From: "Kővágó Zoltán" <dirty.ice.hu@gmail.com>
To: Markus Armbruster <armbru@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>
Cc: "Kevin Wolf" <kwolf@redhat.com>,
"László Ersek" <lersek@redhat.com>,
"Michael Roth" <mdroth@linux.vnet.ibm.com>,
qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v2 2/6] qapi: support nested structs in OptsVisitor
Date: Wed, 17 Jun 2015 14:11:49 +0200 [thread overview]
Message-ID: <55816405.7090502@gmail.com> (raw)
In-Reply-To: <87bngea8hi.fsf@blackfin.pond.sub.org>
2015-06-17 13:18 keltezéssel, Markus Armbruster írta:
> Copying Kevin because similar issues exist in the block layer.
>
> Gerd Hoffmann <kraxel@redhat.com> writes:
>
>> On Mi, 2015-06-17 at 09:50 +0200, Markus Armbruster wrote:
>>> Copying László because his fingerprints are on OptsVisitor.
>>>
>>> "Kővágó, Zoltán" <dirty.ice.hu@gmail.com> writes:
>>>
>>>> The current OptsVisitor flattens the whole structure, if there are
>>>> same named
>>>> fields under different paths (like `in' and `out' in `Audiodev'),
>>>> the current
>>>> visitor can't cope with them (for example setting
>>>> frequency=44100' will set the
>>>> in's frequency to 44100 and leave out's frequency unspecified).
>>>>
>>>> This patch fixes it, by the following changes:
>>>> 1) Specifying just the field name will apply to all fields that has the
>>>> specified name (this means it would set both in's and out's frequency to
>>>> 44100 in the above example).
>
> What if they have different types?
>
> What if one of them can't take the value?
Currently it will error out, requiring the user to be more explicit.
Probably not the best solution, but I can't really think of a better
solution. (If we would ignore invalid values that would be very
confusing imho.)
>>>> 2) Optionally user can specify the path in the hierarchy. Names
>>>> are separated by
>>>> a dot (e.g. `in.frequency', `foo.bar.something', etc). The user need not
>>>> specify the whole path, only the last few components
>>>> (i.e. `bar.something' is
>>>> equivalent to `foo.bar.something' if only `foo' has a `bar'
>>>> field). This way
>>>> 1) is just a special case of this when only the last component
>>>> is specified.
>>>> 3) In case of an ambiguity (e.g
>>>> frequency=44100,in.frequency=8000') the longest
>>>> matching (the most specific) path wins (so in this example,
>>>> in's frequency
>>>> would become 8000, because `in.frequency' is more specific that
>>>> frequency',
>>>> and out's frequency would become 44100, because only
>>>> frequency' matches it).
>
> The current rule for multiple assignments is "last one wins". E.g. in
>
> -drive if=none,file=tmp.img,file=tmp.qcow2
>
> file=tmp.qcow2 wins.
>
> If I understand correctly, this patch amends the rule to "last most
> specific one wins". Correct?
Yes. (But I didn't really checked that as I didn't know about the "last
one win", and just thought it's an artifact of the current implementation.)
>>> Can you explain why the complexity is needed, i.e. why we can't just
>>> require full paths always?
>>
>> Keeping the short names is required for -netdev backward compatibility.
>
> I suspect mostly because NetLegacy and Netdev aren't flat unions.
> Could be self-inflicted pain.
>
> What about flattening them instead? Assuming that's possible; I'd have
> to try.
>
>> Restricting to short or full (i.e. something= or foo.bar.something=, but
>> disallow bar.something=) should not be a problem. I'm not sure this
>> simplifies things much though. We have to build the full path anyway,
>> and I think bar.something= is just a convenient thing we get almost for
>> free ...
>
> We've been bitten by convenience features before. Adding them tends to
> be cheap, but maintaining compatibility can become a terrible headache.
>
next prev parent reply other threads:[~2015-06-17 12:11 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-16 12:49 [Qemu-devel] [PATCH v2 0/6] -audiodev option Kővágó, Zoltán
2015-06-16 12:49 ` [Qemu-devel] [PATCH v2 1/6] qapi: qapi for audio backends Kővágó, Zoltán
2015-06-17 7:46 ` Markus Armbruster
2015-06-17 10:54 ` Kővágó Zoltán
2015-06-17 11:48 ` Markus Armbruster
2015-06-17 12:07 ` Kővágó Zoltán
2015-06-17 13:37 ` Markus Armbruster
2015-06-17 13:53 ` Kővágó Zoltán
2015-06-17 16:06 ` Markus Armbruster
2015-06-18 0:21 ` Kővágó Zoltán
2015-06-18 8:51 ` Markus Armbruster
2015-06-17 15:50 ` Eric Blake
2015-06-16 12:49 ` [Qemu-devel] [PATCH v2 2/6] qapi: support nested structs in OptsVisitor Kővágó, Zoltán
2015-06-17 7:50 ` Markus Armbruster
2015-06-17 8:41 ` Gerd Hoffmann
2015-06-17 11:01 ` Kővágó Zoltán
2015-06-17 11:50 ` Markus Armbruster
2015-06-17 15:47 ` Eric Blake
2015-06-17 11:18 ` Markus Armbruster
2015-06-17 12:11 ` Kővágó Zoltán [this message]
2015-06-17 13:41 ` Markus Armbruster
2015-06-17 14:02 ` Kővágó Zoltán
2015-06-17 16:10 ` Markus Armbruster
2015-06-16 12:49 ` [Qemu-devel] [PATCH v2 3/6] opts: do not print separator before first item in qemu_opts_print Kővágó, Zoltán
2015-06-17 7:53 ` Markus Armbruster
2015-06-17 9:02 ` Kevin Wolf
2015-06-16 12:49 ` [Qemu-devel] [PATCH v2 4/6] qapi: AllocVisitor Kővágó, Zoltán
2015-06-17 7:56 ` Markus Armbruster
2015-06-17 12:01 ` Kővágó Zoltán
2015-06-17 13:42 ` Markus Armbruster
2015-06-16 12:49 ` [Qemu-devel] [PATCH v2 5/6] audio: use qapi AudioFormat instead of audfmt_e Kővágó, Zoltán
2015-06-17 8:01 ` Markus Armbruster
2015-06-17 11:05 ` Kővágó Zoltán
2015-06-17 11:51 ` Markus Armbruster
2015-06-17 16:01 ` Eric Blake
2015-06-16 12:49 ` [Qemu-devel] [PATCH v2 6/6] audio: -audiodev command line option Kővágó, Zoltán
2015-06-17 8:13 ` Markus Armbruster
2015-06-17 11:18 ` Kővágó Zoltán
2015-06-17 12:27 ` Markus Armbruster
2015-06-17 13:25 ` Kővágó Zoltán
2015-06-17 16:13 ` Markus Armbruster
2015-06-18 6:54 ` Gerd Hoffmann
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