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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id B8DD3C3ABA3 for ; Thu, 1 May 2025 17:25:06 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uAXea-0006hR-Nr; Thu, 01 May 2025 13:24:56 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uAXeX-0006f7-4K for qemu-devel@nongnu.org; Thu, 01 May 2025 13:24:53 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uAXeS-0003mK-TW for qemu-devel@nongnu.org; Thu, 01 May 2025 13:24:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1746120286; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=gwObnzzThY3+zonLKz3VC2JUpgLaHKlX4Qb+c5J1LHQ=; b=A4Vx69NBQ9kW9SJvs3BWTtPRZfKS4sZP3juYqPNKjM0x2oZiil/LWUJYeRLVBJQOaPy24A 4dsZqYN11oOZWiiAI07RDXpFQNccFT9EUCI5pXOTUaL3GrHahws1rxzlNTbl4uD08m9Rfp FYqMtrYi7LeCjvfY4pb8rR1DUaXl0jg= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-693-MpQVhCwnNeGB6SYQsWCGLw-1; Thu, 01 May 2025 13:24:41 -0400 X-MC-Unique: MpQVhCwnNeGB6SYQsWCGLw-1 X-Mimecast-MFC-AGG-ID: MpQVhCwnNeGB6SYQsWCGLw_1746120280 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 151CE180087B; Thu, 1 May 2025 17:24:40 +0000 (UTC) Received: from localhost (unknown [10.2.16.99]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id CAF4C19560AD; Thu, 1 May 2025 17:24:38 +0000 (UTC) Date: Thu, 1 May 2025 13:24:37 -0400 From: Stefan Hajnoczi To: Eric Blake Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, vsementsov@yandex-team.ru, Fam Zheng , Kevin Wolf , Hanna Reitz Subject: Re: [PATCH v3 04/11] block: Add new bdrv_co_is_all_zeroes() function Message-ID: <20250501172437.GE99177@fedora> References: <20250425005439.2252467-13-eblake@redhat.com> <20250425005439.2252467-17-eblake@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="ZmkU+vxBg3EgNRLk" Content-Disposition: inline In-Reply-To: <20250425005439.2252467-17-eblake@redhat.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.644, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --ZmkU+vxBg3EgNRLk Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Apr 24, 2025 at 07:52:04PM -0500, Eric Blake wrote: > There are some optimizations that require knowing if an image starts > out as reading all zeroes, such as making blockdev-mirror faster by > skipping the copying of source zeroes to the destination. The > existing bdrv_co_is_zero_fast() is a good building block for answering > this question, but it tends to give an answer of 0 for a file we just > created via QMP 'blockdev-create' or similar (such as 'qemu-img create > -f raw'). Why? Because file-posix.c insists on allocating a tiny > header to any file rather than leaving it 100% sparse, due to some > filesystems that are unable to answer alignment probes on a hole. But > teaching file-posix.c to read the tiny header doesn't scale - the > problem of a small header is also visible when libvirt sets up an NBD > client to a just-created file on a migration destination host. >=20 > So, we need a wrapper function that handles a bit more complexity in a > common manner for all block devices - when the BDS is mostly a hole, > but has a small non-hole header, it is still worth the time to read > that header and check if it reads as all zeroes before giving up and > returning a pessimistic answer. >=20 > Signed-off-by: Eric Blake >=20 > --- >=20 > v3: Use constant 128k as maximum data header size to read [Stefan] > --- > include/block/block-io.h | 2 ++ > block/io.c | 62 ++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 64 insertions(+) Reviewed-by: Stefan Hajnoczi --ZmkU+vxBg3EgNRLk Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQEzBAEBCgAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmgTrlUACgkQnKSrs4Gr c8iwCggAyc9lVIprzjC1zC/+Q8xzLgxrESnwtrKJmzY2Ru+GyDEVd5bWwDVdV/6/ FKgaeSCo6KUz3ZkoNI6ZqPJhFbYFiLXbwqEUl9/G943hBNK50dspHK0zx3BAbClM QDJaC+CxvXP4QULhuB9Fkh76BiCpTaKrLBDyR3p+osREwX9Chbm4Yxs0tfXqmid3 bgelFE+hnlVby8ePmV5Xcm5+yamzrAZUvwul8tdyxC3au3Z7Sx92gKiwDLCOuW9X J4vEQ/nRfWCdL5iwiDdc6XO9lZit0w23odOA75o+gteUTe5oW0/+rFuhK6M8GzoW iCHRHIvOCDNF443Lw1NF7UcZ6Ue63w== =wlfo -----END PGP SIGNATURE----- --ZmkU+vxBg3EgNRLk--