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 46783C54E58 for ; Tue, 12 Mar 2024 21:34:56 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rk9le-0000tq-6B; Tue, 12 Mar 2024 17:34:38 -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 1rk9lb-0000tL-4x for qemu-devel@nongnu.org; Tue, 12 Mar 2024 17:34:35 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rk9lZ-0002T3-D7 for qemu-devel@nongnu.org; Tue, 12 Mar 2024 17:34:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1710279272; 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=Yhi4mPxe+MZ2b3KijonWxPn64duCQdPF/Um8HURpQRE=; b=SM0ruBv8h8Sh6ouORFxSeSooelV9x56g7ouR1PraYiP5j+DWpbnWFcO+6JPVZI+9UauG9F h09nmE7FkF+92pOPF0nxAvQS8UkdnWPVbKcIaA60jSpM8kUWuQih75K+hg+xmJe7DpwbVu igjO9hwLKMIhxxJMYk3n64PCa6oU+ac= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-686-6GiNgxJrM1-h2t_zXTZS1g-1; Tue, 12 Mar 2024 17:34:29 -0400 X-MC-Unique: 6GiNgxJrM1-h2t_zXTZS1g-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3F68228EC113; Tue, 12 Mar 2024 21:34:29 +0000 (UTC) Received: from localhost (unknown [10.39.192.51]) by smtp.corp.redhat.com (Postfix) with ESMTP id 85C3E40C6CB2; Tue, 12 Mar 2024 21:34:28 +0000 (UTC) Date: Tue, 12 Mar 2024 17:34:26 -0400 From: Stefan Hajnoczi To: =?iso-8859-1?Q?C=E9dric?= Le Goater Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Peter Xu , Fabiano Rosas , Markus Armbruster , Kevin Wolf Subject: Re: [PATCH for 9.0] migration: Skip only empty block devices Message-ID: <20240312213426.GA449817@fedora> References: <20240312120431.550054-1-clg@redhat.com> <20240312184106.GC389553@fedora> <1b9016a1-ad58-47ba-9dda-96095c1e59bc@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="cc+9LwI24sP4RmF7" Content-Disposition: inline In-Reply-To: <1b9016a1-ad58-47ba-9dda-96095c1e59bc@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.687, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham 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 --cc+9LwI24sP4RmF7 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Mar 12, 2024 at 09:22:06PM +0100, C=E9dric Le Goater wrote: > On 3/12/24 19:41, Stefan Hajnoczi wrote: > > On Tue, Mar 12, 2024 at 01:04:31PM +0100, C=E9dric Le Goater wrote: > > > The block .save_setup() handler calls a helper routine > > > init_blk_migration() which builds a list of block devices to take into > > > account for migration. When one device is found to be empty (sectors > > > =3D=3D 0), the loop exits and all the remaining devices are ignored. = This > > > is a regression introduced when bdrv_iterate() was removed. > > >=20 > > > Change that by skipping only empty devices. > > >=20 > > > Cc: Markus Armbruster > > > Suggested: Kevin Wolf > > > Fixes: fea68bb6e9fa ("block: Eliminate bdrv_iterate(), use bdrv_next(= )") > >=20 > > It's not clear to me that fea68bb6e9fa introduced the bug. The code is > > still <=3D 0 there and I don't see anything else that skips empty devic= es. > > Can you explain the bug in fea68bb6e9fa? >=20 > Let me try. Initially, the code was : > static void init_blk_migration_it(void *opaque, BlockDriverState *bs) > { > BlockDriverState *bs; > BlkMigDevState *bmds; > int64_t sectors; > if (!bdrv_is_read_only(bs)) { > sectors =3D bdrv_nb_sectors(bs); > if (sectors <=3D 0) { > return; > ... > } > =09 > static void init_blk_migration(QEMUFile *f) > { > block_mig_state.submitted =3D 0; > block_mig_state.read_done =3D 0; > block_mig_state.transferred =3D 0; > block_mig_state.total_sector_sum =3D 0; > block_mig_state.prev_progress =3D -1; > block_mig_state.bulk_completed =3D 0; > block_mig_state.zero_blocks =3D migrate_zero_blocks(); > bdrv_iterate(init_blk_migration_it, NULL); > } >=20 > bdrv_iterate() was iterating on all devices and exiting one iteration > early if the device was empty or an error detected. The loop applied > on all devices always, only empty devices and the ones with a failure > were skipped. > It was replaced by : >=20 > static void init_blk_migration(QEMUFile *f) > { > BlockDriverState *bs; > BlkMigDevState *bmds; > int64_t sectors; > block_mig_state.submitted =3D 0; > block_mig_state.read_done =3D 0; > block_mig_state.transferred =3D 0; > block_mig_state.total_sector_sum =3D 0; > block_mig_state.prev_progress =3D -1; > block_mig_state.bulk_completed =3D 0; > block_mig_state.zero_blocks =3D migrate_zero_blocks(); > for (bs =3D bdrv_next(NULL); bs; bs =3D bdrv_next(bs)) { > if (bdrv_is_read_only(bs)) { > continue; > } > sectors =3D bdrv_nb_sectors(bs); > if (sectors <=3D 0) { > return; > =09 > ... > } >=20 > The loop and function exit at first failure or first empty device, > skipping the remaining devices. This is a different behavior. >=20 > What we would want today is ignore empty devices, as it done for > the read only ones, return at first failure and let the caller of > init_blk_migration() report. >=20 > This is a short term fix for 9.0 because the block migration code > is deprecated and should be removed in 9.1. I understand now. I missed that returning from init_blk_migration_it() did not abort iteration. Thank you! 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