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Iglesias" , Jason Wang , Marcelo Tosatti , kvm@vger.kernel.org, Alberto Garcia , Kevin Wolf , Hanna Reitz , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Zhao Liu , Jonathan Cameron , Junjie Cao , Anisa Su , Elena Ufimtseva , Jagannathan Raman , John Levon , Thanos Makatos , =?utf-8?Q?C=C3=A9dric?= Le Goater , Cornelia Huck , Eric Farman , Matthew Rosato , Richard Henderson , Ilya Leoshkevich , qemu-block@nongnu.org, linux-cxl@vger.kernel.org, qemu-s390x@nongnu.org, "Michael S. Tsirkin" , Sergio Lopez , qemu-arm@nongnu.org, Palmer Dabbelt , Alistair Francis , Weiwei Li , Daniel Henrique Barboza , Liu Zhiwei , Chao Liu , qemu-riscv@nongnu.org, Song Gao <17746591750@163.com>, Bibo Mao , Xianglai Li , Jiaxun Yang , Pedro Barbuda , Mohamed Mediouni , Nicholas Piggin , Harsh Prateek Bora , Amit Machhiwal , qemu-ppc@nongnu.org, Zhang Chen , Li Zhijian , Alistair Francis , Alexander Graf , "Gonglei (Arei)" , zhenwei pi , Ani Sinha , Luc Michel , =?utf-8?Q?C=C3=A9dric?= Le Goater , Jamin Lin , Kane Chen , Samuel Tardieu , "Denis V. Lunev" , FangSheng Huang , Tyrone Ting , Hao Wu , Keith Busch , Klaus Jensen , Jesper Devantier , Aditya Gupta , Glenn Miles , Conor Dooley , Sebastian Huber , Halil Pasic , Christian Borntraeger , Jason Herne , Titus Rwantare , Stefano Stabellini , Anthony PERARD , Peter Xu , Chinmay Rath , Hendrik Brueckner , xen-devel@lists.xenproject.org, Roman Bolshakov , Phil Dennis-Jordan , Fam Zheng , Farhan Ali , Alex Williamson , Tao Tang , Stefan Berger , Fabiano Rosas , Mark Cave-Ayland , Artyom Tarasenko , Yoshinori Sato , Jiri Pirko , Eric Auger , Laurent Vivier Subject: Re: [PATCH v7 54/65] qdev: adjust PciDevfn declared type Message-ID: Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20261020-qom-qapi-v7-0-431a86b02b58@redhat.com> <20261020-qom-qapi-v7-54-431a86b02b58@redhat.com> <87zevz5h4k.fsf@pond.sub.org> X-Mailing-List: kvm@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87zevz5h4k.fsf@pond.sub.org> User-Agent: Mutt/2.4.2 (2026-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On Tue, Oct 27, 2026 at 03:54:03PM +0100, Markus Armbruster wrote: > Marc-André Lureau writes: > > > Hi > > > > On Fri, Oct 23, 2026 at 2:04 PM Daniel P. Berrangé wrote: > >> > >> On Tue, Oct 20, 2026 at 02:46:11PM +0400, Marc-André Lureau wrote: > >> > PciDevfn is a bit special, since it accepts integer and string as > >> > setter, but only output integer as getter. snip > > But I agree we > > could do better. > > > > There are multiple options. We could keep declaring the property as > > str instead. In this case, the getter should probably return a string > > for consistency and correctness. This might surprise some existing > > users though. > > I.e. ditch numeric suppport for numeric addresses, right? > > Incompatible change. Do we care? > > If we don't, we should be honest about it and mark qom-get unstable. > > > We could introduce new properties like `devfn-str` and `devfn-int` > > that alias the same value. > > Compatibility break. If breaking compatibility is okay, I'd rather use > the opportunity to get rid of cleverness, and go with your first option. > > > We could also introduce a new structured QAPI type. > > What kind of type do you have in mind? IMHO the root cause design flaw here was to overload 'addr' as a way to set both the slot number and function number, as using one property for two pieces of data is a well known anti-pattern we caution against. IOW, we should have had 'slot' and 'function' as separate properties from the start. >From a CLI POV, we could easily change 'addr' to mean only the slot number, since it is always parsed in string format without the magic (slot << 4) | function encoding. Then add a 'function' prop The challenge is the impact on QMP with strict typing, as ideally int format would soley represent the slot number, but today the int format is encoded (slot << 4) | function. So anyone relying on int format in QMP would silently have a semantic change if we altered what 'addr' means. Deprecating 'addr' entirely and adding brand new 'slot' and 'function' properties would be a significant disruption to a syntax which has been documented for years (decades). With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|