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From: Eric Blake <eblake@redhat.com>
Message-ID: <e728135e-1996-207b-e7bb-df760cc7abff@redhat.com>
Date: Fri, 31 Aug 2018 10:01:15 -0500
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Subject: Re: [Qemu-devel] [PATCH v2 14/20] memory-device: ids of virtio
 based devices are special
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To: David Hildenbrand <david@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: qemu-devel@nongnu.org, "Michael S . Tsirkin" <mst@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net>, Eduardo Habkost <ehabkost@redhat.com>, Markus Armbruster <armbru@redhat.com>, Pankaj Gupta <pagupta@redhat.com>, Luiz Capitulino <lcapitul@redhat.com>

On 08/31/2018 06:18 AM, David Hildenbrand wrote:

>>>>> -                error_setg(errp, "address range conflicts with '%s'", d->id);
>>>>> +                error_setg(errp, "address range conflicts with '%s'",
>>>>> +                           id ? id : 0);
>>>>
>>>> What's that 'id ? id : 0' trick for?
>>>
>>> 0 -> "", then it actually makes sense :)
>>>

> 
> qemu-system-x86_64: -device pc-dimm,memdev=mem1,addr=0x140000000:
> address range conflicts with '(null)'
> 
> (I thought providing NULL would lead to a crash, but it is actually
> handled properly)

Well, glibc handles it. But POSIX says it is undefined, and there are 
other libc where it indeed crashes.  It's better to pass an explicit 
non-null placeholder than to rely on glibc turning NULL into "(null)".

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org