Date: Thu, 9 Apr 2009 15:04:37 -0400 (EDT) From: Rick Macklem <rmacklem@uoguelph.ca> To: freebsd-fs@freebsd.org Subject: integrating nfsv4 locking with nlm and local locking Message-ID: <Pine.GSO.4.63.0904091433590.24215@muncher.cs.uoguelph.ca>
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My nfsv4 server currently does VOP_ADVLOCK() with the non-blocking F_SETLK type and I had thought that was sufficient, but I now realize (thanks to a recent post by Zachary Loafman) that this breaks when a delegation for the file is issued to a client. (When a delegation for a file is issued to a client, it can do byte range locking locally, and the server doesn't know about these to do VOP_ADVLOCK() on the server machine.) I believe that Zachary would like to discuss a more general solution, including how to handle Open/Share locks, but in the meantime I'd like to solve this specific case in as simple a way as possible. Basically, I need a way to make sure delegations for a file don't exist when local byte range locking or locking via the NLM is being done on the file. The simplest thing I can think of is the following: When VOP_ADVLOCK() is called for a file (outside of the nfsv4 server), do two things: 1 - Make sure any outstanding delegations are recalled. I already have a function that does this, so it is a matter of figuring out where to put the call(s). 2 - Set a flag on the vnode, so that my nfsv4 server knows not to issue another delegation for that file. (I could test for locks via VOP_ADVLOCK() before issuing a delegation, but that has two problems.) 1 - Since the vnode is unlocked for VOP_ADVLOCK(), there could be a race where the nfsv4 server issues a delegation between the time outstanding delegations are recalled at #1 above and the VOP_ADVLOCK() sets the lock that I would see during the test. 2 - It would have to keep checking for a lock and might issue a delegation at a point where no lock is held, but one will be acquired soon, forcing the delegation recall. (It's much easier to not issue a delegation than recall one.) Once this flag is set, I think it would be ok if the flag remains set until the vnode is recycled, since it seems fairly likely that, once byte range locking is done on a file, more will happen. (If people were agreeable to the vnode flag, it looks like a VV_xxx flag would make more sense than a VI_xxx one. I think an atomic_set_int() would be sufficient to set it, even though the vnode lock isn't held?) So, how does this sound? rick
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