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 lists1p.gnu.org (lists1p.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 B7DCCCD6E4A for ; Tue, 2 Jun 2026 11:30:15 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wUNJL-00075r-DB; Tue, 02 Jun 2026 07:29:31 -0400 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 1wUNJJ-00075b-M8 for qemu-devel@nongnu.org; Tue, 02 Jun 2026 07:29:29 -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 1wUNJH-0006oU-Kg for qemu-devel@nongnu.org; Tue, 02 Jun 2026 07:29:29 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1780399765; 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=HFFNqVI0xx0YjPZMcRanRS9Sr9Q0CDAJLAv9+v8Tmmk=; b=WJYfaPbLAzlWPC5PEPU9C9KLj2qZZgisFA7AdLC3SQmTn4ORQQMQUlFyxBMQKU2jONDggR SSNnsbkw50l3PvXasbkYOOtDzRuHY6YkKG5+jZmHTNpVHSgKFkg334b547UVGS7nLfIt65 TFlzyb7w4IpcDKmAqg/dv8S4ptxeem0= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-447-pdLoYHvFNeqR06E7baSU4g-1; Tue, 02 Jun 2026 07:29:24 -0400 X-MC-Unique: pdLoYHvFNeqR06E7baSU4g-1 X-Mimecast-MFC-AGG-ID: pdLoYHvFNeqR06E7baSU4g_1780399763 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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 17C7C1800367; Tue, 2 Jun 2026 11:29:23 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.2]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 175BE30002DD; Tue, 2 Jun 2026 11:29:22 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id A261821E6A01; Tue, 02 Jun 2026 13:29:19 +0200 (CEST) From: Markus Armbruster To: Zhang Chen Cc: qemu-devel , "Dr . David Alan Gilbert" , Eric Blake , Markus Armbruster , "Michael S . Tsirkin" , Stefan Hajnoczi Subject: Re: [PATCH V8 02/15] iothread: introduce iothread_ref/unref to track attached devices In-Reply-To: <20260529213321.96271-3-zhangckid@gmail.com> (Zhang Chen's message of "Sat, 30 May 2026 05:33:08 +0800") References: <20260529213321.96271-1-zhangckid@gmail.com> <20260529213321.96271-3-zhangckid@gmail.com> Date: Tue, 02 Jun 2026 13:29:19 +0200 Message-ID: <87tsrl2nao.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain 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: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, 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, SPF_HELO_PASS=-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: 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: > Currently, IOThreads do not maintain a record of which devices are > associated with them. This makes it difficult to monitor the > workload distribution of IOThreads, especially in complex > hotplug scenarios involving multiple virtio-blk or virtio-scsi devices. > > This patch introduces a reference counting and tracking mechanism > within the IOThread object: > > - iothread_ref(): Prepends the device's IOThreadHolder to a list. > - iothread_unref(): Searches for the IOThreadHolder using a custom > string comparison (g_strcmp0), releases the associated memory > upon a successful match. > - holders: A GList storing the IOThreadHolder of attached devices > for runtime introspection. > > A later commit will add QMP commands to let management applications > query the attachment status of IOThreads. > > Signed-off-by: Zhang Chen > --- > include/system/iothread.h | 5 +++ > iothread.c | 94 +++++++++++++++++++++++++++++++++++++++ > qapi/misc.json | 61 +++++++++++++++++++++++++ > 3 files changed, 160 insertions(+) > > diff --git a/include/system/iothread.h b/include/system/iothread.h > index a1ef7696cb..b9207ad829 100644 > --- a/include/system/iothread.h > +++ b/include/system/iothread.h > @@ -50,6 +50,11 @@ struct IOThread { > bool stopping; /* has iothread_stop() been called? */ > bool running; /* should iothread_run() continue? */ > int thread_id; > + /* > + * The list elements are of type IOThreadHolder, which can > + * represent either a QOM path or a block node name. You forgot monitors. Suggest "which can either be a QOM object, a block node, or a monitor." > + */ > + GList *holders; > > /* AioContext poll parameters */ > int64_t poll_max_ns; > diff --git a/iothread.c b/iothread.c > index 3558535b40..3301b8d495 100644 > --- a/iothread.c > +++ b/iothread.c > @@ -25,6 +25,92 @@ > #include "qemu/rcu.h" > #include "qemu/main-loop.h" > > +/* > + * iothread_ref: > + * @iothread: the iothread to track > + * @holder: the IOThreadHolder object initialized by the caller > + * > + * Add the @holder to the iothread's tracking list. > + */ > +static void iothread_ref(IOThread *iothread, const IOThreadHolder *holder) Yes, this is the interface I want :) > +{ > + assert(holder); > + IOThreadHolder *h = g_new0(IOThreadHolder, 1); > + > + h->type = holder->type; > + switch (holder->type) { > + case IO_THREAD_HOLDER_KIND_QOM_OBJECT: > + h->u.qom_object.qom_path = g_strdup(holder->u.qom_object.qom_path); > + break; > + case IO_THREAD_HOLDER_KIND_BLOCK_NODE: > + h->u.block_node.node_name = > + g_strdup(holder->u.block_node.node_name); > + break; > + case IO_THREAD_HOLDER_KIND_MONITOR_NAME: > + h->u.monitor_name.monitor_name = > + g_strdup(holder->u.monitor_name.monitor_name); > + break; > + default: > + g_assert_not_reached(); > + } This makes @h a deep copy of @holder. Try IOThreadHolder *h = QAPI_CLONE(IOThreadHolder, holder); instead. Instead of making a copy, the function could take ownership of @holder, and require @holder's members to be dynamically allocated. More efficient, but complicates the callers somewhat. Not worthwhile, I guess. > + > + iothread->holders = g_list_prepend(iothread->holders, h); > +} > + > +static int iothread_holder_compare(gconstpointer a, gconstpointer b) > +{ > + const IOThreadHolder *holder_a = a; > + const IOThreadHolder *holder_b = b; > + const char *name_a, *name_b; > + > + if (holder_a->type != holder_b->type) { > + return -1; Please use return holder_b->type - holder_a->type; Why? By convention, an int-valued function fn() comparing A to B returns less than 0 when AB. Anything else needs a prominent comment. Best to stick to the convention whenever practical. Since A < B iff B > A, we want fn(A, B) == -fn(B, A). Your function does not satisfy that! Harmless for now, because you only ever pass it to g_list_find_custom(), which treats all non-zero values the same. But if anyone passes it to something like qsort() in the future, they can look forward to some debugging "fun". > + } > + > + switch (holder_a->type) { > + case IO_THREAD_HOLDER_KIND_QOM_OBJECT: > + name_a = holder_a->u.qom_object.qom_path; > + name_b = holder_b->u.qom_object.qom_path; > + break; > + case IO_THREAD_HOLDER_KIND_BLOCK_NODE: > + name_a = holder_a->u.block_node.node_name; > + name_b = holder_b->u.block_node.node_name; > + break; > + case IO_THREAD_HOLDER_KIND_MONITOR_NAME: > + name_a = holder_a->u.monitor_name.monitor_name; > + name_b = holder_b->u.monitor_name.monitor_name; > + break; > + default: > + /* > + * This should not happen. If it does, name_a/b remains > + * NULL and g_strcmp0 will handle it safely. > + */ > + name_a = NULL; > + name_b = NULL; Replace this by g_assert_not_reached(); Then neither @name_a nor @name_b can be null, because a non-optional QAPI str is never null. Simply use strcmp(). > + } > + > + return g_strcmp0(name_a, name_b); > +} > + > +/* > + * This function removes the @holder from the @iothread's tracking list. > + * The @holder must match the one used previously in iothread_ref(). > + * It is a programming error to call this with a @holder that is not > + * currently associated with the @iothread. > + */ > +static void iothread_unref(IOThread *iothread, const IOThreadHolder *holder) > +{ > + assert(holder); > + GList *link = g_list_find_custom(iothread->holders, holder, > + (GCompareFunc)iothread_holder_compare); > + > + assert(link); > + > + IOThreadHolder *h = (IOThreadHolder *)link->data; > + qapi_free_IOThreadHolder(h); > + iothread->holders = g_list_delete_link(iothread->holders, link); Removing @link from the list before freeing link->data would be more obviously correct, wouldn't it? > +} > + > static void *iothread_run(void *opaque) > { > IOThread *iothread = opaque; > @@ -356,6 +442,14 @@ char *iothread_get_id(IOThread *iothread) > > AioContext *iothread_get_aio_context(IOThread *iothread) > { > + /* Remove in next patch for build */ > + IOThreadHolder holder = { > + .type = IO_THREAD_HOLDER_KIND_QOM_OBJECT, > + .u.qom_object.qom_path = (char *)"tmp_path", > + }; > + iothread_ref(iothread, &holder); > + iothread_unref(iothread, &holder); > + Is this really needed to make this patch work? > return iothread->ctx; > } > > diff --git a/qapi/misc.json b/qapi/misc.json > index c71a5fe657..d9f82f0922 100644 > --- a/qapi/misc.json > +++ b/qapi/misc.json > @@ -67,6 +67,67 @@ > ## > { 'command': 'query-name', 'returns': 'NameInfo', 'allow-preconfig': true } > > + > +## > +# @IOThreadHolderBlockNode: > +# > +# @node-name: A block node. Let's use # @node-name: Name of the block node to make it more similar to node-name descriptions elsewhere. > +# > +# Since: 11.1 > +# > +## > +{ 'struct': 'IOThreadHolderBlockNode', > + 'data': { 'node-name': 'str' } } > + > +## > +# @IOThreadHolderQomObject: > +# > +# @qom-path: A QOM Object. Likewise, let's use # @qom-path: Path to the object in the QOM tree > +# > +# Since: 11.1 > +# > +## > +{ 'struct': 'IOThreadHolderQomObject', > + 'data': { 'qom-path': 'str' } } > + > +## > +# @IOThreadHolderMonitor: > +# Let's use # @monitor-name: Name of the HMP/QMP monitor > +# @monitor-name: A HMP/QMP monitor. > +# > +# Since: 11.1 > +# > +## > +{ 'struct': 'IOThreadHolderMonitor', > + 'data': { 'monitor-name': 'str' } } > + > +## > +# @IOThreadHolderKind: > +# > +# @block-node: A block node. > +# @qom-object: A QOM Object. > +# @monitor-name: A HMP/QMP monitor. Rename to @monitor for consistency with the other two. Remark, not a request to change anything in your patch: kind monitor will become obsolete when monitors become QOM objects. Doing that before we release this interface is desirable. > +# > +# Since: 11.1 > +## > +{ 'enum': 'IOThreadHolderKind', > + 'data': [ 'block-node', 'qom-object', 'monitor-name' ] } > + > +## > +# @IOThreadHolder: > +# Let's add a short description: # The block node, QOM object, or monitor holding the I/O thread. > +# @type: the kind of I/O thread holder. > +# > +# Since: 11.1 > +## > +{ 'union': 'IOThreadHolder', > + 'base': { 'type': 'IOThreadHolderKind' }, > + 'discriminator': 'type', > + 'data': { > + 'block-node': 'IOThreadHolderBlockNode', > + 'qom-object': 'IOThreadHolderQomObject', > + 'monitor-name': 'IOThreadHolderMonitor' } } > + > ## > # @IOThreadInfo: > #