From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:42903) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TqSdS-00049t-3s for qemu-devel@nongnu.org; Wed, 02 Jan 2013 13:01:54 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TqSdI-0007re-MB for qemu-devel@nongnu.org; Wed, 02 Jan 2013 13:01:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:62537) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TqSdI-0007rX-DZ for qemu-devel@nongnu.org; Wed, 02 Jan 2013 13:01:40 -0500 Message-ID: <50E475E0.2080103@redhat.com> Date: Wed, 02 Jan 2013 11:01:04 -0700 From: Eric Blake MIME-Version: 1.0 References: <1357143393-29832-1-git-send-email-benoit@irqsave.net> <20130102171057.GP19472@us.grid.coop> <20130102173324.GB29742@irqsave.net> In-Reply-To: <20130102173324.GB29742@irqsave.net> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="------------enigF29216DBAA8BF372CE80E7AB" Subject: Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?UTF-8?B?QmVub8OudCBDYW5ldA==?= Cc: kwolf@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, pbonzini@redhat.com This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigF29216DBAA8BF372CE80E7AB Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 01/02/2013 10:33 AM, Beno=C3=AEt Canet wrote: >> How does this code handle hash collisions, and do you have some regres= sion >> tests that purposefully create a dedup hash collision, and verify that= the >> 'right thing' happens? >=20 > The two hash function that can be used are cryptographics and not broke= n yet. > So nobody knows how to generate a collision. I can understand that it is hard to write a test for two distinct data sectors hashing to the same value, but perhaps it's worth including a debug-only hash algorithm that intentionally generates collisions, just to prove that you handle them correctly. De-duplicating collided data, while unlikely, is still a case of data loss that not everyone is happy to risk. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --------------enigF29216DBAA8BF372CE80E7AB Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with undefined - http://www.enigmail.net/ iQEcBAEBCAAGBQJQ5HXgAAoJEKeha0olJ0NqokQH/0JQ3A0yTwbHg4VxHv7MYFrx tVwlCY8xDZeCcUWVK6hQSf4qarXOKcNZ5nfSvd6Et1A1XuNCrkOlKh3eZQ+UfKmz KFq95hn5uuu34j4088kegl2l4EQfCLWhM8RSZhHoJl6KIm+43Fac1OuW1R/pNbeW 0v4fdcE1wgg7jvue31MESkfQ6T9O71+Wyr1qmjGuaoGndhNAgSOT9NxLqhXYM3TQ 02CxEN9lmLTHAscvT0XtKmzAt0jg2oGhhw8skR48IxGqw5Pa87wMdGP7q2eiXx3W RRNctguMLKjtcAcpeoRSQve7xQYImGBe0mdps4XHOmMJU3MrYNBBpVnBUvYIskI= =jNy3 -----END PGP SIGNATURE----- --------------enigF29216DBAA8BF372CE80E7AB--