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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 15F66C433F5 for ; Fri, 3 Sep 2021 13:23:13 +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 A127360FDC for ; Fri, 3 Sep 2021 13:23:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org A127360FDC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:36888 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mM99z-0000e9-Ml for qemu-devel@archiver.kernel.org; Fri, 03 Sep 2021 09:23:11 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47644) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mM8wM-0008NP-7E for qemu-devel@nongnu.org; Fri, 03 Sep 2021 09:09:06 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:52370) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mM8wK-0001aR-FE for qemu-devel@nongnu.org; Fri, 03 Sep 2021 09:09:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1630674543; 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=V+gx2ZV37n0r1wjvtRnl1zOB0aJr01rmmUAK0ovYuaU=; b=NnAKe8vQ3Am5035MYcDRNI4HYc3jcwcUnz1uBsZnt6CcscbWFTS2p2rq9rRbP+TMYElYz+ uSM9IilqGCzOHZEpVfHapOrGD6bC/ZcROqba3hkQdAAaHwPyQhICnQK9IdalexFHm9+CHJ TDAlfAMAhvSHTFsPD1TqlNyYbo2HoLs= 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-21-OinkoYl7Ot28fCsVTQLqkw-1; Fri, 03 Sep 2021 09:09:02 -0400 X-MC-Unique: OinkoYl7Ot28fCsVTQLqkw-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 13C06107ACC7; Fri, 3 Sep 2021 13:09:01 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-13.ams2.redhat.com [10.36.112.13]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9966A6608B; Fri, 3 Sep 2021 13:08:33 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 4D5BA11385C7; Wed, 1 Sep 2021 13:15:55 +0200 (CEST) From: Markus Armbruster To: Jonah Palmer Subject: Re: [PATCH v6 1/6] qmp: add QMP command x-debug-query-virtio References: <1626086137-16292-1-git-send-email-jonah.palmer@oracle.com> <1626086137-16292-2-git-send-email-jonah.palmer@oracle.com> <87o8a9e8k8.fsf@dusky.pond.sub.org> <87v93wcmva.fsf@dusky.pond.sub.org> <0298fc69-d7f7-ae7a-eb1d-ee553aaf8348@oracle.com> Date: Wed, 01 Sep 2021 13:15:55 +0200 In-Reply-To: <0298fc69-d7f7-ae7a-eb1d-ee553aaf8348@oracle.com> (Jonah Palmer's message of "Thu, 26 Aug 2021 02:18:07 -0400") Message-ID: <87o89cbl78.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain 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: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.392, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: fam@euphon.net, mst@redhat.com, jasowang@redhat.com, qemu-devel@nongnu.org, kraxel@redhat.com, si-wei.liu@oracle.com, joao.m.martins@oracle.com, qemu-block@nongnu.org, david@redhat.com, marcandre.lureau@redhat.com, thuth@redhat.com, amit@kernel.org, michael.roth@amd.com, dgilbert@redhat.com, eric.auger@redhat.com, dmitrii.stepanov@cloud.ionos.com, stefanha@redhat.com, Boris Ostrovsky , kwolf@redhat.com, laurent@vivier.eu, mreitz@redhat.com, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Jonah Palmer writes: > No problem! Comments below: > > On 8/23/21 9:27 AM, Markus Armbruster wrote: [...] >> Hmm... how is this enum used? In this patch: >> >> VirtioInfoList *qmp_x_debug_query_virtio(Error **errp) >> { >> VirtioInfoList *list = NULL; >> VirtioInfoList *node; >> VirtIODevice *vdev; >> >> QTAILQ_FOREACH(vdev, &virtio_list, next) { >> DeviceState *dev = DEVICE(vdev); >> node = g_new0(VirtioInfoList, 1); >> node->value = g_new(VirtioInfo, 1); >> node->value->path = g_strdup(dev->canonical_path); >> ---> node->value->type = qapi_enum_parse(&VirtioType_lookup, vdev->name, >> ---> VIRTIO_TYPE_UNKNOWN, NULL); >> QAPI_LIST_PREPEND(list, node->value); >> } >> >> return list; >> } >> >> This maps VirtioDevice member @name (a string) to an enum value. >> >> As far as I can tell, this member is set in virtio_init() only, to its >> argument. All callers pass string literals. They also pass a numeric >> device_id, and the two seem to match, e.g. "virtio-blk" and >> VIRTIO_ID_BLOCK. >> >> Thus, the pairs (numeric device ID, string device ID) already exist in >> the code, but not in a way that lets you map between them. To get that, >> you *duplicate* the pairs in QAPI. >> >> Having two copies means we get to keep them consistent. Can we avoid >> that? >> >> The enum has a special member 'unknown' that gets used when @name does >> not parse as enum member, i.e. we failed at keeping the copies >> consistent. I'm afraid this sweeps a programming error under the rug. >> >> The enum has a bunch of dummy members like 'unknown-14' to make QAPI >> generate numeric enum values match the device IDs. Error prone. Can't >> see offhand why we need them to match. > > Sure, I don't mind doing this instead. Just as an FYI, from the previous > RFC series (RFC v5 1/6), David recommended here that I create a list of > all the types and in the same order as include/standard-headers/linux/virtio_ids.h. > > The benefit from this was that we never have to convert between the QAPI number > and the header number. Yes, but it comes with the disadvantages I listed above. > Let me know if this is still something you'd like me to do! I think it's simpler overall, especially if you can pick option "2. Without QAPI enum VirtioType" below. I could be wrong. Suggest to try it out to see what you like better. >> >> What about the following. Define a map from numeric device ID to >> string, like so >> >> const char *virtio_device_name[] = { >> [VIRTIO_ID_NET] = "virtio-net", >> [VIRTIO_ID_BLOCK] = "virtio-blk", >> ... >> } > > Sorry if this is obvious, but where should I define this mapping? > virtio.c or virtio.h? Variable definitions normally live in .c. > Jonah > >> This lets you >> >> * map device ID to string by subscripting virtio_device_name[]. >> Guarding with assert(device_id < G_N_ELEMENTS(virtio_device_name)) may >> be advisable. >> >> * map string to device ID by searching virtio_device_name[]. May want a >> function for that, >> >> Now you can have virtio_init() map parameter @device_id to string, and >> drop parameter @name. >> >> Then you have two options: >> >> 1. With QAPI enum VirtioType >> >> Define it without the special and the dummy members. >> >> To map from string to QAPI enum, use qapi_enum_parse(). >> >> To map from QAPI enum to string, use VirtioType_str(). >> >> To map from QAPI enum to device ID, map through string. >> >> 2. Without QAPI enum VirtioType >> >> Simply use uint16_t device_id, just like struct VirtioDevice. >> >> The choice between 1. and 2. depends on whether you actually need >> additional functionality provided by QAPI, such as types being visible >> in query-qmp-schema. >> >> [...] >>