[dpdk-dev] [PATCH v4 1/2] vhost: Add callback and private data for vhost PMD

[Tetsuya Mukawa]

On 2015/11/19 14:45, Yuanhan Liu wrote:
> On Thu, Nov 19, 2015 at 02:14:13PM +0900, Tetsuya Mukawa wrote:
>> On 2015/11/19 12:33, Yuanhan Liu wrote:
>>> On Thu, Nov 19, 2015 at 12:13:38PM +0900, Tetsuya Mukawa wrote:
>>>> On 2015/11/19 11:18, Yuanhan Liu wrote:
>>>>> On Thu, Nov 19, 2015 at 11:03:50AM +0900, Tetsuya Mukawa wrote:
>>>>>> On 2015/11/17 22:29, Yuanhan Liu wrote:
>>>>>>> On Fri, Nov 13, 2015 at 02:20:30PM +0900, Tetsuya Mukawa wrote:
>>>>>>>> These variables are needed to be able to manage one of virtio devices
>>>>>>>> using both vhost library APIs and vhost PMD.
>>>>>>>> For example, if vhost PMD uses current callback handler and private data
>>>>>>>> provided by vhost library, A DPDK application that links vhost library
>>>>>>>> cannot use some of vhost library APIs.
>>>>>>> Can you be more specific about this?
>>>>>>>
>>>>>>> 	--yliu
>>>>>> How about like below?
>>>>>>
>>>>>> commit log:
>>>>>> Currently, when virtio device is created and destroyed, vhost library
>>>>>> will call one of callback handlers.
>>>>>> The vhost PMD need to use this pair of callback handlers to know which
>>>>>> virtio devices are connected actually.
>>>>>> Because we can register only one pair of callbacks to vhost library, if
>>>>>> the PMD use it, DPDK applications
>>>>>> cannot have a way to know the events.
>>>>> Will (and why) the two co-exist at same time?
>>>> Yes it is. Sure, I will describe below in commit log.
>>>>
>>>> Because we cannot map some of vhost library APIs to ethdev APIs, in some
>>>> cases, we still
>>>> need to use vhost library APIs for a port created by the vhost PMD. One
>>>> of example is
>>>> rte_vhost_enable_guest_notification().
>>> I don't get it why it has something to do with a standalone PMD callback.
>>> And if you don't call rte_vhost_enable_guest_notification() inside vhost
>>> PMD, where else can you call that? I mean, you can't start vhost-pmd
>>> and vhost-swithc in the mean time, right?
>> No it's not true, even after connecting to virtio-net device, you can
>> change the flag.
>> It's just a hint for virtio-net driver, and it will be used while queuing.
>> (We may be able to change the flag, even while sending or receiving packets)
>>
>>> And, pmd callback and the old notify callback will not exist at same
>>> time in one case, right? If so, why is that needed?
>>>
>>> BTW, if it's a MUST, would you provide a specific example?
>> Actually, this patch is not a MUST.
>>
>> But still the users need callback handlers to know when virtio-net
>> device is connected or disconnected.
>> This is because the user can call rte_vhost_enable_guest_notification()
>> only while connection is established.
> What does "the user" mean? Is there a second user of vhost lib besides
> vhost PMD, that he has to interact with those connected devices? If so,
> how?

Sorry, my English is wrong.
Not a second user.

For example, If DPDK application has a port created by vhost PMD, then
needs to call rte_vhost_enable_guest_notification() to the port.
DPDK application needs to know when virtio-net device is connected or
disconnected, because the function is only valid while connecting.
But without callback handler, DPDK application cannot know it.

This is what I wanted to explain.

Thanks,
Tetsuya

> 	--yliu
>> Probably we can use link status changed callback of the PMD for this
>> purpose.
>> (The vhost PMD will notice DPDK application using link status callback)
>>
>> But I am not sure whether we need to implement link status changed
>> callback for this purpose.
>> While processing this callback handler, the users will only calls vhost
>> library APIs that ethdev API cannot map, or store some variables related
>> with vhost library.
>> If so, this callback handler itself is specific for using vhost library.
>> And it may be ok that callback itself is implemented as one of vhost
>> library APIs.
>>
>> Tetsuya
>>
>>> 	--yliu
>>>> Thanks,
>>>> Tetsuya
>>>>
>>>>
>>>>> 	--yliu
>>>>>
>>>>>> This may break legacy DPDK
>>>>>> applications that uses vhost library.
>>>>>> To prevent it, this patch adds one more pair of callbacks to vhost
>>>>>> library especially for the vhost PMD.
>>>>>> With the patch, legacy applications can use the vhost PMD even if they
>>>>>> need additional specific handling
>>>>>> for virtio device creation and destruction.
>>>>>> For example, legacy application can call
>>>>>> rte_vhost_enable_guest_notification() in callbacks to change setting.
>>>>>>
>>>>>> Tetsuya