From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:53818)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1RW6w7-00077d-8q
	for qemu-devel@nongnu.org; Thu, 01 Dec 2011 08:44:28 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1RW6w1-0002tj-M7
	for qemu-devel@nongnu.org; Thu, 01 Dec 2011 08:44:27 -0500
Received: from mail-yx0-f173.google.com ([209.85.213.173]:57244)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1RW6w1-0002tW-GA
	for qemu-devel@nongnu.org; Thu, 01 Dec 2011 08:44:21 -0500
Received: by yenq3 with SMTP id q3so2229469yen.4
	for <qemu-devel@nongnu.org>; Thu, 01 Dec 2011 05:44:21 -0800 (PST)
Message-ID: <4ED784B3.8060800@codemonkey.ws>
Date: Thu, 01 Dec 2011 07:44:19 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
References: <1322687028-29714-1-git-send-email-aliguori@us.ibm.com>	<1322687028-29714-8-git-send-email-aliguori@us.ibm.com>
	<4ED76325.6080305@redhat.com>
In-Reply-To: <4ED76325.6080305@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 07/18] qom: add link properties
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Avi Kivity <avi@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Peter Maydell <peter.maydell@linaro.org>, Anthony Liguori <aliguori@us.ibm.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, Jan Kiszka <jan.kiszka@siemens.com>, qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>, Luiz Capitulino <lcapitulino@redhat.com>

On 12/01/2011 05:21 AM, Avi Kivity wrote:
> On 11/30/2011 11:03 PM, Anthony Liguori wrote:
>> Links represent an ephemeral relationship between devices.  They are meant to
>> replace the qdev concept of busses by allowing more informal relationships
>> between devices.
>
> So, links are equivalent to pointers?

Yup.  Once we have qom inheritance (next stage), we can have a link<PCIDevice> 
property and you'll be able to set it to an E1000State with the appropriate 
casting and error checking taking place.

>> Links are fairly limited in their usefulness without implementing QOM-style
>> subclassing and interfaces.
>>
>>
>> +static void qdev_get_link_property(DeviceState *dev, Visitor *v, void *opaque,
>> +                                   const char *name, Error **errp)
>> +{
>> +    DeviceState **child = opaque;
>> +    gchar *path;
>> +
>> +    if (*child) {
>> +        path = qdev_get_canonical_path(*child);
>> +        visit_type_str(v,&path, name, errp);
>> +        g_free(path);
>> +    } else {
>> +        path = (gchar *)"";
>
> If gchar != char, this is wrong.  Also, you're converting a const
> pointer into a non-const pointer, discarding type safety.

I'll address this later in the thread.

>> +        visit_type_str(v,&path, name, errp);
>> +    }
>
> Shouldn't this be visit_type_link()?

link isn't a primitive type for visitors.   visit_type_link() would just call 
visit_type_str() so I don't think there's a ton of value in introducing the 
extra layer.

The accessors are the only places that should be marshaling links.

Regards,

Anthony Liguori

>