From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>
Subject: Re: [PATCH v8 21/21] libxl: add support for migrating
 HVM guests without a device model
Date: Thu, 26 Nov 2015 19:10:56 +0100
Message-ID: <56574B30.20700@citrix.com>
References: <1446825955-11842-1-git-send-email-roger.pau@citrix.com>
	<1446825955-11842-22-git-send-email-roger.pau@citrix.com>
	<56437789.40905@citrix.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
Received: from mail6.bemta5.messagelabs.com ([195.245.231.135])
	by lists.xen.org with esmtp (Exim 4.72)
	(envelope-from <prvs=765cef165=roger.pau@citrix.com>)
	id 1a210t-0008H5-Uz
	for xen-devel@lists.xenproject.org; Thu, 26 Nov 2015 18:11:24 +0000
In-Reply-To: <56437789.40905@citrix.com>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: Andrew Cooper <andrew.cooper3@citrix.com>, xen-devel@lists.xenproject.org
Cc: Ian Jackson <ian.jackson@eu.citrix.com>, Wei Liu <wei.liu2@citrix.com>, Ian Campbell <ian.campbell@citrix.com>
List-Id: xen-devel@lists.xenproject.org

El 11/11/15 a les 18.14, Andrew Cooper ha escrit:
> On 06/11/15 16:05, Roger Pau Monne wrote:
>> diff --git a/tools/libxl/libxl_stream_write.c b/tools/libxl/libxl_stream_write.c
>> index 52a60d7..0a6eaf9 100644
>> --- a/tools/libxl/libxl_stream_write.c
>> +++ b/tools/libxl/libxl_stream_write.c
>> @@ -232,6 +232,9 @@ void libxl__stream_write_start(libxl__egc *egc,
>>              stream->emu_sub_hdr.id = EMULATOR_QEMU_UPSTREAM;
>>              break;
>>  
>> +        case LIBXL_DEVICE_MODEL_VERSION_NONE:
>> +            break;
>> +
> 
> This (in principle) leaves stream->emu_sub_hdr.id uninitialised
> (although its value will be zero because of libxl__stream_write_init()).
> 
> I would be tempted to (ab)use EMULATOR_UNKNOWN here and have
> setup_emulator_write() assert id != UNKNOWN, to catch calls which slip
> through the cracks.

This seems fine to me and I've implemented it.

> 
>>          default:
>>              rc = ERROR_FAIL;
>>              LOG(ERROR, "Unknown emulator for HVM domain");
>> @@ -359,6 +362,12 @@ static void write_emulator_xenstore_record(libxl__egc *egc,
>>      char *buf = NULL;
>>      uint32_t len = 0;
>>  
>> +    if (libxl__device_model_version_running(gc, dss->domid) ==
>> +        LIBXL_DEVICE_MODEL_VERSION_NONE) {
>> +        emulator_xenstore_record_done(egc, stream);
>> +        return;
>> +    }
>> +
> 
> libxl__device_model_version_running() performs a xenstore action, which
> is a steep overhead for constant information.
> 
> It would be better to introduce a new field in libxl__stream_write_state
> and cache libxl__device_model_version_running() once in
> libxl__stream_write_start().  You can then also use that for an
> assertion in setup_emulator_write()

Right, so I've ended up adding two asserts in setup_emulator_write:

assert(stream->emu_sub_hdr.id != EMULATOR_UNKNOWN);
assert(stream->device_model_version != LIBXL_DEVICE_MODEL_VERSION_NONE);

Roger.