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 2FF58C369A2 for ; Tue, 8 Apr 2025 14:38:19 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1u2A4e-0004d6-Ih; Tue, 08 Apr 2025 10:37:12 -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 1u2A4b-0004cS-U8 for qemu-devel@nongnu.org; Tue, 08 Apr 2025 10:37:09 -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 1u2A4a-0002V0-92 for qemu-devel@nongnu.org; Tue, 08 Apr 2025 10:37:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1744123025; 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=h6epCfA2UVDHPBc9HkB+VVA19yy2JMxwvYtGWxttMGY=; b=Ogjq4dv0IyEyxpe8Ge50bDoeFnxIj0ZJCZXbstq9cbRGqfJuOOd+wUh296h1hUcVfLttph u30ekWUeYxQXWO8uSSvsQGaOgx3bzS+v1KDhuJZ65gRPSLl84M0AtpPeVH5O5U5sK9BJoZ XinOhdwjqb37WOEseRr1wUvIx3Lk+ac= Received: from mx-prod-mc-04.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-687-_F8pPfsYPmidoR1JnmdvEw-1; Tue, 08 Apr 2025 10:36:58 -0400 X-MC-Unique: _F8pPfsYPmidoR1JnmdvEw-1 X-Mimecast-MFC-AGG-ID: _F8pPfsYPmidoR1JnmdvEw_1744123017 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (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-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CDF9D1955DCF; Tue, 8 Apr 2025 14:36:56 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.7]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 550361956094; Tue, 8 Apr 2025 14:36:56 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id BC81221E6757; Tue, 08 Apr 2025 16:36:53 +0200 (CEST) From: Markus Armbruster To: Alex =?utf-8?Q?Benn=C3=A9e?= Cc: Mario Fleischmann , qemu-devel@nongnu.org, philmd@linaro.org, christian.boenig@lauterbach.com Subject: Re: [PATCH 00/16] Add Multi-Core Debug (MCD) API support In-Reply-To: <87y0wahh65.fsf@draig.linaro.org> ("Alex =?utf-8?Q?Benn=C3=A9?= =?utf-8?Q?e=22's?= message of "Tue, 08 Apr 2025 15:16:50 +0100") References: <20250310150510.200607-1-mario.fleischmann@lauterbach.com> <87semkw3qx.fsf@pond.sub.org> <87semjp286.fsf@pond.sub.org> <0736943f-443b-4bfc-8d69-f30f42029d07@lauterbach.com> <87r023m422.fsf@pond.sub.org> <87a58qj3ay.fsf@draig.linaro.org> <87ldsakgp9.fsf@pond.sub.org> <87y0wahh65.fsf@draig.linaro.org> Date: Tue, 08 Apr 2025 16:36:53 +0200 Message-ID: <87mscqiut6.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 10.30.177.15 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: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.845, 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_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=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 Alex Benn=C3=A9e writes: > Markus Armbruster writes: > >> Alex Benn=C3=A9e writes: >> >>> Markus Armbruster writes: >>> >>>> Mario Fleischmann writes: >>>> >>>>> Apologies for the line wrapping in yesterday's answer. Should be fixe= d now. >>>>> >>>>> On 08.04.2025 09:00, Markus Armbruster wrote: >> >> [...] >> >>>>>> What about providing the MCD interface as a separate QMP-like protoc= ol? >>>>>> It gets its own QAPI schema, just like for qemu-ga. Simplifies >>>>>> compiling it out when not needed. >>>>>> >>>>>> It gets its own socket, just like the GDB stub. Might reduce >>>>>> interference between debugging and QMP. >>>>>>=20 >>>>>> Thoughts? Alex, Philippe, care to chime in? >>>>> >>>>> Sound reasonable to me. Keeping in mind the size of generated QAPI co= de, >>>>> an option to `./configure [...] --enable-mcd` is definitely advisable. >>>> >>>> Alex, Philippe? >>> >>> When I spoke to Mario at DVCon last year I liked the idea of re-using >>> QMP instead of inventing yet another RPC interface for QEMU. QMP >>> certainly has nicer properties than the gdbstub which has a very >>> "organic" and "serial" feel to it. >>> >>> Are you suggesting we re-use the machinery but use an entirely separate >>> socket with just the MCD namespace in it? I don't see that being a >>> problem as long as we can test it properly in the CI. >> >> Yes. >> >> "Keep them separate" is only a gut feeling, though. While I pay >> attention to my gut feelings, I know they can be wrong. I am soliciting >> opinions. > > I forgot to add isn't the flexibility of the QMP API something we need > to handle for single binary anyway? I have no idea :) Evolving a target-dependent interface into a target-independent interface without breaking compatibility is always a bother. It's likely more of a bother when the interface is binary. Textual interfaces tend to have less target-dependence. Designing a target-independent interface is probably easier than evolving it compatibly from a target-dependent one. QMP is textual, and it's designed for certain kinds of compatible evolution. Using QAPI/QMP for a debugging interface may be a perfectly sensible idea. I don't know enough about debugging interfaces to judge. Use of QAPI/QMP does not imply use of the QMP monitor. We can keep the monitor and the debugging interface separate even though both are based on QAPI/QMP. The monitor code is gnarly, I'm afraid. It supports multiple monitors, but they are not fully independent for historical reasons, chiefly implied mutual exclusion for commands. Adding a QAPI/QMP-based debugging interface without undue coupling to monitors may pose a few technical problems. One way to find out.