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Re: [Qemu-devel] [PATCH v4 25/28] qapi: Make input visitors detect unvis

From: Markus Armbruster
Subject: Re: [Qemu-devel] [PATCH v4 25/28] qapi: Make input visitors detect unvisited list tails
Date: Sun, 05 Mar 2017 09:06:07 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux)

Eric Blake <address@hidden> writes:

> On 03/03/2017 01:50 PM, Markus Armbruster wrote:
>> Eric Blake <address@hidden> writes:
>>> On 03/03/2017 06:32 AM, Markus Armbruster wrote:
>>>> Fix the design flaw demonstrated in the previous commit: new method
>>>> check_list() lets input visitors report that unvisited input remains
>>>> for a list, exactly like check_struct() lets them report that
>>>> unvisited input remains for a struct or union.
>>>> Implement the method for the qobject input visitor (straightforward),
>>>> and the string input visitor (less so, due to the magic list syntax
>>>> there).  The opts visitor's list magic is even more impenetrable, and
>>>> all I can do there today is a stub with a FIXME comment.  No worse
>>>> than before.
>>>> Signed-off-by: Markus Armbruster <address@hidden>
>>>> ---
>>> Didn't I already review this one?
>>> Ah, there's my R-b:
>>> https://lists.gnu.org/archive/html/qemu-devel/2017-02/msg07614.html
>>>> --- a/qapi/qobject-input-visitor.c
>>>> +++ b/qapi/qobject-input-visitor.c
>>>> @@ -51,7 +51,8 @@ static QObjectInputVisitor *to_qiv(Visitor *v)
>>>>      return container_of(v, QObjectInputVisitor, visitor);
>>>>  }
>>>> -static const char *full_name(QObjectInputVisitor *qiv, const char *name)
>>>> +static const char *full_name_nth(QObjectInputVisitor *qiv, const char 
>>>> *name,
>>>> +                                 int n)
>>>>  {
> No function comment, so the _nth and int n are guesses on their meaning...
>>> If I'm reading this right, your use of n-- in the loop followed by the
>>> post-condition is to assert that QSLIST_FOREACH() iterated n times, but
>>> lets see what callers pass for n:
>> At least @n times.
> Ah, as in 'use first available result' or 'iterate at least once', based
> on our callers, but could also mean 'iterate at least twice' for a
> caller that passes 2.
>>> the other passes 1.  No other calls.  Did we really need an integer,
>>> where we use n--, or would a bool have done as well?
>> Since I actually use only 0 and 1, a bool would do, but would it make
>> the code simpler?
> I don't know that a bool would be any simpler,
>>> At any rate, since I've already reviewed it once, you can add R-b, but
>>> we may want a followup to make it less confusing.
>> Would renaming the function to full_name_but_n() help?
> Or even keep the name unchanged, but add function comments describing
> what 'n' means.

Makes sense.  I'll do it on top to avoid delaying merge of this series
and the other stuff that depends on it.

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