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 14C92EB8FAF for ; Wed, 6 Sep 2023 10:47:01 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qdq3R-0007cv-67; Wed, 06 Sep 2023 06:46:37 -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 1qdq3J-0007WN-2T for qemu-devel@nongnu.org; Wed, 06 Sep 2023 06:46:29 -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 1qdq3F-0007L2-Rl for qemu-devel@nongnu.org; Wed, 06 Sep 2023 06:46:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1693997185; 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=0MpFgV4WHywhWdM5SnYO7w2kcF3nd4t5RAnz0sToFrY=; b=fajvy36ZTGiHgQQyXkXdSvMmfZ2fPuVJNMkDsD3pl6epOH6sXW16zP0rIvq5Hn1Z4xVfSz Y84ym9EVw/xsPeW6JmekfU8b0v7oWHpxZhITDL3BfiO3AtlRyGOUZK32VtMWz9McPOYlO4 pJ1g1A7MCybNqMTQYMzS06GYAGAJuhk= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-230-tmGTc_-mOUeEia2eSDF1lA-1; Wed, 06 Sep 2023 06:46:19 -0400 X-MC-Unique: tmGTc_-mOUeEia2eSDF1lA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7A37A805BFB; Wed, 6 Sep 2023 10:46:19 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.47]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4C7DF140E950; Wed, 6 Sep 2023 10:46:18 +0000 (UTC) Date: Wed, 6 Sep 2023 11:46:16 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Cc: Richard Henderson , Peter Xu , qemu-devel@nongnu.org, Juan Quintela , Fabiano Rosas , Thomas Huth , Markus Armbruster Subject: Re: [PATCH v3 4/4] migration/qapi: Drop @MigrationParameter enum Message-ID: References: <20230905162335.235619-1-peterx@redhat.com> <20230905162335.235619-5-peterx@redhat.com> <2edd3a6f-f23d-9a77-db47-4288fe3dbb44@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2edd3a6f-f23d-9a77-db47-4288fe3dbb44@linaro.org> User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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, 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: , 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 Wed, Sep 06, 2023 at 12:14:54PM +0200, Philippe Mathieu-Daudé wrote: > On 6/9/23 11:00, Daniel P. Berrangé wrote: > > On Wed, Sep 06, 2023 at 06:42:16AM +0200, Philippe Mathieu-Daudé wrote: > > > On 5/9/23 18:23, Peter Xu wrote: > > > > Drop the enum in qapi because it is never used in QMP APIs. Instead making > > > > it an internal definition for QEMU so that we can decouple it from QAPI, > > > > and also we can deduplicate the QAPI documentations. > > > > > > > > Reviewed-by: Daniel P. Berrangé > > > > Signed-off-by: Peter Xu > > > > --- > > > > qapi/migration.json | 179 --------------------------------- > > > > migration/options.h | 47 +++++++++ > > > > migration/migration-hmp-cmds.c | 3 +- > > > > migration/options.c | 51 ++++++++++ > > > > 4 files changed, 100 insertions(+), 180 deletions(-) > > > > > > > > > > diff --git a/migration/options.h b/migration/options.h > > > > index 124a5d450f..4591545c62 100644 > > > > --- a/migration/options.h > > > > +++ b/migration/options.h > > > > @@ -66,6 +66,53 @@ bool migrate_cap_set(int cap, bool value, Error **errp); > > > > /* parameters */ > > > > +typedef enum { > > > > + MIGRATION_PARAMETER_ANNOUNCE_INITIAL, > > > > + MIGRATION_PARAMETER_ANNOUNCE_MAX, > > > > + MIGRATION_PARAMETER_ANNOUNCE_ROUNDS, > > > > + MIGRATION_PARAMETER_ANNOUNCE_STEP, > > > > + MIGRATION_PARAMETER_COMPRESS_LEVEL, > > > > + MIGRATION_PARAMETER_COMPRESS_THREADS, > > > > + MIGRATION_PARAMETER_DECOMPRESS_THREADS, > > > > + MIGRATION_PARAMETER_COMPRESS_WAIT_THREAD, > > > > + MIGRATION_PARAMETER_THROTTLE_TRIGGER_THRESHOLD, > > > > + MIGRATION_PARAMETER_CPU_THROTTLE_INITIAL, > > > > + MIGRATION_PARAMETER_CPU_THROTTLE_INCREMENT, > > > > + MIGRATION_PARAMETER_CPU_THROTTLE_TAILSLOW, > > > > + MIGRATION_PARAMETER_TLS_CREDS, > > > > + MIGRATION_PARAMETER_TLS_HOSTNAME, > > > > + MIGRATION_PARAMETER_TLS_AUTHZ, > > > > + MIGRATION_PARAMETER_MAX_BANDWIDTH, > > > > + MIGRATION_PARAMETER_DOWNTIME_LIMIT, > > > > + MIGRATION_PARAMETER_X_CHECKPOINT_DELAY, > > > > + MIGRATION_PARAMETER_BLOCK_INCREMENTAL, > > > > + MIGRATION_PARAMETER_MULTIFD_CHANNELS, > > > > + MIGRATION_PARAMETER_XBZRLE_CACHE_SIZE, > > > > + MIGRATION_PARAMETER_MAX_POSTCOPY_BANDWIDTH, > > > > + MIGRATION_PARAMETER_MAX_CPU_THROTTLE, > > > > + MIGRATION_PARAMETER_MULTIFD_COMPRESSION, > > > > + MIGRATION_PARAMETER_MULTIFD_ZLIB_LEVEL, > > > > + MIGRATION_PARAMETER_MULTIFD_ZSTD_LEVEL, > > > > + MIGRATION_PARAMETER_BLOCK_BITMAP_MAPPING, > > > > + MIGRATION_PARAMETER_X_VCPU_DIRTY_LIMIT_PERIOD, > > > > + MIGRATION_PARAMETER_VCPU_DIRTY_LIMIT, > > > > + MIGRATION_PARAMETER__MAX, > > > > > > MIGRATION_PARAMETER__MAX is not part of the enum, so: > > > > > > #define MIGRATION_PARAMETER__MAX \ > > > (MIGRATION_PARAMETER_VCPU_DIRTY_LIMIT + 1) > > > > IMHO the way it currently is written is better, because the > > __MAX value is guaranteed to always have the right max value > > without needing to be manually changed when new params are > > added. Note this matches the code style used by the QAPI > > enum generator too. > > This concern comes from a previous discussion with Richard (which I > can't find now in the archives) where he explained to me __MAX is not > part of the enum set, thus reduces the coverage of compiler sanitizers > / optimizers, and could introduce subtle bugs. > > This motivated this series: > https://lore.kernel.org/qemu-devel/20230315112811.22355-4-philmd@linaro.org/ > which should have changed that generated QAPI enum. > > (I didn't respin that series because I couldn't find an easy way to > handle conditionals, see > https://lore.kernel.org/qemu-devel/87sfdyaq0m.fsf@pond.sub.org/) Oh, I completely forgot about that series. So the original problem is that with '-Wswitch' present, if the switched variable is an enum type, the compiler complains if you don't list all possible enum values, or have a default: clause. Thus the existance of __MAX forces use to add case ...__MAX, or have a default, and you wanted to eliminate that requirement. Or the surface that sounds reasonable, but I actually think that is the conceptually wrong approach from a robustness POV. C (and some other languages) are terrible wrt enum declared constants vs actual stored values. You can have a variable declared KeyValueKind and it can store absolutely any integer value at all, whether intentionally, or by a code mistake or by data corruption. In your example you modified: switch (key->key->type) { case KEY_VALUE_KIND_NUMBER: qcode = qemu_input_key_number_to_qcode(key->key->u.number.data); name = QKeyCode_str(qcode); trace_input_event_key_number(idx, key->key->u.number.data, name, key->down); break; case KEY_VALUE_KIND_QCODE: name = QKeyCode_str(key->key->u.qcode.data); trace_input_event_key_qcode(idx, name, key->down); break; case KEY_VALUE_KIND__MAX: /* keep gcc happy */ break; } to remove KEY_VALUE_KIND__MAX. What we should actually do IMHO is to either change it to default: g_assert_not_reached(); Or get extra paranoid and -Wswitch-enum too and list both together case KEY_VALUE_KIND__MAX: default: g_assert_not_reached(); This forces us to validate every enum case, and also protect against out of range values. This is a little more verbose to code, but I can't say it has been a maint problem in libvirt where we've followed this approach with -Wswitch-enum and _MAX constants. > Back to this patch, I don't object to having MIGRATION_PARAMETER__MAX > in the enum, but I'd rather have the suggestion below considered. I just prefer to see consistency in approach across the codebase, and currently we use __MAX approach. 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 :|