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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E6528C433E0 for ; Mon, 22 Jun 2020 08:06:12 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id AF6A020707 for ; Mon, 22 Jun 2020 08:06:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gYGSV0XB" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AF6A020707 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:41118 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jnHT2-0008Im-0m for qemu-devel@archiver.kernel.org; Mon, 22 Jun 2020 04:06:12 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57656) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jnHSG-0007kT-J9 for qemu-devel@nongnu.org; Mon, 22 Jun 2020 04:05:24 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:41200 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jnHSD-0005Ps-TI for qemu-devel@nongnu.org; Mon, 22 Jun 2020 04:05:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1592813120; 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=qMfk74iK4l6u2z9/YpvJYuNaWVJBuzEVNrXDQoO8/bA=; b=gYGSV0XBl7SzSf7B+ntLAjOERfGlQIcgiUB6NdI6MAOh3Ymx+T9Nxi7GkezUILdBQvrNhM Na4TOMAOH86Fatuqismrhn/6HsLjXj8IRybzx+QgLNVWGwLTsuH0besSjR0x93gStJyFUL FAN61FI4b9WTlwD6ejLXzWNwcl9ReOU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-237-Yn4KbcINOPSgHygpxLGHBQ-1; Mon, 22 Jun 2020 04:05:16 -0400 X-MC-Unique: Yn4KbcINOPSgHygpxLGHBQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EE981835B40 for ; Mon, 22 Jun 2020 08:05:15 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-121.ams2.redhat.com [10.36.112.121]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3B22B6FDD1; Mon, 22 Jun 2020 08:05:13 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id AFE15113846D; Mon, 22 Jun 2020 10:05:11 +0200 (CEST) From: Markus Armbruster To: David Hildenbrand Subject: Re: [PATCH v2] hmp: Make json format optional for qom-set References: <20200610075153.33892-1-david@redhat.com> <87pna0c0pr.fsf@dusky.pond.sub.org> <70d42699-f17b-320e-3a21-4454978ca8d6@redhat.com> Date: Mon, 22 Jun 2020 10:05:11 +0200 In-Reply-To: <70d42699-f17b-320e-3a21-4454978ca8d6@redhat.com> (David Hildenbrand's message of "Mon, 15 Jun 2020 09:45:52 +0200") Message-ID: <87d05rr0eg.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=207.211.31.120; envelope-from=armbru@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/22 02:57:26 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Daniel P. =?utf-8?Q?Berrang=C3=A9?=" , Eduardo Habkost , "Dr . David Alan Gilbert" , qemu-devel@nongnu.org, Paolo Bonzini , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" David Hildenbrand writes: > On 15.06.20 08:17, Markus Armbruster wrote: >> David Hildenbrand writes: >> >>> Commit 7d2ef6dcc1cf ("hmp: Simplify qom-set") switched to the json >>> parser, making it possible to specify complex types. However, with this >>> change it is no longer possible to specify proper sizes (e.g., 2G, 128M), >>> turning the interface harder to use for properties that consume sizes. >>> >>> Let's switch back to the previous handling and allow to specify passing >>> json via the "-j" parameter. >> >> Two issues: >> >> 1. Makes qom-get and qom-set inconsistent >> >> qom-get formats as JSON, always. >> >> qom-set parses the string visitor's undocumented ad hoc language by >> default. You can make it parse JSON by passing -j. > > This is the same language the QEMU cmdline uses, no? The CLI uses many, many languages. The string visitor's language may well be among them; can't tell offhand. > >> >> Not a show stopper, but sure ugly. I feel documentation should point >> it out. > > Sure, we can fine-tune the documentation. For now we didn't have any > qom-get users, in contrast to qom-set. Not sure if it makes sense to > implement the same functionality for qom-get. > > For now I can e.g., > > "echo "qom-set vm1 requested-size 256M" | sudo nc -U /var/tmp/mon_src" > > then I can > > echo "qom-get vm1 requested-size " | sudo nc -U /var/tmp/mon_src > -> 268435456 > > which is a value I can punch back into qom-set. At least for sizes this > works. Not perfect, not bad. Opinions? It happens to work in this case, because the JSON number returned by qom-get happens to get parsed the right way by qom-set. Is this the case for all properties where qom-set isn't deadly due to issue 2.? Nobody knows. >> 2. Rearms the string visitor death trap >> >> If you try to qom-set a property whose ->set() uses something the >> string input visitor doesn't support, QEMU crashes. I'm not aware of >> such a ->set(), but this is a death trap all the same. Mind, I >> didn't actually *look* for such a ->set(). Details: > > Thanks. Maybe I am missing something important, but this sounds like we > are missing a bunch of checks+errors. The string visitor feels like a quick hack to get something that is human-friendly. It provides just enough functionality for its initial uses. The trouble is new uses that violate its restrictions are hard to spot. In my opinion, what we're really missing a replacement of the ill-conceived string visitor. The less it's used, the better. Since a replacement isn't being worked on, we may have to make it less dangerous to use. Patches welcome. > (wouldn't we be able to crash > using the QEMU cmdline as well when setting such properties?). If the string visitor is used there. Nobody knows. >> Subject: Re: [RFC PATCH] qom: Implement qom-get HMP command >> Date: Sat, 02 May 2020 08:02:43 +0200 (6 weeks, 2 days, 4 minutes ago) >> Message-ID: <87a72q6fi4.fsf@dusky.pond.sub.org> >> https://lists.nongnu.org/archive/html/qemu-devel/2020-05/msg00178.html >> >> Since we've had this death trap in the code for a number of years, I >> can't call its restoration a show stopper. It does feel like an >> unadvisable risk, though. >> > > As long as there are no better alternatives to punch in data in the same > format the QEMU cmdline consumes, I think this is perfectly reasonable. > No good reason to make a HMP interface harder to use by humans IMHO. Yes, HMP should be human-friendly. Not at any cost, though; I reiterate my conviction that this is an unadvisable risk. A crash is the most unfriendly response of all.