From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37865) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Wn1nz-0004lp-Dh for qemu-devel@nongnu.org; Wed, 21 May 2014 04:23:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Wn1ns-0007LQ-7N for qemu-devel@nongnu.org; Wed, 21 May 2014 04:23:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:13294) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Wn1nr-0007L6-TQ for qemu-devel@nongnu.org; Wed, 21 May 2014 04:23:12 -0400 Received: from int-mx12.intmail.prod.int.phx2.redhat.com (int-mx12.intmail.prod.int.phx2.redhat.com [10.5.11.25]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s4L8NA5R026796 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Wed, 21 May 2014 04:23:10 -0400 Date: Wed, 21 May 2014 10:23:07 +0200 From: Kevin Wolf Message-ID: <20140521082307.GA3579@noname.redhat.com> References: <1400576881-6954-1-git-send-email-famz@redhat.com> <537BA947.9090800@redhat.com> <20140521015912.GC18886@T430.nay.redhat.com> <87y4xv8ymp.fsf@blackfin.pond.sub.org> <20140521070911.GH18886@T430.nay.redhat.com> <87lhtv60b0.fsf@blackfin.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87lhtv60b0.fsf@blackfin.pond.sub.org> Subject: Re: [Qemu-devel] [RFC PATCH v2 0/7] qapi: Specify default value for optional argument in schema json List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Markus Armbruster Cc: Fam Zheng , qemu-devel@nongnu.org, Stefan Hajnoczi Am 21.05.2014 um 09:46 hat Markus Armbruster geschrieben: > Fam Zheng writes: > > > On Wed, 05/21 07:54, Markus Armbruster wrote: > >> Fam Zheng writes: > >> > >> > On Tue, 05/20 13:13, Eric Blake wrote: > >> >> On 05/20/2014 03:07 AM, Fam Zheng wrote: > >> >> > Please first take a look at patch 7 to see what is supported by this series. > >> >> > > >> >> > Patch 1 ~ 3 allows some useful basic types in schema. > >> >> > > >> >> > Patch 4 ~ 6 implements the new syntax. > >> >> > > >> >> > Note: The introduced '@arg' sigil, just like the preexisting '*arg', is > >> >> > reducing the cleanness of the syntax. We should get rid of both of them in long > >> >> > term. Here, this series compromises on this and introduces '@arg' because: > >> >> > > >> >> > - We have to distinguish the argument property dictionary from nested struct: > >> >> > > >> >> > I.e.: > >> >> > > >> >> > 'data': { > >> >> > 'arg1': { 'member1': 'int', 'member2': 'str' } > >> >> > '@arg2': { 'type': 'int', 'default': 100 } > >> >> > } > >> >> > > >> >> > Until we completely drop and forbid the 'arg1' nested struct use case. > >> >> > > >> >> > - Forbidding 'arg1' it's doable, but doing it now means we pull in many > >> >> > distractive patches to this series. > >> >> > >> >> Question - since we WANT to get rid of nested struct, why not reverse > >> >> the sense? Mark all existing nested structs (weren't there just three > >> >> that we found?) with the '@' sigil, and let the new syntax be > >> >> sigil-free. Then when we clean up the nesting, we are also getting rid > >> >> of the bad syntax, plus the sigil gives us something to search for in > >> >> knowing how much to clean up. But if you stick the sigil on the new > >> >> code, instead of the obsolete code, then as more and more places in the > >> >> schema use defaults, it gets harder and harder to remove the use of the > >> >> sigil even if the nested structs are eventually removed. > >> >> > >> > > >> > It makes not much difference I can see. The hard part is actaully dropping > >> > nested, converting from sigil <-> non-sigil is easy. Of course, nothing is > >> > seriously hard, there are only three nested structs plus some more > >> > qapi-schema > >> > test code. > >> > >> Adding three ugly sigils and making everybody include one when they add > >> a nested struct feels much better to me than ugly sigils all over the > >> place. > > > > Well, I could use some background here. Why did we introduce nested structure > > in the first place? > > Because we could? > > Felt like a good idea at the time? > > I quick glance at commit 0f923be and fb3182c suggests they have been > supported since the beginning. There is no design rationale. Let me extend Fam's question: Why don't we simply remove them right now? If it's really only three instances, converting them to full types should be a matter of five minutes. Kevin