Date: Mon, 17 May 2010 08:33:52 -0700 From: "Matthew Fleming" <matthew.fleming@isilon.com> To: "Kostik Belousov" <kostikbel@gmail.com>, "Zachary Loafman" <zml@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: RE: svn commit: r208003 - in head/sys: kern sys Message-ID: <06D5F9F6F655AD4C92E28B662F7F853E021D4D66@seaxch09.desktop.isilon.com> References: <201005122124.o4CLOk3b027904@svn.freebsd.org> <20100516050651.GZ83316@deviant.kiev.zoral.com.ua>
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> From: Kostik Belousov [mailto:kostikbel@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 > >=20 > > 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_*) > > =20 > > Submitted by: Matthew Fleming <matthew.fleming@isilon.com> > > Reviewed by: zml, dfr >=20 > 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. >=20 > 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
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