Re: [nfsv4] seeking clarifications in server-side copy CB_OFFLOAD feature

"J. Bruce Fields" <bfields@fieldses.org> Mon, 06 March 2017 22:07 UTC

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Date: Mon, 06 Mar 2017 17:06:59 -0500
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Olga Kornievskaia <aglo@umich.edu>
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Subject: Re: [nfsv4] seeking clarifications in server-side copy CB_OFFLOAD feature
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On Mon, Mar 06, 2017 at 11:54:44AM -0500, Olga Kornievskaia wrote:
> On Fri, Mar 3, 2017 at 9:07 PM, J. Bruce Fields <bfields@fieldses.org> wrote:
> > On Fri, Mar 03, 2017 at 05:28:17PM -0500, Olga Kornievskaia wrote:
> >> Thanks for the comments Bruce!
> >> > On Thu, Mar 02, 2017 at 04:07:42PM -0500, Olga Kornievskaia wrote:
> >> >> -- related to errors returned in CB_OFFLOAD, there is no guidance with
> >> >> regards to the reboot recovery. If the destination server unable to
> >> >> finish the copy due to the source server rebooting, should it reply
> >> >> back with a successful short copy or should it return some error (and
> >> >> short copy of possibly 0bytes).
> >> >
> >> > A short copy sounds reasonable to me.
> >>
> >> short copy with an error, right?
> >
> > I was thinking without an error, but at least in the case where there
> > were 0 bytes I think you're right there needs to be an error.
> 
> I'm confused :( The way I read things you say server shouldn't hide
> errors but here you are saying it should return a short copy without
> an error. I guess I'll wait for you to comment on the actual code to
> let me know what you think should happen there.

I'd reserve the case of a succesful copy with 0 bytes copied for
end-of-file.  So if we're forced to return without copying anything, and
it's not because of end of file, we should return an error.  If it's a
problem like source-server reboot that would be cured by the client
retrying, the it should be an error that prompts the client to do that.

In the case of a short copy of some number of bytes more than 0, I don't
understand why the protocol allows an error return, but I guess I can't
think of a reason to care whether we return one or not.

--b.