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 2A5E0CAC5AE for ; Wed, 24 Sep 2025 16:11:40 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1v1S4f-0001zB-LW; Wed, 24 Sep 2025 12:10:33 -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 1v1S4c-0001yH-J3 for qemu-devel@nongnu.org; Wed, 24 Sep 2025 12:10:30 -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 1v1S4U-0004cv-WD for qemu-devel@nongnu.org; Wed, 24 Sep 2025 12:10:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1758730219; h=from:from:reply-to: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=AqnhL2B36mwyvI3Hblfzg1Xi+lOXoyJq5C151SoWKFE=; b=IJMhSZSmXRGRNZO0XmrI0AfYMsK1fk7Ve3AQO8D/+YSqkqRMsc1e9Jjo/45oR0Aqb+3N4u /0IYJIDwhvlufH9vQdLvFHw/FEOqE4LC6PXQSxCqKLlKIrVTPEigroz2QxigP96MTzzoH6 wDJQyxJNNVu2zOQaqFhJrDGIT0kCcK0= 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-338-bQ5eBMNDNhiGGUR2ozDybg-1; Wed, 24 Sep 2025 12:10:17 -0400 X-MC-Unique: bQ5eBMNDNhiGGUR2ozDybg-1 X-Mimecast-MFC-AGG-ID: bQ5eBMNDNhiGGUR2ozDybg_1758730214 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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1913A195608B; Wed, 24 Sep 2025 16:10:14 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.136]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B7E28180057C; Wed, 24 Sep 2025 16:10:00 +0000 (UTC) Date: Wed, 24 Sep 2025 17:09:53 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Cc: "Dr. David Alan Gilbert" , 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 Message-ID: References: <20250910180357.320297-1-berrange@redhat.com> <20250910180357.320297-13-berrange@redhat.com> <87zfaqwr2a.fsf@pond.sub.org> <87ldm9txg0.fsf@pond.sub.org> <87plbinaos.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87plbinaos.fsf@pond.sub.org> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@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=-0.444, 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=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_PASS=-0.001, T_SPF_HELO_TEMPERROR=0.01 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Sep 22, 2025 at 10:38:59AM +0200, Markus Armbruster wrote: > "Dr. David Alan Gilbert" writes: > > > * Markus Armbruster (armbru@redhat.com) wrote: > >> Daniel P. Berrangé writes: > >> > >> > On Fri, Sep 19, 2025 at 02:43:41PM +0200, Markus Armbruster wrote: > >> >> Daniel P. Berrangé writes: > >> >> > >> >> > A number of callers use monitor_cur() followed by !monitor_cur_is_qmp(). > >> >> > >> >> "A number of"? I can see just one: > >> >> > >> >> int error_vprintf(const char *fmt, va_list ap) > >> >> { > >> >> Monitor *cur_mon = monitor_cur(); > >> >> > >> >> 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. > >> > > >> >> > >> >> > 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. > >> > >> I think the actual interface flaw is having monitor_cur_is_qmp(). > >> > >> 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). > >> > >> Note that in master nothing outside monitor/ cares whether a monitor is > >> QMP or HMP. I like that. > >> > >> Your series doesn't preserve this property. > >> > >> 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 = monitor_vprintf(cur_mon, fmt, ap); > > if (ret == -1) { > > ret = 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. I've tried this and it works nicely and helps me with some other aspects too. > 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. 'error_vprintf()' itself is already non-obvious, as you'd never guess it implied any interaction with the monitor at all :-) A little comment clarifies things sufficiently well. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|