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Wed, 21 Oct 2020 06:19:51 +0200 (CEST) From: Markus Armbruster To: Eric Blake Subject: Re: [PATCH v4 4/7] nbd: Update qapi to support exporting multiple bitmaps References: <20201009215533.1194742-1-eblake@redhat.com> <20201009215533.1194742-5-eblake@redhat.com> <6ee3ac4f-65c3-fdfd-9adb-9bea5f5739e3@virtuozzo.com> <56b413b5-2213-1b4e-5cac-865d8f0e0689@redhat.com> <87lfg1gu06.fsf@dusky.pond.sub.org> <4d7d4c9b-3b32-0c13-9ec1-b326e49ca7ae@redhat.com> Date: Wed, 21 Oct 2020 06:19:51 +0200 In-Reply-To: <4d7d4c9b-3b32-0c13-9ec1-b326e49ca7ae@redhat.com> (Eric Blake's message of "Tue, 20 Oct 2020 13:26:19 -0500") Message-ID: <87v9f48b2w.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (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=63.128.21.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/20 22:12:28 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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_H5=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org, qemu-devel@nongnu.org, rjones@redhat.com, stefanha@redhat.com, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eric Blake writes: > On 10/20/20 3:51 AM, Markus Armbruster wrote: > >>> #define QAPI_LIST_ADD(list, element) do { \ >>> typeof(list) _tmp = g_new(typeof(*(list)), 1); \ >>> _tmp->value = (element); \ >>> _tmp->next = (list); \ >>> (list) = _tmp; \ >>> } while (0) >>> >>> >>> Markus, thoughts on if we should publish this macro, >> >> If it's widely useful. >> >> "git-grep -- '->value ='" matches ~200 times. A patch converting these >> to the macro where possible would make a strong case for having the >> macro. >> >>> and if so, which >>> header would be best? >> >> The macro is generic: @list's type may be any of the struct TYPEList we >> generate for the QAPI type ['TYPE']. >> >> We don't want to generate this macro next to each of these struct >> definitions. A non-generic macro would go there, but let's not generate >> almost a hundred non-generic macros where a single generic one can do >> the job. > > Agreed. > >> >> The closest we have to a common base is GenericList. It's in in >> visitor.h because it's only used by visitors so far. Adding the macro >> next it is not so smart, because we don't want non-visitor code to >> include visitor.h just for this macro. > > Also agreed. > >> >> Perhaps the macro should go into qapi/util.h, and perhaps GenericList >> and GenericAlternate should move there, too. > > GenericList is easy, but GenericAlternate is harder: it would introduce > a cyclic declaration dependency (generated qapi-builtin-types.h includes > qapi/util.h for the definition of QEnumLookup, but qapi/util.h declaring > GenericAlternate would depend on including qapi-builtin-types.h for the > definition of QType). You're right. QType is a built-in QAPI type. The typedef is generated into qapi-builtin-types.h. It needs to be a QAPI type because it's the type of alternates' (implicit) member @type. I figure the easiest way to move GenericAlternate (if we want to), is creating a new header, or rather splitting qapi/util.h into the part needed by qapi-builtin-types.h and the part that needs qapi-builtin-types.h. Doesn't seem to be worth our while now. We can simply put the macro into qapi/util.h and call it a day.