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From: Markus Armbruster <armbru@redhat.com>
References: <1504541267-36954-1-git-send-email-pradeep.jagadeesh@huawei.com>
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Date: Fri, 08 Sep 2017 14:51:29 +0200
In-Reply-To: <w51mv652zmt.fsf@maestria.local.igalia.com> (Alberto Garcia's
	message of "Fri, 08 Sep 2017 13:33:46 +0200")
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Subject: Re: [Qemu-devel] [PATCH v10 5/6] fsdev: QMP interface for throttling
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To: Alberto Garcia <berto@igalia.com>
Cc: Pradeep Jagadeesh <pradeepkiruvale@gmail.com>, qemu-devel@nongnu.org, greg kurz <groug@kaod.org>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Pradeep Jagadeesh <pradeep.jagadeesh@huawei.com>, jani kokkonen <jani.kokkonen@huawei.com>

Alberto Garcia <berto@igalia.com> writes:

> On Fri 08 Sep 2017 12:02:14 PM CEST, Markus Armbruster wrote:
>
>>> +    fse = get_fsdev_fsentry(arg->has_id ? arg->id : NULL);
>>
>> !arg->has_id implies !arg->id.
>
> Hey Markus,
>
> I have the impression that I've also written code that never uses
> arg->foo when arg->has_foo is false.
>
> Can we then assume that to be NULL/0 in all cases? Also for other data
> types (int, bool, ...)?

QAPI code always passes zero FOOs along with false has_FOOs.  Anything
that doesn't is a bug.  This is particular important when FOO is a
pointer; we don't want to pass around pointers pointing to random junk
in the hope that everybody will obediently check their has_FOO before
dereferencing.

Other code might not always be as well-behaved.  In random context,
checking has_FOO is probably safer.

I still want to eliminate has_FOO for pointer-valued FOO.  So much to
do, so little time!