From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BC79F606A33D for ; Tue, 3 Nov 2026 10:02:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=My83eZb1 Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xOBLY-0002H3-HV; Tue, 03 Nov 2026 05:02:28 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xOBLW-0002Gd-A2 for qemu-devel@nongnu.org; Tue, 03 Nov 2026 05:02:26 -0500 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 1xOBLU-000563-Jj for qemu-devel@nongnu.org; Tue, 03 Nov 2026 05:02:26 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1793700143; 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=JnW2vvaIDI9r7/GXha8d6tGjVCdRhCcTcetPJE08iwA=; b=My83eZb1XwfMllVtGYHKt2WWwXhqINCB1bgAQ2kDZOHQPrNma/w3jE5hxq2JaA1Z3F2XMN sGGnDn0C/k9K1AeSmG1cWmX9nUM+VKzYMtzzZW3DWSD5sZFWdtyPp4ljgPO60F3ry862ey ngZg9VyQZK37bMVgbQHpAvANrjAJ9RI= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-619-ukBy6l_EP6y2NoApGKPaFg-1; Tue, 03 Nov 2026 05:02:21 -0500 X-MC-Unique: ukBy6l_EP6y2NoApGKPaFg-1 X-Mimecast-MFC-AGG-ID: ukBy6l_EP6y2NoApGKPaFg_1793700140 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7D9E91955BDC; Tue, 3 Nov 2026 10:02:20 +0000 (UTC) Received: from redhat.com (unknown [10.44.48.52]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 49C2B180029C; Tue, 3 Nov 2026 10:02:19 +0000 (UTC) Date: Tue, 3 Nov 2026 11:02:16 +0100 From: Kevin Wolf To: "Denis V. Lunev" Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org Subject: Re: [PATCH 1/4] block: notify the parent when a replaced child has a different size Message-ID: References: <20260812121500.1034178-1-den@openvz.org> <20260812121500.1034178-2-den@openvz.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260812121500.1034178-2-den@openvz.org> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 5 X-Spam_score: 0.5 X-Spam_bar: / X-Spam_report: (0.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Archive: List-Post: List-Help: List-Subscribe: , Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Am 12.08.2026 um 14:14 hat Denis V. Lunev geschrieben: > bdrv_replace_child_bs() swaps the node a BdrvChild points to without > telling the parent anything about it, so a parent which tracks the size of > its child never learns that it changed. Every other way the size of a node > changes goes through bdrv_co_truncate(), which does notify. > > The device models which care all register the same BlockDevOps hook: > > virtio-blk resize_cb = virtio_blk_resize(), ending up in > virtio_notify_config() > ide/ahci resize_cb = ide_resize_cb(), refreshing the cached size > and the IDENTIFY data > scsi-disk resize_cb = scsi_disk_resize_cb(), reporting > CAPACITY DATA HAS CHANGED > xen-block resize_cb = xen_block_resize_cb() > > Only scsi-disk is really hurt by the missing notification, because it is > the one which validates guest requests against a cached size. > virtio_blk_sect_range_ok() and ide_sect_range_ok() both call > blk_get_geometry() for every request, so a missing notification leaves > those guests with a stale idea of the size but never refuses I/O which the > node underneath can serve. check_lba_range() compares against > SCSIDevice.max_lba, filled in by scsi_disk_reset() and updated only by the > READ CAPACITY(10) and (16) handlers, so with nothing to make the guest > re-read the capacity every request past the end of the old node is refused > for the whole life of the device. > > This is reachable with qom-set of the 'drive' property, which is allowed > on a realized device, and it is silent on the host: out-of-range requests > are answered by scsi_check_condition() and never reach > scsi_handle_rw_error(), so there is no BLOCK_IO_ERROR event and io-status > stays 'ok'. The guest sees ILLEGAL REQUEST / LOGICAL BLOCK ADDRESS OUT OF > RANGE, which Linux turns into EREMOTEIO for reads as well as writes. > > Emit the notification from bdrv_replace_child_bs(), so that every device > model gets it through the path it already implements rather than any of > them being special cased. Send it only when the size really changed, which > keeps the callback out of the common case of a replacement by an equally > sized node. > > Signed-off-by: Denis V. Lunev > --- > block.c | 13 +++++++++++++ > include/block/block_int-io.h | 3 +++ > 2 files changed, 16 insertions(+) > > diff --git a/block.c b/block.c > index f0a6042e61..1fe66caf8d 100644 > --- a/block.c > +++ b/block.c > @@ -5524,9 +5524,12 @@ int bdrv_replace_child_bs(BdrvChild *child, BlockDriverState *new_bs, > Transaction *tran = tran_new(); > g_autoptr(GSList) refresh_list = NULL; > BlockDriverState *old_bs = child->bs; > + int64_t old_len; > > GLOBAL_STATE_CODE(); > > + old_len = bdrv_getlength(old_bs); > + > bdrv_ref(old_bs); > bdrv_drained_begin(old_bs); > bdrv_drained_begin(new_bs); bdrv_drained_begin() involves nested event loops. Can't old_len become stale here? It would feel safer to query it after draining. > @@ -5542,6 +5545,16 @@ int bdrv_replace_child_bs(BdrvChild *child, BlockDriverState *new_bs, > tran_finalize(tran, ret); > > bdrv_graph_wrunlock(); > + > + /* A parent caching the child size has to learn that it changed */ > + if (ret == 0) { > + int64_t new_len = bdrv_getlength(new_bs); > + > + if (new_len >= 0 && new_len != old_len) { > + bdrv_parent_cb_resize(new_bs); This notifies other parents of the new node as well even though nothing changed for them. Especially since you already query old_len/new_len to avoid unnecessary notifications, we should probably call only child->klass->resize(child) through a coroutine wrapper here to notify only the BdrvChild that we actually changed. > + } > + } > + > bdrv_drained_end(old_bs); > bdrv_drained_end(new_bs); > bdrv_unref(old_bs); Kevin