[Quoted material edited somewhat to provide better context] Paolo Bonzini <pbonz...@redhat.com> writes:
> Il 02/10/2014 16:59, Markus Armbruster ha scritto: >> Andreas Färber <afaer...@suse.de> writes: >> >>> Am 02.10.2014 um 16:21 schrieb Markus Armbruster: >>>> Andreas Färber <afaer...@suse.de> writes: >>>> >>>>> Am 02.10.2014 um 15:21 schrieb Stefan Hajnoczi: >>>>>> On Wed, Oct 01, 2014 at 02:33:47PM +0200, Markus Armbruster wrote: >>>>>>> Markus Armbruster <arm...@redhat.com> writes: >>>>>>> >>>>>>> Actually, "property names are arbitrary strings" has recently become >>>>>>> untrue: commit 339659 "qom: Add automatic arrayification to >>>>>>> object_property_add()" changed names to have embedded syntax. A >>>>>>> property name ending with "[*]" makes the property special. Normal >>>>>>> properties can be added just once, and an attempt to add it again is an >>>>>>> error. These special properties, however, can be added any number of >>>>>>> times, and each time the name "[*]" is silently rewritten to "[N]", >>>>>>> where N counts from 0. [...] >>>>>>> Is mangling array-ness into the name really a good idea? Isn't this >>>>>>> type matter, not name matter? >>>>>> >>>>>> I agree. It's nasty to hack the array selector into the name and will >>>>>> probably cause us pain down the line. >>>> >>>> Andreas? >>> >>> -> Paolo ;) >> >> Paolo? > > Uhm, I had written an answer but Thunderbird ate it. Oh well. > > I think foo[*] is not really a matter of typing, but a matter of > grouping similar children. It does not really matter if foo[1] is > deleted while foo[2] still exists, and it does not really matter if the > next object created will be foo[1] or foo[3]. > > While we do not have any example, QOM could support true array > properties, e.g. with type intList. > > Also note that while foo[*] was a generalization of MemoryRegion code, > the same idea has also existed forever for devices. > /machine/peripheral_anon and /machine/unattached do not currently use > automatic array-ification via foo[*], but they could. Let me try to paraphrase / further explain your view, to make sure I got it. "Automatic arrayification" isn't about array-valued properties, it's a convenience feature for creating a bunch of properties with a common type, accessors and so forth, named in a peculiar way: "foo[0]", "foo[1]", ... The feature saves the caller the trouble of generating the names. That's all there is to it. Once created, QOM assumes no particular relation between the properties. Weird: if you create a "foo[2]", then three "foo[*]", the three become "foo[0]", "foo[1]", "foo[3]". Correct so far? If yes, then I retract my "isn't this type matter" remark: it isn't, it's just a fancy way to generate names. However, I now have a different one: should we really bake fancy ways to generate names into object_property_add()? Wouldn't having a separate name generator be cleaner? And yet another one: the special treatment of names ending with "[*]" appears to be entirely undocumented! Review fail. >>> If you just want to call id_wellformed() for -object / object-add, I >>> won't object to restricting it beyond the necessary, but it'll lead to >>> two places doing validity checks for QOM. >> >> id_wellformed() is *already* called for -object and HMP object-add. >> That's exactly my point! >> >> Please reread my explanation, and if it's insufficient, ask for >> clarification. >> >> Subject: IDs in QOM (was: [PATCH] util: Emancipate id_wellformed() >> from QemuOpts) >> Date: Wed, 01 Oct 2014 14:33:47 +0200 >> Message-ID: <87iok46kb8....@blackfin.pond.sub.org> > > I think it is okay to keep calling id_wellformed(), since it covers the > QOM-specific constraint that slashes must be outlawed. It just makes > the children of /objects a bit more restricted in their naming, but that > is harmless because object_del can only delete objects created with > object_add. Why is it a good idea have two separate restrictions on property names? A loser one that applies always (anything but '\0' and '/'), and a stricter one that applies sometimes (letters, digits, '-', '.', '_', starting with a letter). If yes, how is "sometimes" defined? Are -object and object_add the only ways to create children of /objects? Hmm, I'm afraid my working definition of the loser one is incorrect. It's actually "anything but '\0' and '/' not ending with '[*]'.
