Re: vhost: add virtio configuration space access socket messages

["Liu, Changpeng" <changpeng.liu@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> Sent: Tuesday, February 26, 2019 8:32 PM
> To: Ilya Maximets <i.maximets@samsung.com>; Liu, Changpeng
> <changpeng.liu@intel.com>; dev@dpdk.org
> Cc: Stojaczyk, Dariusz <dariusz.stojaczyk@intel.com>; Bie, Tiwei
> <tiwei.bie@intel.com>; Wang, Zhihong <zhihong.wang@intel.com>; Jason Wang
> <jasowang@redhat.com>
> Subject: Re: vhost: add virtio configuration space access socket messages
> 
> 
> 
> On 2/26/19 9:42 AM, Ilya Maximets wrote:
> > On 26.02.2019 11:13, Liu, Changpeng wrote:
> >>
> >>
> >>> -----Original Message-----
> >>> From: Ilya Maximets [mailto:i.maximets@samsung.com]
> >>> Sent: Tuesday, February 26, 2019 3:39 PM
> >>> To: Liu, Changpeng <changpeng.liu@intel.com>; dev@dpdk.org
> >>> Cc: Stojaczyk, Dariusz <dariusz.stojaczyk@intel.com>;
> >>> maxime.coquelin@redhat.com; Bie, Tiwei <tiwei.bie@intel.com>; Wang,
> >>> Zhihong <zhihong.wang@intel.com>; Jason Wang <jasowang@redhat.com>
> >>> Subject: Re: vhost: add virtio configuration space access socket messages
> >>>
> >>> On 26.02.2019 10:01, Liu, Changpeng wrote:
> >>>>
> >>>>
> >>>>> -----Original Message-----
> >>>>> From: Ilya Maximets [mailto:i.maximets@samsung.com]
> >>>>> Sent: Monday, February 25, 2019 9:20 PM
> >>>>> To: Liu, Changpeng <changpeng.liu@intel.com>; dev@dpdk.org
> >>>>> Cc: Stojaczyk, Dariusz <dariusz.stojaczyk@intel.com>;
> >>>>> maxime.coquelin@redhat.com; Bie, Tiwei <tiwei.bie@intel.com>; Wang,
> >>>>> Zhihong <zhihong.wang@intel.com>; Jason Wang <jasowang@redhat.com>
> >>>>> Subject: Re: vhost: add virtio configuration space access socket messages
> >>>>>
> >>>>> On 25.02.2019 10:51, Changpeng Liu wrote:
> >>>>>> This patch adds new vhost user messages GET_CONFIG and SET_CONFIG
> >>>>>> used to get/set virtio device's PCI configuration space.
> >>>>>
> >>>>> Beside the fact that some additional description and reasoning required,
> >>>>> I do not see the usage of this feature. You're defining the flag
> >>>>> VHOST_USER_PROTOCOL_F_CONFIG, but it's never used. So, none of
> dpdk
> >>> vhost
> >>>>> backends (vdpa, vhost-user) will use this feature.
> >>>>> You, probably, missed adding it to VHOST_USER_PROTOCOL_FEATURES or
> >>>>> VDPA_SUPPORTED_PROTOCOL_FEATURES.
> >>>>>
> >>>>>  From the other side, current implementation forces application to
> properly
> >>>>> implement the get/set_config callbacks. Otherwise, receiving of the
> messages
> >>>>> will result in RTE_VHOST_MSG_RESULT_ERR and subsequent vhost
> >>>>> disconnection.
> >>>>> This looks strange, because supported protocol features normally enabled
> by
> >>>>> default. Am I misunderstood something ?
> >>>> QEMU will not send the messages if VHOST_USER_PROTOCOL_F_CONFIG
> >>> wasn't enabled.
> >>>
> >>> So, you're going to enable it only by explicit call to
> >>> 'rte_vhost_driver_set_features' ?
> >>>
> >>> In this case I'm assuming that you're implementing your own vhost backend.
> >>> But why you're not using 'dev->extern_ops' and corresponding
> 'pre_msg_handle'
> >>> or 'post_msg_handle' to handle your GET/SET_CONFIG messages like it does
> >>> 'vhost_crypto' backend ?
> >> The patch was developed one year ago, while DPDK didn't have external ops.
> >
> > So, maybe it's time to reconsider the implementation.
> 
> +1
Okay, I will only add related messages definition in this patch and remove the
Callbacks.
> 
> >> The get_config/set_config was defined for all the virtio devices, so I think it
> makes
> >> more sense adding here.
> >
> > VHOST_USER_*_CRYPTO_SESSION messages are defined for all the virtio
> devices
> > too, however they makes sense for vhost_crypto backend only. These
> messages
> > (GET/SET_CONFIG) makes sense only when callbacks (get/set_config) are
> > implemented, so IMHO it's better to implement their handlers along with the
> > callbacks, i.e. inside the implementation of your vhost backend.
> >
> > Maxime, Tiwei, what do you think ?
> 
> I would prefer it to be implemented in SPDK directly as a pre_handler
> callback, as I don't foresee a need for it for other backends, and it
> would avoid breaking the API.
> 
> It would imply fixing the beginning of vhost_user_msg_handler() to
> accept requests > VHOST_USER_MAX and add necessary check before doing
> the debug logs.
> 
> With above change we would also be able to remove VHOST_CRYPTO requests
> from vhost_user.c, and we could then work on moving vhost-net bits
> out of this file too.
> 
> Regards,
> Maxime