From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH RFC] virtio-pci: new config layout: using memory BAR
Date: Wed, 29 May 2013 15:41:09 +0200
Message-ID: <51A60575.1090407@redhat.com>
References: <20130528160342.GA29915@redhat.com> <87bo7vvxej.fsf@codemonkey.ws>
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	<20130529132430.GA9363@redhat.com>
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, Anthony Liguori <aliguori@us.ibm.com>, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, Stefan Hajnoczi <stefanha@redhat.com>, KONRAD Frederic <fred.konrad@greensocs.com>
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Il 29/05/2013 15:24, Michael S. Tsirkin ha scritto:
> You expect a compiler to pad this structure:
> 
> struct foo {
> 	uint8_t a;
> 	uint8_t b;
> 	uint16_t c;
> 	uint32_t d;
> };
> 
> I'm guessing any compiler that decides to waste memory in this way
> will quickly get dropped by users and then we won't worry
> about building QEMU with it.

You know the virtio-pci config structures are padded, but not all of
them are.  For example, virtio_balloon_stat is not padded and indeed has
an __attribute__((__packed__)) in the spec.

For this reason I prefer to have the attribute everywhere.  So people
don't have to wonder why it's here and not there.

Paolo