From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55900) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1akyKl-0003R1-9d for qemu-devel@nongnu.org; Tue, 29 Mar 2016 14:25:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1akyKf-0002TI-9A for qemu-devel@nongnu.org; Tue, 29 Mar 2016 14:25:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60937) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1akyKf-0002T0-1B for qemu-devel@nongnu.org; Tue, 29 Mar 2016 14:25:37 -0400 References: <1459173555-4890-1-git-send-email-eblake@redhat.com> <1459223796-28474-2-git-send-email-eblake@redhat.com> <55B49D68-2F63-4742-9B60-F6B428ABB3E9@alex.org.uk> <56FA8F5B.8060800@redhat.com> <88E5F63B-B036-45C7-B2FD-B555D54E88F4@alex.org.uk> <56FA9B42.2020503@redhat.com> <08706CF2-6DA1-421E-827D-6C08CC08A9EA@alex.org.uk> <56FABF49.8080205@redhat.com> <20160329180314.GA12469@grep.be> <56FAC47F.9010807@redhat.com> <20160329181949.GB12469@grep.be> From: Eric Blake Message-ID: <56FAC89F.7080706@redhat.com> Date: Tue, 29 Mar 2016 12:25:35 -0600 MIME-Version: 1.0 In-Reply-To: <20160329181949.GB12469@grep.be> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="9VjpS34aptLSLKIpXo0OBACUDj4kKH34s" Subject: Re: [Qemu-devel] [Nbd] [PATCH 3/1] doc: Propose Structured Replies extension List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wouter Verhelst Cc: "nbd-general@lists.sourceforge.net" , "qemu-devel@nongnu.org" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --9VjpS34aptLSLKIpXo0OBACUDj4kKH34s Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 03/29/2016 12:19 PM, Wouter Verhelst wrote: > On Tue, Mar 29, 2016 at 12:07:59PM -0600, Eric Blake wrote: >> On 03/29/2016 12:03 PM, Wouter Verhelst wrote: >>> On Tue, Mar 29, 2016 at 11:45:45AM -0600, Eric Blake wrote: >>>> Supporting DF merely transfers the burden of collection between serv= er >>>> and client. I suspect that there are cases where the server does NO= T >>>> want to support DF (because it would require the server to allocate >>>> memory to collect the data before sending a single structured read >>>> reply), >>> >>> There are other ways to handle that; e.g., the server could have a >>> "request too large for non-fragmented read" error message. The spec >>> should give a minimum size that the server MUST support (which should= be >>> reasonably large), and should state that a server MAY reply to any >>> request with DF set for a block larger than that minimum, with that >>> error. >> >> How does 64k sound? >=20 > Dunno. It might make sense for this number to be based upon some > "standard" minimum request size in things like ATA or SCSI if such a > number exists there, but I don't know enough about either standard to > answer that question myself. >=20 > If such a number doesn't exist (or nobody who knows speaks up soon > enough), 64k is certainly good enough, I suppose. And as mentioned in another email, we may want to propose an independent extension that allows NBD_OPT_LIST and friends to start advertising the minimum and preferred sizes of operations on a given export, where the server can give hard errors if the client requests a read or write not aligned to the minimum, and where the server must not fail a DF set for anything smaller than preferred size. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --9VjpS34aptLSLKIpXo0OBACUDj4kKH34s 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/ iQEcBAEBCAAGBQJW+sifAAoJEKeha0olJ0Nq/OAH/Rx2x1DN6OqgkU8iJkGg1M4m 5U/UAy6kDwVef1PZnn5CYf1M19MZcKaMzy4W7WKB6bMsC3gKStdppTOG/xNPVMa1 3LW6wSa5M3jwJi5RaTyDBjI44eQLNCaUkkPyGhuQmk4AcI10kg00jNr+R6BhRZHm gp/ivkriiWp6bQceWxB/B0VgAThPmOZ+j9h0AqxiCK4D4gl0iDjGJccuifOuARkb 7oUi/0Ol2SkEj/IyxNgELtZRvbc71e0Jaq0yTrQDGPUAK7hsDSYFa9yTBbe/myqI xwmaE5PLA2m7va0kR/xKy6K5oin5cMo3ZuoRCOiAPaYXQXVFS+yJfr2sH+G/jmU= =wgEg -----END PGP SIGNATURE----- --9VjpS34aptLSLKIpXo0OBACUDj4kKH34s--