linux-kernel - Re: Grace period

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Message-ID: <20120409161114.GB6482@fieldses.org>
Date:	Mon, 9 Apr 2012 12:11:14 -0400
From:	"bfields@...ldses.org" <bfields@...ldses.org>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	Jeff Layton <jlayton@...hat.com>,
	"Trond.Myklebust@...app.com" <Trond.Myklebust@...app.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Grace period

On Mon, Apr 09, 2012 at 08:08:57PM +0400, Stanislav Kinsbursky wrote:
> 09.04.2012 19:27, Jeff Layton пишет:
> >
> >If you allow one container to hand out conflicting locks while another
> >container is allowing reclaims, then you can end up with some very
> >difficult to debug silent data corruption. That's the worst possible
> >outcome, IMO. We really need to actively keep people from shooting
> >themselves in the foot here.
> >
> >One possibility might be to only allow filesystems to be exported from
> >a single container at a time (and allow that to be overridable somehow
> >once we have a working active/active serving solution). With that, you
> >may be able limp along with a per-container grace period handling
> >scheme like you're proposing.
> >
> 
> Ok then. Keeping people from shooting themselves here sounds reasonable.
> And I like the idea of exporting a filesystem only from once per
> network namespace.

Unfortunately that's not going to get us very far, especially not in the
v4 case where we've got the common read-only pseudoroot that everyone
has to share.

--b.

> Looks like there should be a list of pairs
> "exported superblock - network namespace". And if superblock is
> exported already in other namespace, then export in new namespace
> have to be skipped (replaced?) with appropriate warning (error?)
> message shown in log.
> Or maybe we even should deny starting of NFS server if one of it's
> exports is shared already by other NFS server "instance"?
> But any of these ideas would be easy to implement in RAM, and thus
> it suits only for containers...
> 
> -- 
> Best regards,
> Stanislav Kinsbursky
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