From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:54561)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1QyP85-0004Bw-LH
	for qemu-devel@nongnu.org; Tue, 30 Aug 2011 10:17:30 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1QyP84-0007B3-LN
	for qemu-devel@nongnu.org; Tue, 30 Aug 2011 10:17:29 -0400
Received: from mail-yw0-f45.google.com ([209.85.213.45]:37298)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1QyP84-0007Am-Is
	for qemu-devel@nongnu.org; Tue, 30 Aug 2011 10:17:28 -0400
Received: by ywf9 with SMTP id 9so6347159ywf.4
	for <qemu-devel@nongnu.org>; Tue, 30 Aug 2011 07:17:27 -0700 (PDT)
Message-ID: <4E5CF0F4.2030208@codemonkey.ws>
Date: Tue, 30 Aug 2011 09:17:24 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
References: <4E5BE7AF.5020906@linux.vnet.ibm.com>	<1314646068-31438-1-git-send-email-mdroth@linux.vnet.ibm.com>
	<CAJSP0QWY6ofQYpvHLFaO8Ar_UAUno3JEMXJL0yqVzOx5BFimtg@mail.gmail.com>
In-Reply-To: <CAJSP0QWY6ofQYpvHLFaO8Ar_UAUno3JEMXJL0yqVzOx5BFimtg@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH] Add CONFIG_QEMU_TIMER to handle
 qemu-timer-common.o dep
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: Stefan Hajnoczi <stefanha@gmail.com>
Cc: blauwirbel@gmail.com, xscript@gmx.net, Michael Roth <mdroth@linux.vnet.ibm.com>, qemu-devel@nongnu.org

On 08/30/2011 04:22 AM, Stefan Hajnoczi wrote:
> On Mon, Aug 29, 2011 at 8:27 PM, Michael Roth<mdroth@linux.vnet.ibm.com>  wrote:
>> @@ -380,7 +381,6 @@ else
>>   trace-obj-y = trace.o
>>   ifeq ($(TRACE_BACKEND),simple)
>>   trace-obj-y += simpletrace.o
>> -user-obj-y += qemu-timer-common.o
>>   endif
>>   endif
>
> Now that we have a concrete patch to look at I think this approach is
> problematic.  There are several subsystems in QEMU which might be
> built outside the main qemu binary for qemu-io, qemu-img, qemu-ga,
> etc.

Er, but qemu-timer cannot possibly be used by qemu-io/qemu-img.

Is this all dummy magic in order to let qemu-io build even though simple 
tracing won't work?

Perhaps we should look at making the tracing backends dynamic instead of 
static?

Regards,

Anthony Liguori

>
> Each subsystem should explicitly include its dependencies (e.g.
> subsys-obj-y += qemu-timer-common.o or subsys-obj-y +=
> $(more-fundamental-subsys)) so that it can be easily used by a target.
>   If this is not done then there are two disadvantages:
> 1. We spray dependency information across the makefiles instead of
> keeping them contained with the subsystem that has the dependency
> requirement.
> 2. We duplicate the dependencies across each target in the form of
> conditional objects:
> x-obj-$(CONFIG_MY_DEPENDENCY) += ...
>
> If QEMU is split up into libraries then having an explicit list of
> dependencies for each subsystem will be very useful, whereas the
> CONFIG_* approach doesn't collect that information in one place.
>
> So I think explicit subsys-obj-y += qemu-timer-common.o together with
> $(sort) during the link stage actually allows for a cleaner build
> system.  I prefer that approach.
>
> Stefan
>