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 C3741E6E815 for ; Wed, 4 Feb 2026 06:12:37 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vnW7K-0003hY-Az; Wed, 04 Feb 2026 01:12:00 -0500 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 1vnW7H-0003h4-RP for qemu-devel@nongnu.org; Wed, 04 Feb 2026 01:11:56 -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 1vnW7F-00053D-CM for qemu-devel@nongnu.org; Wed, 04 Feb 2026 01:11:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1770185511; 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=LdBC23U37EdSZCt5wdSJ5+ZnPxLMJ66ATpqb7N4z2dg=; b=AnmW2oAgIm5vBXqBv4cnvKErpfbQlc3sXu3cbT11PKuQfBQRSji+jW7bZ6YIpLqbTt/TkQ kEhOSpYHXz5RvF3D+GSNs1z85Dd5sZ+Rx5nPFbRsOgpgw57W2ewVUDe8yop5HpfDgID7Hk PhRDNyns6zIZUMgPheW/WA75bYBUg24= 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-149-E65V6q9mOJ-lLF8VnbwJPg-1; Wed, 04 Feb 2026 01:11:49 -0500 X-MC-Unique: E65V6q9mOJ-lLF8VnbwJPg-1 X-Mimecast-MFC-AGG-ID: E65V6q9mOJ-lLF8VnbwJPg_1770185508 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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 AE52019560B7; Wed, 4 Feb 2026 06:11:47 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.22]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3293818003F5; Wed, 4 Feb 2026 06:11:47 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 9F41321E692D; Wed, 04 Feb 2026 07:11:44 +0100 (CET) From: Markus Armbruster To: Peter Krempa Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Kevin Wolf , Hanna Reitz , Eric Blake Subject: Re: [PATCH v3 1/2] block: Wire up 'flat' mode also for 'query-block' In-Reply-To: (Peter Krempa's message of "Tue, 3 Feb 2026 16:17:22 +0100") References: <87pl6m2g02.fsf@pond.sub.org> Date: Wed, 04 Feb 2026 07:11:44 +0100 Message-ID: <87sebh11i7.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 10.30.177.111 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_H2=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable 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 Peter Krempa writes: > On Tue, Feb 03, 2026 at 13:01:01 +0100, Markus Armbruster wrote: >> Peter Krempa writes: >> >> > From: Peter Krempa >> > >> > Some time ago (commit facda5443f5a8) I've added 'flat' mode (which >> > omits 'backing-image' key in reply) to 'query-named-block-nodes' to >> > minimize the size of the returned JSON for deeper backing chains. >> > >> > While 'query-block' behaved slightly better it turns out that in libvirt >> > we do call 'query-block' to figure out some information about the >> > block device (e.g. throttling info) but we don't look at the backing >> > chain itself. >> > >> > Wire up 'flat' for 'query-block' so that libvirt can ask for an >> > abbreviated output. The implementation is much simpler as the internals >> > are shared with 'query-named-block-nodes'. >> > >> > Signed-off-by: Peter Krempa >> > Acked-by: Markus Armbruster >> >> [...] >> >> > diff --git a/block/qapi.c b/block/qapi.c >> > index 27e0ac6a32..3688d0e713 100644 >> > --- a/block/qapi.c >> > +++ b/block/qapi.c >> >> [...] >> >> > @@ -698,11 +698,12 @@ bdrv_query_bds_stats(BlockDriverState *bs, bool blk_level) >> > return s; >> > } >> > >> > -BlockInfoList *qmp_query_block(Error **errp) >> > +BlockInfoList *qmp_query_block(bool has_flat, bool flat, Error **errp) >> > { >> > BlockInfoList *head = NULL, **p_next = &head; >> > BlockBackend *blk; >> > Error *local_err = NULL; >> > + bool return_flat = has_flat && flat; >> >> This is fine. Just flat would also be fine: flat implies has_flat. Verbose version: This is a QMP command handler. The generated unmarshaler passes has_flat=false, flat=false when @flat is absent, and has_flat=true, flat=F when @flat is present with value F. Therefore, flat can only be true when has_flat is also true. Therefore, flat implies has_flat. Other code calling QMP command handlers (e.g. HMP commands) must satisfy this precondition, too. In fact, any code passing around QAPI-style has_FOO, FOO pairs should stick to the "when has_FOO is false, FOO is zero bits" convention to keep things consistent and predictable. > I've borrowed this from my old patch that added it to > query-named-block-nodes. > > Otherwise I'd have to mark 'has_flat' as unused. Nice side effect would > be that 'flat' can then be used directly in the call to bdrv_query_info. We don't -Wunused-variable, so no need to mark anything. > Alternatively I can move the 'has_flat && flat' expression into the > arguments of the call to bdrv_query_info to avoid the extra local > variable. > > Whichever you prefer. Matter of taste, up to you. I just wanted to make sure you know. >> > >> > GRAPH_RDLOCK_GUARD_MAINLOOP(); >> > >> > @@ -714,7 +715,7 @@ BlockInfoList *qmp_query_block(Error **errp) >> > } >> > >> > info = g_malloc0(sizeof(*info)); >> > - bdrv_query_info(blk, &info->value, &local_err); >> > + bdrv_query_info(blk, return_flat, &info->value, &local_err); >> > if (local_err) { >> > error_propagate(errp, local_err); >> > g_free(info); >> > diff --git a/qapi/block-core.json b/qapi/block-core.json >> > index b82af74256..a701f6bbee 100644 >> > --- a/qapi/block-core.json >> > +++ b/qapi/block-core.json >> > @@ -855,6 +855,10 @@ >> > # >> > # Get a list of `BlockInfo` for all virtual block devices. >> > # >> > +# @flat: Omit nested data about the backing image (ie. the contents at >> > +# 'inserted.image.backing-image' are trimmed). >> > +# Default is false (Since 11.0) >> > +# >> >> s/ie./i.e./ >> >> Remind me: true suppresses member inserted.image.backing-image, i.e. it >> is absent then. Correct? > > Yes the 'backing-image' key is completely missing when @flat is true. Okay. What about this: # @flat: Omit nested data about the backing image, i.e. `BlockInfo` # member 'inserted.image.backing-image' will be absent. Default is # false. (Since 11.0)