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 2AF25FCD0BF for ; Wed, 18 Mar 2026 06:19:50 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1w2kFa-00038p-Jt; Wed, 18 Mar 2026 02:19:26 -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 1w2kFX-00036o-AH for qemu-devel@nongnu.org; Wed, 18 Mar 2026 02:19:23 -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 1w2kFT-00076k-La for qemu-devel@nongnu.org; Wed, 18 Mar 2026 02:19:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1773814758; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Nyry6HRSfyal5LU6pTpe3CHqKuNRW0NKKEFjDJ2OaP0=; b=bwR4xZ4IORiY0lUn0G6/u/RCdbP9jnH1L2JwtNP2yJtxTA0hATIGb5TPar5Ce5KQH0GZGP QWqOGn3r+enXj4LAwYXBKR7v1p8e3SAxYm3BHsJaX+uXlCmj4piQo3HgcvIyNa/GZe7Kua Q+ouIse9TFO/6T4sTawoZ4EVP3UORdI= Received: from mx-prod-mc-01.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-659-Y5GCceEEMw-Ct4YSqsPBGA-1; Wed, 18 Mar 2026 02:19:14 -0400 X-MC-Unique: Y5GCceEEMw-Ct4YSqsPBGA-1 X-Mimecast-MFC-AGG-ID: Y5GCceEEMw-Ct4YSqsPBGA_1773814753 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7673B19560AE; Wed, 18 Mar 2026 06:19:13 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.6]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A58B030001A1; Wed, 18 Mar 2026 06:19:12 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 45FEE21E6937; Wed, 18 Mar 2026 07:19:10 +0100 (CET) From: Markus Armbruster To: Zhang Chen Cc: Stefan Hajnoczi , Kevin Wolf , qemu-devel , "Dr . David Alan Gilbert" , Eric Blake , "Michael S . Tsirkin" , Hanna Czenczek Subject: Re: [PATCH V5 04/13] blockdev: Update tracking iothread users with holder name In-Reply-To: (Zhang Chen's message of "Tue, 17 Mar 2026 21:25:06 +0800") References: <20260305142459.52559-1-zhangckid@gmail.com> <20260305142459.52559-5-zhangckid@gmail.com> <20260309081502.GC39949@fedora> <20260312052422.GA116604@fedora> <87bjgtxv9b.fsf@pond.sub.org> Date: Wed, 18 Mar 2026 07:19:10 +0100 Message-ID: <87jyv9fyn5.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -3 X-Spam_score: -0.4 X-Spam_bar: / X-Spam_report: (-0.4 / 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_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.819, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.903, 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-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 Zhang Chen writes: > On Thu, Mar 12, 2026 at 5:16=E2=80=AFPM Markus Armbruster wrote: >> >> Context... we're talking about this command: >> >> ## >> # @x-blockdev-set-iothread: >> # >> # Move @node and its children into the @iothread. If @iothread is >> # null then move @node and its children into the main loop. >> # >> # The node must not be attached to a BlockBackend. >> # >> # @node-name: the name of the block driver node >> # >> # @iothread: the name of the IOThread object or null for the main lo= op >> # >> # @force: true if the node and its children should be moved when a >> # BlockBackend is already attached >> # >> # Features: >> # >> # @unstable: This command is experimental and intended for test cases >> # that need control over IOThreads only. >> # >> # Since: 2.12 >> # >> # .. qmp-example:: >> # :title: Move a node into an IOThread >> # >> # -> { "execute": "x-blockdev-set-iothread", >> # "arguments": { "node-name": "disk1", >> # "iothread": "iothread0" } } >> # <- { "return": {} } >> # >> # .. qmp-example:: >> # :title: Move a node into the main loop >> # >> # -> { "execute": "x-blockdev-set-iothread", >> # "arguments": { "node-name": "disk1", >> # "iothread": null } } >> # <- { "return": {} } >> ## >> { 'command': 'x-blockdev-set-iothread', >> 'data' : { 'node-name': 'str', >> 'iothread': 'StrOrNull', >> '*force': 'bool' }, >> 'features': [ 'unstable' ], >> 'allow-preconfig': true } >> >> >> Stefan Hajnoczi writes: >> >> > On Tue, Mar 10, 2026 at 06:02:54PM +0800, Zhang Chen wrote: >> >> On Mon, Mar 9, 2026 at 4:15=E2=80=AFPM Stefan Hajnoczi wrote: >> >> > >> >> > On Thu, Mar 05, 2026 at 10:24:50PM +0800, Zhang Chen wrote: >> >> > > Update the usage of "iothread_get_aio_context()". >> >> > > >> >> > > Signed-off-by: Zhang Chen >> >> > > --- >> >> > > blockdev.c | 9 ++++++++- >> >> > > 1 file changed, 8 insertions(+), 1 deletion(-) >> >> > > >> >> > > diff --git a/blockdev.c b/blockdev.c >> >> > > index 6e86c6262f..01ccf64b3f 100644 >> >> > > --- a/blockdev.c >> >> > > +++ b/blockdev.c >> >> > > @@ -3683,7 +3683,14 @@ void qmp_x_blockdev_set_iothread(const cha= r *node_name, StrOrNull *iothread, >> >> > > goto out; >> >> > > } >> >> > > >> >> > > - new_context =3D iothread_get_aio_context(obj); >> >> > > + char *path =3D object_get_canonical_path(OBJECT(bs)); >> >> > >> >> > CCing Kevin and Markus in case they have an opinion on this. >> >> > >> >> > BlockDriverState is not a QOM Object so using OBJECT(bs) is undefin= ed >> >> > behavior and may crash. >> >> Yes. >> >> >> > node_name is unique across block driver graph nodes and could be us= ed. >> >> > Unfortunately it's not connected to the QOM Object hierarchy. >> >> Correct. >> >> >> > Maybe= it's >> >> > best to build a holder name that is an invalid QOM path so there ca= n be >> >> > no collisions between QOM paths and block driver graph nodes. >> >> I guess you're talking about the values that go into IOThreadInfo member >> holders. From PATCH 13: >> >> # @holders: The parameter is an array of QOM paths indicating how ma= ny >> # active devices are currently associated with this iothread >> # (e.g. virtio-blk). In hotplug scenarios, users can >> # pre-allocate multiple iothread objects to serve as a persistent >> # thread pool. When a device is hot-unplugged, the corresponding >> # IOThread is released but remains available, allowing subsequent >> # hot-plugged devices to attach to and reuse the existing thread. >> # Returns empty if no devices are attached. (since 11.0) >> # >> >> I further guess you need it to refer to both QOM objects and block >> nodes, and you worry about ambiguity. >> >> Ambiguity indeed exists: a block node name can be a valid QOM path. >> >> We could restrict QOM paths to absolute paths. These start with '/'. >> If I remember correctly, node names cannot contain '/'. >> >> Note that canonical paths (returned object_get_canonical_path()) are >> absolute. >> >> We ran into a similar design issue in review of Vladimir's "[PATCH v10 >> 4/8] qapi: add blockdev-replace command" not too long ago: >> >> Subject: Re: [PATCH v10 4/8] qapi: add blockdev-replace command >> Date: Wed, 04 Feb 2026 13:26:35 +0100 >> Message-ID: <87wm0sy9s4.fsf@pond.sub.org> >> >> There, the new command needs to refer to QOM object, block node, or >> block export. >> >> >> > g_autofree char *holder =3D g_strdup_printf("BlockDriverState %s"= , node_name); >> >> > >> >> > (A cleaner long-term solution would be making BlockDriverStates QOM >> >> > Objects so they have a proper path.) >> >> Yes, but that's a beefy project, isn't it? >> >> >> If no other comments, it's OK for me. This issue like I mentioned in >> >> patch 7 and 9. >> > >> > A thought about the QAPI interface: >> > >> > QAPI expresses as much information in the schema as possible, so I thi= nk >> > the right approach would be a {'union': 'IOThreadHolder', >> > 'discriminator': 'type', ...} that supports at least "qom" and >> > "block-node". That way there are proper types to encode QOM Object pat= hs >> > vs block node-names. Let's avoid having a single string value that tak= es >> > on different meaning depending on the type of holder. >> >> This shifts the complexity from semantics to syntax. >> >> Semantics: the member can have multiple meanings, and you have to >> examine its value to decide which one applies. The member's >> documentation should specify how to decide. Say something like "if the >> value starts with '/', it's an absolute QOM path, else it's a block node >> name". >> >> Syntax: meaning is syntactically obvious. For instance, union of QOM >> path and block node name. >> >> Complex semantics tend to require more complex documentation. >> >> Which choice is better depends on the specific case. I generally lean >> towards syntax. >> > > I agree Markus's suggestion. > Compare with standard QOM path: > /machine/peripheral/blk0/virtio-backend > > I will try to implement block nodes path like this: > /machine/blockdriverstate/node-name I gather you'd like to try creating QOM objects for block nodes. First, this should not go into /machine. We already have /chardevs and /audiodevs, which suggests something like /blockdevs or /block-nodes. Second, QOMifying block nodes feels ambitious to me. Please discuss it with block maintainers Kevin and Hanna. > And Markus, could you please take a look at patch 13? > I will prepare the V6 after your comments. Done. It may need an update for changes made here, though.