RFC: New VOP to translate vnode to its component name

[Joe Marcus Clarke]

On Mon, 2008-12-08 at 18:08 +0000, Robert Watson wrote:
> On Sun, 7 Dec 2008, Peter Wemm wrote:
> 
> > Well, you already know I love the idea.  Valgrind "knows" that you can 
> > obtain the pathname from a fd or mmap address reliably at any time because 
> > of procfs on linux, so its code is structured with that assumption.
> 
> Just to give a general vote of "we need to do something here, whether the 
> details are exactly these or not" -- having better object->path resolution is 
> quite important for audit, as well as if we want to adopt a file system 
> notification services along the lines of Apple's fsevents (which is 
> path-centric and operates from close() events rather than open() events).  I 
> don't think we should run in the Linux 'dentry' direction, but having a more 
> robust translation service would be quite valuable.  One comment: I think we 
> should continue to have a KPI which does a sleep-free translation to call, but 
> with weaker semantics than one that is sleepable and can query for more robust 
> reverse lookup.

Okay, what about a name?

vn_fullpath_cache
vn_fullpath_quick
vn_fullpath_fast
vn_fullpath_nosleep
...

Joe

> 
> Robert N M Watson
> Computer Laboratory
> University of Cambridge
> 
> >
> > Using procfs (on 4.x and 6.x) or the kinfo stuff on 7.x+ sort of
> > works, but it quickly becomes unusable if any paths involve NFS.  nfs
> > times out its cached items very quickly.
> >
> > Anyway, I see this as a good first step.  I very much want to see a
> > real vop_default implementation that does the readdir("..") method to
> > fill in the gaps. It isn't particularly important to me if
> > vn_fullpath() recovers the original pathname or not, so long as it can
> > find *a* valid pathname that will work.
> >
> > As for names.. VOP_CNP doesn't tell me what it does at a glance.  Ideas:
> > VOP_VPTOCNP  (vnode to component name, or VOP_VNTOCNP)
> > VOP_RLOOKUP (reverse lookup)
> >
> > We have precedent for the first form.  VOP_FHTOVP().
> >
> > I don't think VOP_VPTOCNP() is too unwieldy and I think it would be a
> > little more intuitive to a casual observer.  I don't want to get
> > trapped in a bikeshed sized To:/CC: list over it though.  I'd rather
> > see it committed to head and get some progress.
> >
> > BTW: at work we do extensive open-by-filehandle stuff on NFS.  For the
> > vast majority of vnodes on those machines, there never was a name
> > cache entry.  It would be priceless if the vop_default readdir(..)
> > method could discover those names in procstat etc.
> >
> > -- 
> > Peter Wemm - peter at wemm.org; peter at FreeBSD.org; peter at yahoo-inc.com; KI6FJV
> > "All of this is for nothing if we don't go to the stars" - JMS/B5
> > "If Java had true garbage collection, most programs would delete
> > themselves upon execution." -- Robert Sewell
> > _______________________________________________
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> >
> 
-- 
Joe Marcus Clarke
FreeBSD GNOME Team      ::      gnome at FreeBSD.org
FreeNode / #freebsd-gnome
http://www.FreeBSD.org/gnome
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