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 EB82BCAC592 for ; Mon, 22 Sep 2025 08:39:35 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1v0c4u-0002E5-Og; Mon, 22 Sep 2025 04:39:21 -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 1v0c4s-0002Ae-8e for qemu-devel@nongnu.org; Mon, 22 Sep 2025 04:39:18 -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 1v0c4j-0005kj-G0 for qemu-devel@nongnu.org; Mon, 22 Sep 2025 04:39:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1758530348; 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=+j//qdN/pDyeeiFh3NPAEpF9l0HZJY+JBpuz6+RrFbc=; b=FancVqb/OI5fW8gPYZRGYc16pFvD07VJ7R1g12e8zdAIp7HoexNOSvUaen27wLZMW42zt0 jyT22Msv04t1XpmFL+cV94OncMNzGDXJ00lsQbvGwJFcjBG/NcKdEhH347OJWYZzyNb6+v CWZ9Rc26CyqhIo+88fUUjiLjZyuEvgQ= 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-232-5Pq2BEtcMteAbapDIiK0xg-1; Mon, 22 Sep 2025 04:39:04 -0400 X-MC-Unique: 5Pq2BEtcMteAbapDIiK0xg-1 X-Mimecast-MFC-AGG-ID: 5Pq2BEtcMteAbapDIiK0xg_1758530343 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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 E82FC195608B; Mon, 22 Sep 2025 08:39:02 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.33]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 087571956056; Mon, 22 Sep 2025 08:39:02 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 4BA5821E6A27; Mon, 22 Sep 2025 10:38:59 +0200 (CEST) From: Markus Armbruster To: "Dr. David Alan Gilbert" Cc: Daniel P. =?utf-8?Q?Berrang=C3=A9?= , qemu-devel@nongnu.org, qemu-block@nongnu.org, Hanna Reitz , Kevin Wolf , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Christian Schoenebeck , Richard Henderson , Manos Pitsidianakis , Stefan Weil , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Gerd Hoffmann , Paolo Bonzini Subject: Re: [PATCH v3 12/20] monitor: introduce monitor_cur_hmp() function In-Reply-To: (David Alan Gilbert's message of "Sat, 20 Sep 2025 11:54:47 +0000") References: <20250910180357.320297-1-berrange@redhat.com> <20250910180357.320297-13-berrange@redhat.com> <87zfaqwr2a.fsf@pond.sub.org> <87ldm9txg0.fsf@pond.sub.org> Date: Mon, 22 Sep 2025 10:38:59 +0200 Message-ID: <87plbinaos.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 3.0 on 10.30.177.17 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: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.442, 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_H5=-1, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=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: 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 "Dr. David Alan Gilbert" writes: > * Markus Armbruster (armbru@redhat.com) wrote: >> Daniel P. Berrang=C3=A9 writes: >>=20 >> > On Fri, Sep 19, 2025 at 02:43:41PM +0200, Markus Armbruster wrote: >> >> Daniel P. Berrang=C3=A9 writes: >> >>=20 >> >> > A number of callers use monitor_cur() followed by !monitor_cur_is_q= mp(). >> >>=20 >> >> "A number of"? I can see just one: >> >>=20 >> >> int error_vprintf(const char *fmt, va_list ap) >> >> { >> >> Monitor *cur_mon =3D monitor_cur(); >> >>=20 >> >> if (cur_mon && !monitor_cur_is_qmp()) { >> >> return monitor_vprintf(cur_mon, fmt, ap); >> >> } >> >> return vfprintf(stderr, fmt, ap); >> >> } >> > >> > Opps, that'll be referring to the other use of monitor_cur() in my >> > patches that I then removed when I re-ordered the series. >> > >> >>=20 >> >> > This is undesirable because monitor_cur_is_qmp() will itself call >> >> > monitor_cur() again, and monitor_cur() must acquire locks and do >> >> > hash table lookups. Introducing a monitor_cur_hmp() helper will >> >> > combine the two operations into one reducing cost. >>=20 >> I think the actual interface flaw is having monitor_cur_is_qmp(). >>=20 >> In master, monitor_cur_is_qmp() is only used in monitor/monitor.c. Both >> call sites have the value of monitor_cur() available as @cur_mon. >> They'd be better off calling monitor_is_qmp(cur_mon). >>=20 >> Note that in master nothing outside monitor/ cares whether a monitor is >> QMP or HMP. I like that. >>=20 >> Your series doesn't preserve this property. >>=20 >> You move the first call site error_vprintf() from monitor/monitor.c to >> util/error-report.c in PATCH 11. QMP vs. HMP is no longer encapsulated. >> Slighly irksome. > > How about a slightly simpler approach, looking above we have: > >> >> if (cur_mon && !monitor_cur_is_qmp()) { >> >> return monitor_vprintf(cur_mon, fmt, ap); >> >> } >> >> return vfprintf(stderr, fmt, ap); > > I think we could replace this with: > > ret =3D monitor_vprintf(cur_mon, fmt, ap); > if (ret =3D=3D -1) { > ret =3D vfprintf(stderr, fmt, ap); > } > return ret; > > monitor_vprintf already -1 exits if !mon or monitor_is_qmp(mon) > > Keeps the encapsulation, and is now 'print via the monitor but if it > can't do it, use printf' monitor_printf() fails when passed a null monitor[*] or a QMP monitor. Reporting the error to stderr then is probably better than swallowing it. Same if the function somehow picks up more failure modes. I like it. One could perhaps object that it makes "report to HMP or else stderr" less obvious if you don't already know that monitor_vprintf() only prints to HMP. I'm okay with that. [*] Feels more like a programming error, but we can ignore this distraction.