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 7925CC25B78 for ; Mon, 13 May 2024 13:25:04 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1s6VfQ-0003eL-K6; Mon, 13 May 2024 09:24:36 -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 1s6VfO-0003e4-7l; Mon, 13 May 2024 09:24:34 -0400 Received: from proxmox-new.maurer-it.com ([94.136.29.106]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1s6VfM-0004vi-3n; Mon, 13 May 2024 09:24:33 -0400 Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id AC61247E68; Mon, 13 May 2024 15:24:29 +0200 (CEST) Message-ID: <1acd096c-5ec9-411d-b06e-cd64fb898852@proxmox.com> Date: Mon, 13 May 2024 15:24:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] copy-before-write: allow specifying minimum cluster size To: Markus Armbruster Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, eblake@redhat.com, hreitz@redhat.com, kwolf@redhat.com, vsementsov@yandex-team.ru, jsnow@redhat.com References: <20240308155158.830258-1-f.ebner@proxmox.com> <20240308155158.830258-2-f.ebner@proxmox.com> <875xx9s6pp.fsf@pond.sub.org> Content-Language: en-US From: Fiona Ebner In-Reply-To: <875xx9s6pp.fsf@pond.sub.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=94.136.29.106; envelope-from=f.ebner@proxmox.com; helo=proxmox-new.maurer-it.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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 Am 26.03.24 um 10:06 schrieb Markus Armbruster: >> @@ -365,7 +368,13 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target, >> >> GLOBAL_STATE_CODE(); >> >> - cluster_size = block_copy_calculate_cluster_size(target->bs, errp); >> + if (min_cluster_size && !is_power_of_2(min_cluster_size)) { > > min_cluster_size is int64_t, is_power_of_2() takes uint64_t. Bad if > min_cluster_size is negative. Could this happen? > No, because it comes in as a uint32_t via the QAPI (the internal caller added by patch 2/2 from the backup code also gets the value via QAPI and there uint32_t is used too). ---snip--- >> diff --git a/qapi/block-core.json b/qapi/block-core.json >> index 0a72c590a8..85c8f88f6e 100644 >> --- a/qapi/block-core.json >> +++ b/qapi/block-core.json >> @@ -4625,12 +4625,18 @@ >> # @on-cbw-error parameter will decide how this failure is handled. >> # Default 0. (Since 7.1) >> # >> +# @min-cluster-size: Minimum size of blocks used by copy-before-write >> +# operations. Has to be a power of 2. No effect if smaller than >> +# the maximum of the target's cluster size and 64 KiB. Default 0. >> +# (Since 9.0) >> +# >> # Since: 6.2 >> ## >> { 'struct': 'BlockdevOptionsCbw', >> 'base': 'BlockdevOptionsGenericFormat', >> 'data': { 'target': 'BlockdevRef', '*bitmap': 'BlockDirtyBitmap', >> - '*on-cbw-error': 'OnCbwError', '*cbw-timeout': 'uint32' } } >> + '*on-cbw-error': 'OnCbwError', '*cbw-timeout': 'uint32', >> + '*min-cluster-size': 'uint32' } } > > Elsewhere in the schema, we use either 'int' or 'size' for cluster-size. > Why the difference? > The motivation was to disallow negative values up front and have it work with block_copy_calculate_cluster_size(), whose result is an int64_t. If I go with 'int', I'll have to add a check to disallow negative values. If I go with 'size', I'll have to add a check for to disallow too large values. Which approach should I go with? Best Regards, Fiona