linux-kernel - Re: [NFS] [PATCH 008 of 11] knfsd: Prepare knfsd for support of rsize/wsize of up to 1MB, over TCP.

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Message-ID: <20061003021304.GB12867@fieldses.org>
Date:	Mon, 2 Oct 2006 22:13:04 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Neil Brown <neilb@...e.de>
Cc:	nfs@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	Greg Banks <gnb@...bourne.sgi.com>
Subject: Re: [NFS] [PATCH 008 of 11] knfsd: Prepare knfsd for support of	rsize/wsize of up to 1MB, over TCP.

On Tue, Oct 03, 2006 at 11:36:32AM +1000, Neil Brown wrote:
> The only real problem is that NFSv4 can have arbitrarily large
> non-payload data, and arbitrarily many payloads.  But I guess any
> client that trying to send two full-sized payloads in the one request
> is asking for trouble (I don't suppose the RPC spells this out at
> all?).

The RFC?  Well, it does have a "RESOURCE" error that the server can
return for overly complicated compounds.  It doesn't give much guidance
on when exactly that could happen, but if there's ever a clear case for
returning NFS4ERR_RESOURCE, I think it must be the case of a client
trying to circumvent the maximum read/write size by using multiple read
or write operations in a single compound.

(We have some other odd restrictions on the sorts of compounds we can
accept, which I'd like to relax.  But that's a problem for another day.)

> And the fact that the code change to effect this is so tiny seems to
> imply that most of the code was already assuming that sv_bufsz was
> really the payload size rather than the packet size.

There's also the check at the end of svc_tcp_recvfrom():

	if (svsk->sk_reclen > serv->sv_bufsz) {
		printk(KERN_NOTICE "RPC: bad TCP reclen 0x%08lx (large)\n",
		       (unsigned long) svsk->sk_reclen);
		goto err_delete;
	}

--b.
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