Date: Fri, 23 Dec 2011 09:23:16 -0500 From: John Baldwin <jhb@freebsd.org> To: "Robert N. M. Watson" <rwatson@freebsd.org> Cc: arch@freebsd.org Subject: Re: Post NOTE_ATTRIB EVFILT_VNODE events for extattr changes Message-ID: <201112230923.16333.jhb@freebsd.org> In-Reply-To: <E6AD9F35-90F2-466F-89A2-587E0C1309FF@freebsd.org> References: <201112221105.31746.jhb@freebsd.org> <E6AD9F35-90F2-466F-89A2-587E0C1309FF@freebsd.org>
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On Thursday, December 22, 2011 6:19:27 pm Robert N. M. Watson wrote:
>
> On 22 Dec 2011, at 16:05, John Baldwin wrote:
>
> > A co-worker noticed that there is currently no way to get an EVFILT_VNODE
> > notification if the extended attributes for a given file change. I looked at
> > OS X and found that it posts a NOTE_ATTRIB event (typically used for
> > VOP_SETATTR()) for successful attempts to set or delete an extended attribute.
> > I have a patch to do the same along with a test application for both OS X and
> > FreeBSD. With this patch FreeBSD now has the same behavior as OS X.
>
> This seems reasonable to me, although I've not tested the patch you attached myself.
>
> I'm not familiar with the pre/post-vop hook mechanism, but I assume that this will fire when internal extended attribute I/O, for example
triggered by ACL changes, occurs?
The hooks fire anytime VOP_SETEXTATTR() or VOP_DELETEEXTATTR() are called. What
happens is that calls to the hooks are inserted into the macro functions generated
in vnode_if.c, for example:
int
VOP_SETEXTATTR_APV(struct vop_vector *vop, struct vop_setextattr_args *a)
{
int rc;
VNASSERT(a->a_gen.a_desc == &vop_setextattr_desc, a->a_vp,
("Wrong a_desc in vop_setextattr(%p, %p)", a->a_vp, a));
while(vop != NULL && \
vop->vop_setextattr == NULL && vop->vop_bypass == NULL)
vop = vop->vop_default;
VNASSERT(vop != NULL, a->a_vp, ("No vop_setextattr(%p, %p)", a->a_vp, a));
SDT_PROBE(vfs, vop, vop_setextattr, entry, a->a_vp, a, 0, 0, 0);
ASSERT_VI_UNLOCKED(a->a_vp, "VOP_SETEXTATTR");
ASSERT_VOP_ELOCKED(a->a_vp, "VOP_SETEXTATTR");
if (vop->vop_setextattr != NULL)
rc = vop->vop_setextattr(a);
else
rc = vop->vop_bypass(&a->a_gen);
CTR6(KTR_VOP,
"VOP_SETEXTATTR(vp 0x%lX, attrnamespace %ld, name 0x%lX, uio 0x%lX, cred 0x%lX, td 0x%lX)",
a->a_vp, a->a_attrnamespace, a->a_name, a->a_uio, a->a_cred, a->a_td);
SDT_PROBE(vfs, vop, vop_setextattr, return, a->a_vp, a, rc, 0, 0);
if (rc == 0) {
ASSERT_VI_UNLOCKED(a->a_vp, "VOP_SETEXTATTR");
ASSERT_VOP_ELOCKED(a->a_vp, "VOP_SETEXTATTR");
} else {
ASSERT_VI_UNLOCKED(a->a_vp, "VOP_SETEXTATTR");
ASSERT_VOP_ELOCKED(a->a_vp, "VOP_SETEXTATTR");
}
vop_setextattr_post(a, rc);
return (rc);
}
Thus, if the ACL code uses VOP_SETEXTATTR() and VOP_DELETEEXTATTR() then it
will trigger this, yes. Checking UFS, it's ACL VOPs use vn_extattr_rm() and
vn_extattr_set() which are wrappers around the the EA VOP's, so toggling
ACL's will trigger NOTE_ATTRIB on UFS. I'm not sure if it is worth it to
fire an explicit event for VOP_SETACL() as well. OS X does not appear to
have a VOP_SETACL() that I can see (they just assume ACL's are always stored
as EA's at the vnode layer), so I can't use that as a model.
--
John Baldwin
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