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Mon, 23 Aug 2021 15:27:21 +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> Date: Mon, 23 Aug 2021 15:27:21 +0200 In-Reply-To: (Jonah Palmer's message of "Tue, 10 Aug 2021 02:36:43 -0400") Message-ID: <87v93wcmva.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 10.5.11.14 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=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.743, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-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: 2.1.23 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" Back from my summer break, please excuse the delay. Jonah Palmer writes: > On 8/7/21 8:35 AM, Markus Armbruster wrote: >> QAPI schema review only. >> >> Jonah Palmer writes: >> >>> From: Laurent Vivier >>> >>> This new command lists all the instances of VirtIODevice with >>> their path and virtio type. >>> >>> Signed-off-by: Laurent Vivier >>> Reviewed-by: Eric Blake >>> Signed-off-by: Jonah Palmer >> [...] >> >>> diff --git a/qapi/qapi-schema.json b/qapi/qapi-schema.json >>> index 4912b97..0c89789 100644 >>> --- a/qapi/qapi-schema.json >>> +++ b/qapi/qapi-schema.json >>> @@ -91,5 +91,6 @@ >>> { 'include': 'misc.json' } >>> { 'include': 'misc-target.json' } >>> { 'include': 'audio.json' } >>> +{ 'include': 'virtio.json' } >>> { 'include': 'acpi.json' } >>> { 'include': 'pci.json' } >>> diff --git a/qapi/virtio.json b/qapi/virtio.json >>> new file mode 100644 >>> index 0000000..804adbe >>> --- /dev/null >>> +++ b/qapi/virtio.json >>> @@ -0,0 +1,72 @@ >> Please insert at the beginning >> >> # -*- Mode: Python -*- >> # vim: filetype=python >> # > > Will do. > >>> +## >>> +# = Virtio devices >>> +## >>> + >>> +## >>> +# @VirtioType: >>> +# >>> +# An enumeration of Virtio device types. >>> +# >>> +# Since: 6.1 >> 6.2 now, here and below. > > Okay, will update for entire series. > >> >>> +## >>> +{ 'enum': 'VirtioType', >>> + 'data': [ 'unknown', 'virtio-net', 'virtio-blk', 'virtio-console', >>> + 'virtio-rng', 'virtio-balloon', 'virtio-iomem', 'virtio-rpmsg', >>> + 'virtio-scsi', 'virtio-9p', 'virtio-mac80211-wlan', >>> + 'virtio-serial', 'virtio-caif', 'virtio-memory-balloon', >>> + 'unknown-14', 'unknown-15', 'virtio-gpu', 'virtio-clock', >>> + 'virtio-input', 'vhost-vsock', 'virtio-crypto', 'virtio-signal-dist', >>> + 'virtio-pstore', 'virtio-iommu', 'virtio-mem', 'unknown-25', >>> + 'vhost-user-fs', 'virtio-pmem', 'unknown-28', 'virtio-mac80211-hwsim' ] >> Please limit line length to approximately 70 characters. > > Fixed, sorry about that. Also, should I continue this up to 'virtio-bluetooth'? E.g: > > ... > 'virtio-mac80211-hwsim', 'unknown-30', 'unknown-31', > 'unknown-32', 'unknown-33', 'unknown-34', 'unknown-35', > 'unknown-36', 'unknown-37', 'unknown-38', 'unknown-39', > 'virtio-bluetooth' ] 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. 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", ... } 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. [...]