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 D18A6FF60C2 for ; Tue, 31 Mar 2026 05:55:06 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1w7S3v-0003ps-1a; Tue, 31 Mar 2026 01:54:51 -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 1w7S3t-0003pT-EO for qemu-devel@nongnu.org; Tue, 31 Mar 2026 01:54:49 -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 1w7S3r-0000dz-Jh for qemu-devel@nongnu.org; Tue, 31 Mar 2026 01:54:49 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1774936487; 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:resent-to: resent-from:resent-message-id:in-reply-to:in-reply-to: references:references; bh=rk3QYWDM+EmYXI5eH/NLPACn/AKB5G+ypw/DwjSqC1w=; b=dXZiz4UcETkwIcbrAikRdfULbrHB7g7FW7yGEGUpJXryJZp+GjTP93rZ88gSkUIUeQAGAB AeFNAGnA9D9CMbEt99XLwYlAwGm5D8euGDSsXbu9aEmHn6pmvTaVYwpl4nGUVnkJ9HHSCQ brdwsKeX/y4rDXUPMwABAiX1D/fsIW0= 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-192-e4RuFbsrP1C6F-9-qJ_6Ug-1; Tue, 31 Mar 2026 01:54:41 -0400 X-MC-Unique: e4RuFbsrP1C6F-9-qJ_6Ug-1 X-Mimecast-MFC-AGG-ID: e4RuFbsrP1C6F-9-qJ_6Ug_1774936480 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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E9F2319560A1; Tue, 31 Mar 2026 05:54:39 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.6]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 60A4D1800107; Tue, 31 Mar 2026 05:54:39 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id CFC1821E6A28; Tue, 31 Mar 2026 07:54:36 +0200 (CEST) Resent-To: stefanha@gmail.com, zhangckid@gmail.com, qemu-devel@nongnu.org, dave@treblig.org Resent-From: Markus Armbruster Resent-Date: Tue, 31 Mar 2026 07:54:36 +0200 Resent-Message-ID: <87zf3ownkz.fsf@pond.sub.org> From: Markus Armbruster To: Zhang Chen Cc: Stefan Hajnoczi , Kevin Wolf , Hanna Czenczek , Stefan Hajnoczi , qemu-devel , "Dr . David Alan Gilbert" , Eric Blake , "Michael S . Tsirkin" Subject: Re: [PATCH V5 04/13] blockdev: Update tracking iothread users with holder name In-Reply-To: (Zhang Chen's message of "Mon, 30 Mar 2026 11:13:26 +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> <87jyv9fyn5.fsf@pond.sub.org> Date: Mon, 30 Mar 2026 11:02:03 +0200 Message-ID: <875x6dzo50.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 10.30.177.93 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 27 X-Spam_score: 2.7 X-Spam_bar: ++ X-Spam_report: (2.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.54, 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_H2=-0.01, RCVD_IN_SBL_CSS=3.335, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=1, RCVD_IN_VALIDITY_RPBL_BLOCKED=1, 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 Wed, Mar 18, 2026 at 5:13=E2=80=AFPM Stefan Hajnoczi wrote: >> >> On Wed, Mar 18, 2026 at 2:20=E2=80=AFPM Markus Armbruster wrote: >> > >> > 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 ma= in loop >> > >> # >> > >> # @force: true if the node and its children should be moved whe= n 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(cons= t char *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 un= defined >> > >> >> > behavior and may crash. >> > >> >> > >> Yes. >> > >> >> > >> >> > node_name is unique across block driver graph nodes and could = be used. >> > >> >> > 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 the= re can be >> > >> >> > no collisions between QOM paths and block driver graph nodes. >> > >> >> > >> I guess you're talking about the values that go into IOThreadInfo m= ember >> > >> holders. From PATCH 13: >> > >> >> > >> # @holders: The parameter is an array of QOM paths indicating h= ow many >> > >> # 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 pers= istent >> > >> # thread pool. When a device is hot-unplugged, the corresp= onding >> > >> # IOThread is released but remains available, allowing subs= equent >> > >> # hot-plugged devices to attach to and reuse the existing t= hread. >> > >> # 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("BlockDriverStat= e %s", node_name); >> > >> >> > >> > >> >> > (A cleaner long-term solution would be making BlockDriverState= s 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 mentione= d in >> > >> >> patch 7 and 9. >> > >> > >> > >> > A thought about the QAPI interface: >> > >> > >> > >> > QAPI expresses as much information in the schema as possible, so = I think >> > >> > 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 Objec= t paths >> > >> > vs block node-names. Let's avoid having a single string value tha= t takes >> > >> > 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 Q= OM >> > >> path and block node name. >> > >> >> > >> Complex semantics tend to require more complex documentation. >> > >> >> > >> Which choice is better depends on the specific case. I generally l= ean >> > >> 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. >> >> It may be a lot of work. An alternative I suggested was a holder enum >> instead of a string so that QOM paths and block node names can be >> separated with no chance of collisions. That approach is more >> straightforward to implement and the main drawback I see is that the >> enum would become superfluous if block nodes become QOM objects in the >> future. That's not terrible. >> >> Stefan > > Ping.... > > Hi Markus and Stefan, > As Markus's comments, I prefer the /blockdevs or /block-nodes is more sim= ple, > And use a holder enum instead of a string will make it more difficult > for users to understand. > Please let us make a decision. I'm not sure what exactly you need from me. I assume you need advice on how to represent a reference to a "holder" in the QAPI schema, where the holder can either be a QOM object or a block node. If everthing was a QOM object, we could simply use a QOM path, i.e. 'str'. Sadly, block nodes are not QOM objects. Unless you want to solve the (non-trivial) problem of making them QOM objects first, you need something else. My recommendation for something else would be a union: { 'union': 'IoThreadHolder', 'base': { 'type': 'IoThreadHolderKind' }, 'discriminator': 'type', 'data': { 'block-node': ..., 'qom-object': ... } } Stefan, do you agree? Hope this helps! > Hi Kevin and Hanna, > Considering the possibility of blockdevs being qom in the future, we > need your idea here, any comments for the series? > > Thanks > Chen