On Mon, May 17, 2010 at 08:33:52AM -0700, Matthew Fleming wrote: > > From: Kostik Belousov [mailto:kostik...@gmail.com] > > On Wed, May 12, 2010 at 09:24:46PM +0000, Zachary Loafman wrote: > > > Author: zml > > > Date: Wed May 12 21:24:46 2010 > > > New Revision: 208003 > > > URL: http://svn.freebsd.org/changeset/base/208003 > > > > > > Log: > > > Add VOP_ADVLOCKPURGE so that the file system is called when purging > > > locks (in the case where the VFS impl isn't using lf_*) > > > > > > Submitted by: Matthew Fleming <matthew.flem...@isilon.com> > > > Reviewed by: zml, dfr > > > > After looking at what happen to nullfs, see r208003, I wonder why > > the vop is needed. It is called after VOP_RECLAIM is called by vgonel(), > > after fs-specific data are destroyed. So, on the one hand, vop can only > > operate on struct vnode proper, on the other hand, the actions performed > > by vop_advlockpurge implementation can be done by vop_reclaim as well. > > > > Could you, please, give some details on the supposed use of the vop ? > > >From a design perspective, it makes little sense to allow overriding > the advlock operation, but not the purge. A specific example is if an > implementation does not use struct lockf to implement advlock, then > the hack you mention of purging in VOP_RECLAIM is needed. > > After looking over the history of the changes, I believe it would be > sufficient to have the lock purge done before the reclaim. The vnode > is locked exclusively for both operations, so I don't believe there > will be any timing windows. But I am still not 100% sure when the file > lock is used versus the interlock for serializing access to various > fields. > > The advlock VOPs are analogous to the regular VOP_LOCK in that we > expect an implementation may override the VOP and also the data > structures used, e.g. to not use the vnode's v_lock field for the > VOP_LOCK. Thus any code which refers to v_lockf should be wrapped in a > VOP to allow correct overriding.
Essentially, my argument is that whatever you do in VOP_ADVLOCKPURGE, can be and should be done in VOP_RECLAIM. This would also cover the v_data issue.
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