Re: [RFC PATCH 0/6] Fix NFSv4 delegations

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On Tue, Jan 17, 2012 at 11:00:23AM -0500, J. Bruce Fields wrote:
> From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
> 
> NFSv4 delegations are currently implemented as leases.  However, leases
> don't have quite the same semantics, which means that delegations are
> currently enforced correctly only for conflicts between NFSv4 clients.
> 
> I previously attempted to address this by "fixing" the existing lease
> behavior, assuming it was a bug--but from further investigation it looks
> like that would be the wrong thing to do for Samba.
> 
> So instead I'm defining a new FL_DELEG flag to mark NFSv4 delegations,
> and varying behavior based on that.  Delegations aren't meant to be
> available to userspace for now--nfsd is the only user.
> 
> In theory this code allows both read and write delegations, but I'm only
> using read delegations for now--write delegations are a project for
> another day.  (At which point write leases will probably need some
> fixing while we're at it.)
> 
> Still to do: if OPEN(dirfd, name) returns a delegation to the client,
> then the client should be guaranteed that the opened file is still
> linked as (dirfd, name).  But the current nfsd code allows a rename or
> unlink to intervene between the lookup and the request for a delegation.

OK, I decided I could fix that in the nfsd4 open code by retrying the
lookup after obtaining the delegation, and just dropping the delegation
(they're always optional) if it turned out there'd been a race.

I'll post revised vfs patches (without that extra nfsd stuff).

--b.
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