From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Borntraeger <borntraeger@de.ibm.com>
Subject: Re: [PATCH 4/4] KVM: s390: Add a channel I/O based virtio transport
 driver.
Date: Thu, 13 Dec 2012 12:13:55 +0100
Message-ID: <50C9B873.5090800@de.ibm.com>
References: <1355330201-36481-1-git-send-email-cornelia.huck@de.ibm.com> <1355330201-36481-5-git-send-email-cornelia.huck@de.ibm.com> <50C8CD8F.2000909@suse.de> <50C8E52A.1@de.ibm.com> <051FA3EB-2FCA-4AEB-914C-DD19A8F17572@suse.de>
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To: Alexander Graf <agraf@suse.de>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>, Marcelo Tosatti <mtosatti@redhat.com>, Gleb Natapov <gleb@redhat.com>, KVM <kvm@vger.kernel.org>, linux-s390 <linux-s390@vger.kernel.org>, Carsten Otte <cotte@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Sebastian Ott <sebott@linux.vnet.ibm.com>
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On 13/12/12 12:06, Alexander Graf wrote:
> 
> On 12.12.2012, at 21:12, Christian Borntraeger wrote:
> 
>> On 12/12/12 19:31, Alexander Graf wrote:
>> +static inline long do_kvm_notify(struct subchannel_id schid,
>>>> +                 unsigned long queue_index)
>>>> +{
>>>> +    register unsigned long __nr asm("1") = KVM_S390_VIRTIO_CCW_NOTIFY;
>>>> +    register struct subchannel_id __schid asm("2") = schid;
>>>
>>> How does the compiler know that the struct fits within a register?
>>>
>>
>> Well it knows that sizeof struct subchannel_id is 4.
> 
> How so? The asm/ccwdev.h header simply says
> 
>   struct subchannel_id;

see original patch:

>>> +#include <asm/cio.h>
>>> +#include <asm/ccwdev.h>
>>> +#include <asm/schid.h>
>>> +
>>> +/*
>>> + * virtio related functions
>>> + */
>>> +

asm/schid.h includes uapi/asm/schid.h and that contains the definition.