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

[Yuanhan Liu]

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?

	--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