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 48FDAC43458 for ; Mon, 29 Jun 2026 13:03:40 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1weBdu-0001sE-NO; Mon, 29 Jun 2026 09:03:18 -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 1weBdr-0001rp-4c for qemu-devel@nongnu.org; Mon, 29 Jun 2026 09:03:16 -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 1weBdp-0000Gq-QU for qemu-devel@nongnu.org; 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Mon, 29 Jun 2026 13:03:10 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.4]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 502191800661 for ; Mon, 29 Jun 2026 13:03:10 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id CB05021E6920; Mon, 29 Jun 2026 15:03:07 +0200 (CEST) From: Markus Armbruster To: Paolo Bonzini Cc: qemu-devel@nongnu.org Subject: Re: [PATCH v4 0/6] qobject: switch JSON parser to push In-Reply-To: <20260626101727.1727389-1-pbonzini@redhat.com> (Paolo Bonzini's message of "Fri, 26 Jun 2026 12:17:20 +0200") References: <20260626101727.1727389-1-pbonzini@redhat.com> Date: Mon, 29 Jun 2026 15:03:07 +0200 Message-ID: <877bnhts6s.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=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 8 X-Spam_score: 0.8 X-Spam_bar: / X-Spam_report: (0.8 / 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no 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 Paolo Bonzini writes: > This rewrites the json-parser to use a push parser aka state machine. > While push parsers are inherently more complex than recursive descent, > the grammar for JSON is simple enough that the parser remains readable. > There is therefore no need to use e.g. QEMU coroutines. > > Unlike the suggestion in commit 62815d85aed ("json: Redesign the callback > to consume JSON values", 2018-08-24), I kept the json-streamer concept. > It helps in handling input limits, it performs error recovery, and it > converts the token-at-a-time push interface to callbacks---all things > that are more easily done in a separate layer to keep the parser clean. > However, there is no need anymore for it to store partial JSON objects > in tokenized form, because the current state is stored in the push > parser's stack. > > Another benefit is that QEMU can report the first parsing error > immediately, without waiting for parentheses to be balanced or for a > lexing error. Error recovery then proceeds as before (i.e., the next > parse still starts after balanced parentheses or a lexing error). > > On top of the benefits intrinsic in the push architecture, it so happens > that it's really easy to add a location to JSON parsing errors now, so > do that as well. > > The diffstat is unfavorable, but most of the new lines delta is really > new comments explaining the grammar and state machines. I found an unintentional, harmless limit change by one, and suggested a few further comment tweaks. With the limit change reverted or mentioned in the commit message, series Reviewed-by: Markus Armbruster I volunteer to do the pull request, since I have another patch for qobject/ queued up already. I'd apply the changes I suggested, less ones you disagree with. Let me know! [...]