From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51776) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1d6H29-0001Vc-SD for qemu-devel@nongnu.org; Thu, 04 May 2017 09:43:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1d6H26-0001Xh-Pp for qemu-devel@nongnu.org; Thu, 04 May 2017 09:43:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36938) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1d6H26-0001Xd-Fu for qemu-devel@nongnu.org; Thu, 04 May 2017 09:43:02 -0400 From: Markus Armbruster References: <20170502203115.22233-1-ehabkost@redhat.com> <20170502203115.22233-3-ehabkost@redhat.com> <87y3udsz3k.fsf@dusky.pond.sub.org> <20170503183037.GV3482@thinpad.lan.raisama.net> <87vaphm4fs.fsf@dusky.pond.sub.org> <0778f9a5-d974-9beb-ae94-b8e46de7b75d@redhat.com> Date: Thu, 04 May 2017 15:42:59 +0200 In-Reply-To: <0778f9a5-d974-9beb-ae94-b8e46de7b75d@redhat.com> (Eric Blake's message of "Thu, 4 May 2017 08:23:33 -0500") Message-ID: <871ss4d9gc.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH 2/4] string-input-visitor: Support alternate types List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake Cc: Eduardo Habkost , Alexander Graf , qemu-devel@nongnu.org, Michael Roth , Igor Mammedov , Paolo Bonzini , Richard Henderson Eric Blake writes: > On 05/04/2017 03:06 AM, Markus Armbruster wrote: >> Eduardo Habkost writes: >> >>> On Wed, May 03, 2017 at 06:07:43PM +0200, Markus Armbruster wrote: >>>> Eduardo Habkost writes: >>>> >>>>> When parsing alternates from a string, there are some limitations in >>>>> what we can do, but it is a valid use case in some situations. We can >>>>> support booleans, integer types, and enums. >> >> By the way, the same restrictions apply to the "keyval" variant of the >> QObject input visitor. It's a known problem stated here: >> >> Message-ID: <8737exuz6u.fsf@dusky.pond.sub.org> >> https://lists.gnu.org/archive/html/qemu-devel/2017-03/msg00046.html >> >> However, I failed to document it properly in the source. >> > >>>> Begs the question what happens when you violate these restrictions. >>> >>> Right now, we don't detect those cases and behavior is undefined. >>> I think it will be a good idea to give start_alternate() enough >>> information to detect those cases (by adding a 'const char *const >>> enum_table[]' parameter). >> >> Alternate types that won't work with the string input visitor can be >> detected at compile time (by qapi.py), but not their actual use. Pity. >> >> Do we actually use alternates that violate the restrictions? If not, we >> could simply restrict alternates so they work with *all* visitors. If >> we ever run into an actual need for alternates that don't, we'll be no >> worse off than now. >> >> Let's review existing alternates outside tests: >> >> * Qcow2OverlapChecks: struct + enum >> * BlockdevRef: struct + str >> * GuestFileWhence: int + enum (all enum members start with a letter) >> >> Restricting alternates looks practical to me. Eric, what do you think? > > As in: we forbid the combination of a scalar (whether 'int', 'number', > 'bool', and perhaps 'null') with a plain 'str' (since there's no way to > tell whether '1' should parse as an integer or the string "1"); and > combining a scalar with an 'enum' requires that all enum members be > distinct from what could otherwise be parsed as a scalar? Exactly. > I can live > with such a restriction. Then let's do it. Eduardo, are you comfortable implementing this, or would you like me to do it?