[RFC][PATCH 0/5] NFS: trace points added to mounting path

Steve Dickson
2009-01-16T16:25:26Z

Hello,

Very recently patches were added to the mainline kernel that
enabled the use of trace points. This patch series takes
advantage of those patch by introducing trace points
to the mounting path of NFS mounts. Its hoped these
trace points can be used by system administrators to
identify why NFS mounts are failing or hang in
production kernels.

IMHO, one general problem with today's "canned" NFS debugging today is it
becomes very verbose very quickly.... "I get here" and "I get there" type of
debugging statements. Although they help trace the code but very rarely
shows/defines what the actual problem was. So what I've try to do is
"define the error paths" by putting a trace point at every error exit
in hopes to define where and why things broke.

So the ultimate goal would be to replace all the dprintks with trace points
but still be able to enable them through the rpcdebug command (although we
might want to think about splitting the command out into three different
commands nfsdebug, nfsddebug, rpcdebug). Since trace points have very little
overhead, a set of trace points could be enable in production with have
little or no effect on functionality or performance.

Another advantage with trace points is the type and amount of
information that can be retrieved. With these trace points, I'm
passing in the error code as well as the data structure[s] associated
with that error. This allows the "canned" information that IT people
would used (via the rpcdebug command which would turn on a group of
trace points) as well as more detailed information that kernel developers
can used (via systemtap scripts which would turn on individual trace
points).

Patch summary:
* fs/nfs/client.c

* fs/nfs/getroot.c

* fs/nfs/super.c

The based files where traces where added.

* include/trace/nfs.h

* kernel/trace/Makefile

* kernel/trace/nfs-trace.c

The overhead of added the trace points and then converting them
into trace marks .

* samples/nfs/nfs_mount.stp

The systemtap script used to access the trace marks. I probably
should have documented the file better, but the first three
functions in the file are how structures are pulled from the
kernel. The rest are probes used to active the trace markers.

Comments... Acceptance??

steved.