From mboxrd@z Thu Jan  1 00:00:00 1970
From: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Subject: Re: [Qemu-devel] [PATCH v6 18/33] dimm: get mapped memory region from
 DIMMDeviceClass->get_memory_region
Date: Mon, 2 Nov 2015 17:18:25 +0800
Message-ID: <56372A61.5070807@linux.intel.com>
References: <1446184587-142784-1-git-send-email-guangrong.xiao@linux.intel.com>
 <1446184587-142784-19-git-send-email-guangrong.xiao@linux.intel.com>
 <56349D6E.8010803@virtuozzo.com> <5634CCEB.4070004@linux.intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Cc: ehabkost@redhat.com, kvm@vger.kernel.org, mst@redhat.com,
	gleb@kernel.org, mtosatti@redhat.com, qemu-devel@nongnu.org,
	stefanha@redhat.com, dan.j.williams@intel.com, rth@twiddle.net
To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
	pbonzini@redhat.com, imammedo@redhat.com
Return-path: <kvm-owner@vger.kernel.org>
Received: from mga11.intel.com ([192.55.52.93]:14324 "EHLO mga11.intel.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751310AbbKBJ2N (ORCPT <rfc822;kvm@vger.kernel.org>);
	Mon, 2 Nov 2015 04:28:13 -0500
In-Reply-To: <5634CCEB.4070004@linux.intel.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>



On 10/31/2015 10:15 PM, Xiao Guangrong wrote:
>
>
> On 10/31/2015 06:52 PM, Vladimir Sementsov-Ogievskiy wrote:
>> On 30.10.2015 08:56, Xiao Guangrong wrote:
>>> Curretly, the memory region of backed memory is directly mapped to
>>> guest's address space, however, it is not true for nvdimm device
>>>
>>> This patch let dimm device realize this fact and use
>>> DIMMDeviceClass->get_memory_region method to get the mapped memory
>>> region
>>>
>>> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>>> ---
>>>   hw/mem/dimm.c | 3 ++-
>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/hw/mem/dimm.c b/hw/mem/dimm.c
>>> index 4a63409..498d380 100644
>>> --- a/hw/mem/dimm.c
>>> +++ b/hw/mem/dimm.c
>>> @@ -377,8 +377,9 @@ static void dimm_get_size(Object *obj, Visitor *v, void *opaque,
>>>       int64_t value;
>>>       MemoryRegion *mr;
>>>       DIMMDevice *dimm = DIMM(obj);
>>> +    DIMMDeviceClass *ddc = DIMM_GET_CLASS(obj);
>>> -    mr = host_memory_backend_get_memory(dimm->hostmem, errp);
>>> +    mr = ddc->get_memory_region(dimm);
>>>       value = memory_region_size(mr);
>>>       visit_type_int(v, &value, name, errp);
>>
>> Isn't it better to add Error** parameter to get_memory_region and not mix returning error in errp
>> parameter and aborting through &error_abort?
>>
>
> Yes, it's better, will do. Thanks for your suggestion.

Vladimir,

After checking the current code, the @errp in pc-dimm's get_memory_region() is useless
and all its caller did not check the return value as they assumed the backend memory of
pc-dimm is always properly initialized.

So we catch the error condition internally instead of propagating it to the caller:

  static MemoryRegion *pc_dimm_get_memory_region(DIMMDevice *dimm)
  {
-    return host_memory_backend_get_memory(dimm->hostmem, &error_abort);
+    Error *local_err = NULL;
+    MemoryRegion *mr;
+
+    mr = host_memory_backend_get_memory(dimm->hostmem, &local_err);
+
+    /*
+     * plug a pc-dimm device whose backend memory was not properly
+     * initialized?
+     */
+    assert(!local_err && mr);
+    return mr;
  }

please review it in the new version i have CCed you.

Thanks for your review.