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

[Tetsuya Mukawa]

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.

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