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Subject: Re: [PATCH 1/4] vdpa: introduce config op to get valid iova range
To:     "Michael S. Tsirkin" <mst@redhat.com>, Eli Cohen <eli@mellanox.com>
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <2d1e6278-e57e-c340-399e-40ff102c74a3@redhat.com>
Date:   Tue, 11 Aug 2020 10:53:09 +0800
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On 2020/8/10 下午8:05, Michael S. Tsirkin wrote:
> On Thu, Aug 06, 2020 at 03:43:54PM +0300, Eli Cohen wrote:
>> On Thu, Aug 06, 2020 at 08:29:22AM -0400, Michael S. Tsirkin wrote:
>>> On Thu, Aug 06, 2020 at 03:03:55PM +0300, Eli Cohen wrote:
>>>> On Wed, Aug 05, 2020 at 08:51:56AM -0400, Michael S. Tsirkin wrote:
>>>>> On Wed, Jun 17, 2020 at 11:29:44AM +0800, Jason Wang wrote:
>>>>>> This patch introduce a config op to get valid iova range from the vDPA
>>>>>> device.
>>>>>>
>>>>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>>>>>> ---
>>>>>>   include/linux/vdpa.h | 14 ++++++++++++++
>>>>>>   1 file changed, 14 insertions(+)
>>>>>>
>>>>>> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
>>>>>> index 239db794357c..b7633ed2500c 100644
>>>>>> --- a/include/linux/vdpa.h
>>>>>> +++ b/include/linux/vdpa.h
>>>>>> @@ -41,6 +41,16 @@ struct vdpa_device {
>>>>>>   	unsigned int index;
>>>>>>   };
>>>>>>   
>>>>>> +/**
>>>>>> + * vDPA IOVA range - the IOVA range support by the device
>>>>>> + * @start: start of the IOVA range
>>>>>> + * @end: end of the IOVA range
>>>>>> + */
>>>>>> +struct vdpa_iova_range {
>>>>>> +	u64 start;
>>>>>> +	u64 end;
>>>>>> +};
>>>>>> +
>>>>>
>>>>> This is ambiguous. Is end in the range or just behind it?
>>>>> How about first/last?
>>>> It is customary in the kernel to use start-end where end corresponds to
>>>> the byte following the last in the range. See struct vm_area_struct
>>>> vm_start and vm_end fields
>>> Exactly my point:
>>>
>>> include/linux/mm_types.h:       unsigned long vm_end;           /* The first byte after our end address
>>>
>>> in this case Jason wants it to be the last byte, not one behind.
>>>
>>>
>> Maybe start, size? Not ambiguous, and you don't need to do annoying
>> calculations like size = last - start + 1
> Size has a bunch of issues: can overlap, can not cover the entire 64 bit
> range. The requisite checks are arguably easier to get wrong than
> getting the size if you need it.


Yes, so do you still prefer first/last or just begin/end which is 
consistent with iommu_domain_geometry?

Thanks


>