ZFS, procfs and java

Pawel Jakub Dawidek pjd at FreeBSD.org
Sat Apr 21 10:12:26 UTC 2007

On Sat, Apr 21, 2007 at 11:08:21AM +0100, Robert Watson wrote:
> On Fri, 20 Apr 2007, Stephane E. Potvin wrote:
> >It seems that the ZFS cache (dnlc) doesn't update the VSF_namecache fields in the vnodes (v_cache_src, v_cache_dst and v_dd). This unfortunately causes the file link in 
> >/proc/curproc to return "unknown" as it uses vn_fullpath which relies on the namecache fields to be set correctly.
> >
> >Java uses /proc/curproc/file to know where to find its libraries and doesn't expect the "unknown" return value returned when using ZFS (due to vn_fullpath failing). The 
> >attached patches to the java/jdk15 port fixes this issue but it doesn't fix the root of the problem.
> >
> >Would it be possible to add support in dnlc for updating the VFS namecache fields or to add knowledge of dnlc into vn_fullpath?
> No application should rely on the correctness and usefulness of /proc/curproc/file -- the conversion from a vnode to a pathname is inherently unreliable.  Likewise, 
> properly ported applications should not rely on the availability of procfs, as its use is deprecated.  My advice would be to talk to the Java porters about entirely 
> eliminating this dependency.
> As a matter of debugging/logging convenience, it would be nice if ZFS implemented the name cache hooks, since using vn_fullpath is useful for procfs monitoring of process 
> address space, audit, etc.

I tried to teach ZFS about our namecache (the code is under
FREEBSD_NAMECACHE define), but it didn't worked stable, I'm probably
still missing something. On the other hand it was rather easy to use
namecache from OpenSolaris with ZFS (DNLC).

Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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