From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9B931C3A589 for ; Fri, 16 Aug 2019 02:10:17 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 677262086C for ; Fri, 16 Aug 2019 02:10:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 677262086C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48468 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1hyRh2-00063a-Hm for qemu-devel@archiver.kernel.org; Thu, 15 Aug 2019 22:10:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59382) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1hyRgB-0005ZV-HL for qemu-devel@nongnu.org; Thu, 15 Aug 2019 22:09:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hyRgA-0003vv-A7 for qemu-devel@nongnu.org; Thu, 15 Aug 2019 22:09:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45856) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hyRg7-0003uW-Dm; Thu, 15 Aug 2019 22:09:19 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A43FF30821A1; Fri, 16 Aug 2019 02:09:18 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-204-21.brq.redhat.com [10.40.204.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F07FF17156; Fri, 16 Aug 2019 02:09:16 +0000 (UTC) From: Max Reitz To: Eric Blake , qemu-block@nongnu.org References: <20190730172508.19911-1-mreitz@redhat.com> <20190730172508.19911-3-mreitz@redhat.com> <9f7db4bc-d66a-2069-9f9a-20da842829f3@redhat.com> <60b73760-9ffd-aedf-afc0-9c58c804236c@redhat.com> Openpgp: preference=signencrypt Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <10daecff-15b4-88f0-9fe8-f5c5547fde70@redhat.com> Date: Fri, 16 Aug 2019 04:09:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <60b73760-9ffd-aedf-afc0-9c58c804236c@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="oOfEOPGoqtLVaIFcxkHnCe54g1Mkxs8yB" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Fri, 16 Aug 2019 02:09:18 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH for-4.2 02/13] qcow2: Keep unknown extra snapshot data X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --oOfEOPGoqtLVaIFcxkHnCe54g1Mkxs8yB Content-Type: multipart/mixed; boundary="crjVhCdzBBWLu1FXZGCBCfN57WAUXsWtu"; protected-headers="v1" From: Max Reitz To: Eric Blake , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Kevin Wolf Message-ID: <10daecff-15b4-88f0-9fe8-f5c5547fde70@redhat.com> Subject: Re: [PATCH for-4.2 02/13] qcow2: Keep unknown extra snapshot data References: <20190730172508.19911-1-mreitz@redhat.com> <20190730172508.19911-3-mreitz@redhat.com> <9f7db4bc-d66a-2069-9f9a-20da842829f3@redhat.com> <60b73760-9ffd-aedf-afc0-9c58c804236c@redhat.com> In-Reply-To: <60b73760-9ffd-aedf-afc0-9c58c804236c@redhat.com> --crjVhCdzBBWLu1FXZGCBCfN57WAUXsWtu Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 31.07.19 10:54, Max Reitz wrote: > On 30.07.19 19:56, Eric Blake wrote: >> On 7/30/19 12:24 PM, Max Reitz wrote: [...] >>> + if (sn->extra_data_size > sizeof(extra)) { >>> + /* Store unknown extra data */ >>> + size_t unknown_extra_data_size =3D >>> + sn->extra_data_size - sizeof(extra); >>> + >>> + sn->unknown_extra_data =3D g_malloc(unknown_extra_data_s= ize); >>> + ret =3D bdrv_pread(bs->file, offset, sn->unknown_extra_d= ata, >>> + unknown_extra_data_size); >> >> We're doing two separate bdrv_pread()s. Would it be better to do a >> single bdrv_preadv into a vector composed of &extra and >> &unknown_extra_data, for less I/O? (Then again, this micro-optimizati= on >> is probably in the noise in the long run) >=20 > Interesting idea, we could even add the ID and name string into that > vector. But I=E2=80=99m not sure whether it=E2=80=99s really useful. >=20 > (I=E2=80=99ll take a look anyway, because it sounds interesting.) I did, and it was actually really nice. I liked it. (I don=E2=80=99t hi= nk the performance is important, but it was actually just simpler.) But then it turned out that it won=E2=80=99t work with patch 8, because a= fter that we may want to skip parts of the unknown extra data =E2=80=93 and sk= ipping doesn=E2=80=99t work with bdrv_preadv()... (So all the simplicity is lost, and that=E2=80=99s what I was interested = in.) But it was indeed quite cool. :-/ Max --crjVhCdzBBWLu1FXZGCBCfN57WAUXsWtu-- --oOfEOPGoqtLVaIFcxkHnCe54g1Mkxs8yB Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl1WEEoACgkQ9AfbAGHV z0AF7gf/ZGh5qy5yB7cNFE2I16nJR6Uc7C4aU6kl4mO9UiHnyUnLa4rMPuXDki58 oq29udvNAbwbO94GVru2Bgf5lZaDSlmwaxhgEs62N0El+gBecVEBT9XpBZihSC4T piXa85Y6EsUudW1YUuWKoM0Oc83P5h5F/doVL9DlDcxWNhSmmC1pjJ5tbYcPpRqg /Zl/8LnrcD6YgpPMFafPBzsR7g1RDOHegmazkNmTGKBQ4UQs1p3ksWH6Dunbg+ye UcMw1I9oNBPf69SuCG7HcyY9WjSb/YfJ8LjcBTpNSCY6Qo7tU/qq5n5etHisBQYO pxr19C4JobuEub4W1+dtB1iUrRuQuw== =5fUC -----END PGP SIGNATURE----- --oOfEOPGoqtLVaIFcxkHnCe54g1Mkxs8yB--