From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44767) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b2iIk-0004Q1-03 for qemu-devel@nongnu.org; Tue, 17 May 2016 12:56:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b2iIe-0008QY-W5 for qemu-devel@nongnu.org; Tue, 17 May 2016 12:56:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46699) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b2iIe-0008QS-Nm for qemu-devel@nongnu.org; Tue, 17 May 2016 12:56:52 -0400 References: <1455640486-6101-1-git-send-email-pbonzini@redhat.com> <1455640486-6101-24-git-send-email-pbonzini@redhat.com> <20160517095339.GD28935@redhat.com> <573B342E.8030208@redhat.com> <5ED6FB6F-5023-4833-83F9-B24BD379E2CD@alex.org.uk> <573B3E3E.60902@redhat.com> <20160517155820.GZ1683@redhat.com> <573B415E.6080208@redhat.com> <20160517164112.GB1683@redhat.com> From: Eric Blake Message-ID: <573B4D53.80703@redhat.com> Date: Tue, 17 May 2016 10:56:51 -0600 MIME-Version: 1.0 In-Reply-To: <20160517164112.GB1683@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="JoNRbEUsuSsJ0HM3F4eFwUK8AJPtElMmn" Subject: Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Richard W.M. Jones" Cc: Alex Bligh , Paolo Bonzini , "Daniel P. Berrange" , "nbd-general@lists.sourceforge.net" , "qemu-devel@nongnu.org" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --JoNRbEUsuSsJ0HM3F4eFwUK8AJPtElMmn Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 05/17/2016 10:41 AM, Richard W.M. Jones wrote: > On Tue, May 17, 2016 at 10:05:50AM -0600, Eric Blake wrote: >> On 05/17/2016 09:58 AM, Richard W.M. Jones wrote: >>> On Tue, May 17, 2016 at 09:52:30AM -0600, Eric Blake wrote: >>>> so it might be nicer to >>>> make a change to the protocol document that instead permits current >>>> nbdkit behavior and puts the burden on clients to interoperate when >>>> NBD_OPT_LIST is not supported. >>> >>> The purpose of nbdkit is to be a server for qemu, to be a replacement= >>> for qemu-nbd in cases where proprietary code cannot be combined with >>> qemu for copyright/licensing/legal reasons. So we aim to make sure w= e >>> can interoperate with qemu. No need to change any standards for >>> nbdkit! Clarifying standards documents is OK though. >> >> I also noticed that nbdkit forcefully rejects a client that sends more= >> than 32 NBD_OPT_ commands, even though this is perfectly valid behavio= r >> on the part of the client. Maybe the protocol should document a >> (higher) limit on minimum number of options a client can expect to be >> serviced before the server dropping the connection because the client = is >> wasting the server's time. >=20 > This, as you say, is a brake on clients that try to waste time by > sending infinite numbers of options. Is there any danger that 32 is > too small? Yes. Consider a client that connects to a server that lists more than 32 exports in NBD_OPT_LIST, then the client calls (the still-experimental) NBD_OPT_INFO on each of those exports, to learn further details about each export, before finally using NBD_OPT_GO to pick the one the user likes best. That's why I wonder if we need to document a minimum cutoff at which clients should assume will always be serviced, and which servers should not treat as an attack, and whether it should be larger than 32. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --JoNRbEUsuSsJ0HM3F4eFwUK8AJPtElMmn Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJXO01TAAoJEKeha0olJ0NqCsQH+wR7oJ7LjMbKfaAwNHcbVtN6 RXEoSe4M5xcz6d2Lgp+2JRvAQ1cJrz11C/CiZhLfMq651oICEoG3q9m/JfiJjMMP fLVCQtGj+f0IvPQEgnGOm/FKMLpsdMQhAE+63EaxO28uzx1aS2T9AwC8XZRuEwC9 UuYAMFUF0+AbVv4p2QmN69Zo0l7gY0eF4BT/hqVqh7I1jKdu+v4uyzmhfbnQll9H rmJdqK2flhndGax6vyBiwZppc/AAudgFv4K0Vrb7UDr7VQOjqqdBW4srucNQToAF XXU8udeecjTzJbr/bEtypkpe4K276WeMqz1ZmX8DbybvRlU4mDbLxflhrslDTU0= =TE8f -----END PGP SIGNATURE----- --JoNRbEUsuSsJ0HM3F4eFwUK8AJPtElMmn--