On Jul 23, 2009, at 11:10 AM, Rick Macklem wrote:
I really don't want to enable write delegations until we figure
out how
to enforce them correctly against local (non-nfs) users of the
exported
filesystem as well. In addition to breaking delegations on read
opens,
that means breaking delegations or doing a cb_getattr on
operations like
stat.
do you know whether there are local FS where the maintainers at
least plan
to incorporate delegations?
I'm not a Linux guy, so I'm not familiar with the internal
structure, but...
in general, I don't think the problem is with local file systems.
Usually
the problem is with local system call access. For example, if a
process running locally on the server opens a file, the delegation
should
be recalled, so that changes done locally on the client get flushed
back
to the server. Also, a write delegation allows a client to do byte
range
locking locally in the client, so the write delegation needs to be
recalled before anything gets a byte range lock locally in the server.
The delegation implementation on the Linux server uses the vfs lease
subsystem, and so is integrated with local access - conflicting opens
done locally do recall delegations. But the last time I looked, the
lease subsystem is not complete as it doesn't recall leases (nor
delegations) on remove, rename, etc. Another problem is that while
write delegations improve performance for certain workloads, they kill
performance for others.
-->Andy
A Samba server running in the nfs server would be doing "local" ops
for the purpose of this discussion. (I'm not sure if Samba goes as far
as doing Open/Share locks for clients?)
rick
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