> 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. Thanks, matthew _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
