certainly be useful for a hypothetical future NFSv4 server. I >>>>> believe that samba could use it too for its oplocks feature which appears >>>>> to be similar to NQNFS's leases and NFSv4's delegations. >>>> >>>> So the idea with delegations is that close() doesn't actually release the >>>> file entirely to make future access cheaper? >>>> >>>> My issue with VOP_LEASE is only that there are no in kernel >>>> implementations of the VOP. I doubt it is applied regularly in syscalls. >>>> It also seems odd that it is called without a lock. >>>> >>>> Is the intent that the server will trap all accesses to a local vnode in >>>> order to invalidate the client leases? >>> >>> VOP_LEASE is supposed to implemented by a filesystem client. >>> >>> For insance, NFS client with NQNFS would implement the VOP_LEASE >>> and trap those accesses to manage the lease with the remote server. >>> >>> The remote server would get "lease RPCs" from the client and manage >>> the cache appropriately. So just to be clear, this is required for nfsv4 client but not presently used by nfsv4 client? The vnodes we're calling VOP_LEASE on are actually remote files? >> >> So why isn't this done within the actual VOP? If the lease expires >> between calling VOP_LEASE and vn_lock(), VOP_READ() you have to do that >> work all over again anyway. >> >> I don't yet see why this is in filesystem independent code. I'm not >> asserting that it doesn't need to be. I'd just like to understand it >> better. > > The reason to have it is to reduce code duplication and not to be > holding the vnode locks while doing the callbacks into the server > code. > > Let me explain, the reason is 2-fold, one for reducing code duplication > and the other for avoiding holding locks for extended periods. > > Consider a local client contending against a remote client for a > filesystem that supported leases. > > Basically, each and every filesytem would have to explicitly do a > VOP_LEASE at the start of every routine that required notifying the > server making use of the underlying filesystem. So this is for the _server_ side and not the client side. That's what I originally asked. So you want to notify the nfsv4 server code that has mounted a local filesystem that you're going to modify or read a file locally so it can invalidate the client cache. Correct? > > What you really wind up doing is having a vop_stdlocallease that > calls into a generic lease manager that does callbacks into any > server exporting that file. > > So, if you move the lease call INTO the VOP_READ/READDIR/WRITE/etc > you wind up holding vnode locks while doing client communication > when contending with remote servers. Ok but doesn't this open a race? What about: VOP_LEASE() -> invalidate current remote leases <- new lease established vn_lock() VOP_WRITE() vn_unlock() Jeff > > -- > - Alfred Perlstein >
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