Jason Wang
2021-Jun-24 07:05 UTC
[PATCH linux-next v3 2/6] vdpa: Introduce query of device config layout
? 2021/6/24 ??2:29, Parav Pandit ??:> >> From: Jason Wang <jasowang at redhat.com> >> Sent: Thursday, June 24, 2021 11:13 AM >> >> ? 2021/6/23 ??12:22, Parav Pandit ??: >>>> From: Jason Wang <jasowang at redhat.com> >>>> Sent: Wednesday, June 23, 2021 9:39 AM >>>> >>>> ? 2021/6/22 ??10:03, Parav Pandit ??: >>>>>> Is it better to use a separate enum for net specific attributes? >>>>>> >>>>> Yes, because they are only net specific. >>>>> I guess it is related to your below question. >>>>> >>>>>> Another question (sorry if it has been asked before). Can we simply >>>>>> return the config (binary) to the userspace, then usespace can use >>>>>> the existing uAPI like virtio_net_config plus the feature to >>>>>> explain the >>>> config? >>>>> We did discuss in v2. >>>>> Usually returning the whole blob and parsing is not desired via netlink. >>>>> Returning individual fields give the full flexibility to return only >>>>> the valid >>>> fields. >>>>> Otherwise we need to implement another bitmask too to tell which >>>>> fields >>>> from the struct are valid and share with user space. >>>>> Returning individual fields is the widely used approach. >>>> The main concerns are: >>>> >>>> 1) The blob will be self contained if it was passed with the >>>> negotiated features, so we don't need bitmask. >>> Which fields of the struct are valid is told by additional fields. >>>> 2) Using individual fields means it must duplicate the config fields >>>> of every virtio devices >>>> >>> Mostly no. if there are common config fields across two device types, >>> they would be named as >>> VDPA_ATTR_DEV_CFG_* >>> Net specific will be, >>> VDPA_ATTR_DEV_NET_CFG_* >>> Block specific, will be, >>> VDPA_ATTR_DEV_BLK_CFG_* >> >> I meant it looks like VDPA_ATTR_DEV_NET will duplicate all the fields of: >> >> struct virtio_net_config; >> >> And VDPA_ATTR_DEV_BLOCK will duplicate all the fields of >> >> struct virtio_blk_config; which has ~21 fields. >> >> And we had a plenty of other types of virtio devices. >> >> Consider we had a mature set of virtio specific uAPI for config space. >> It would be a burden if we need an unnecessary translation layer of netlink in >> the middle: >> >> [vDPA parent (virtio_net_config)] <-> [netlink (VDPA_ATTR_DEV_NET_XX)] >> <-> [userspace (VDPA_ATTR_DEV_NET_XX)] >>> <-> [ user (virtio_net_config)] > This translation is not there. We show relevant net config fields as VDPA_ATTR_DEV_NET individually. > It is not a binary dump which is harder for users to parse and make any use of it.The is done implicitly, user needs to understand the semantic of virtio_net_config and map the individual fields to the vdpa tool sub-command.> > It is only one level of translation from virtio_net_config (kernel) -> netlink vdpa fields. > It is similar to 'struct netdevice' -> rtnl info fields.I think not, the problem is that the netdevice is not a part of uAPI but virtio_net_config is.> >> If we make netlink simply a transport, it would be much easier. And we had >> the chance to unify the logic of build_config() and set_config() in the driver. > How? We need bit mask to tell that out of 21 fields which fields to update and which not. > And that is further mixed with offset and length.So set_config() could be called from userspace, so did build_config(). The only difference is: 1) they're using different transport, ioctl vs netlink 2) build_config() is only expected to be called by the management tool If qemu works well via set_config ioctl, netlink should work as well. Btw, what happens if management tool tries to modify the mac of vDPA when the device is already used by the driver?> >> >>>> And actually, it's not the binary blob since uapi clearly define the >>>> format (e.g struct virtio_net_config), can we find a way to use that? >>>> E.g introduce device/net specific command and passing the blob with >>>> length and negotiated features. >>> Length may change in future, mostly expand. And parsing based on length >> is not such a clean way. >> >> >> Length is only for legal checking. The config is self contained with: >> > Unlikely. When structure size increases later, the parsing will change based on the length. > Because older kernel would return shorter length with older iproute2 tool.This is fine since the older kernel only support less features. The only possible issue if the old iproute 2 runs on new kernel. With the current proposal, it may cause some config fields can't not be showed. I think it might be useful to introduce a command to simply dump the config space.> So user space always have to deal and have nasty parsing/typecasting based on the length.That's how userspace (Qemu) is expected to work now. The userspace should determine the semantic of the fields based on the features. Differentiate config fields doesn't help much, e.g userspace still need to differ LINK_UP and ANNOUNCE for the status field.> >> 1) device id >> 2) features >> >> >>> Parsing fields require knowledge of features as well and application needs >> to make multiple netlink calls to parse the config space. >> >> >> I think we don't care about the performance in this case. It's about three >> netlink calls: >> > Its not about performance. By the time 1st call is made, features got updated and it is out of sync with config. > >> 1) get config >> 2) get device id >> 3) get features >> > This requires using features from 3rd netlink output to decode output of 1st netlink output. > Which is a bit odd of netlink. > Other netlink nla_put() probably sending whole structure doesn?t need to do it.Well, we can pack them all into a single skb isn't it? (probably with a config len).> >> For build config, it's only one >> >> 1) build config >> >> >>> I prefer to follow rest of the kernel style to return self contained >> invidividual fields. >> >> >> But I saw a lot of kernel codes choose to use e.g nla_put() directly with >> module specific structure. >> > It might be self-contained structure that probably has not found the need to expand.I think it's just a matter of putting the config length with the config data. Note that we've already had .get_config_size() ops for validating inputs through VHOST_SET_CONFIG/VHOST_GET_CONFIG. Thanks
Parav Pandit
2021-Jun-24 07:59 UTC
[PATCH linux-next v3 2/6] vdpa: Introduce query of device config layout
> From: Jason Wang <jasowang at redhat.com> > Sent: Thursday, June 24, 2021 12:35 PM > > >> Consider we had a mature set of virtio specific uAPI for config space. > >> It would be a burden if we need an unnecessary translation layer of > >> netlink in the middle: > >> > >> [vDPA parent (virtio_net_config)] <-> [netlink > >> (VDPA_ATTR_DEV_NET_XX)] <-> [userspace > (VDPA_ATTR_DEV_NET_XX)] > >>> <-> [ user (virtio_net_config)] > > This translation is not there. We show relevant net config fields as > VDPA_ATTR_DEV_NET individually. > > It is not a binary dump which is harder for users to parse and make any use > of it. > > > The is done implicitly, user needs to understand the semantic of > virtio_net_config and map the individual fields to the vdpa tool sub- > command.Mostly not virtio_net_config is for the producer and consumer sw entities. Here user doesn't know about such layout and where its located. User only sets config params that gets set in the config space. (without understanding what is config layout and its location).> > > > > > It is only one level of translation from virtio_net_config (kernel) -> netlink > vdpa fields. > > It is similar to 'struct netdevice' -> rtnl info fields. > > > I think not, the problem is that the netdevice is not a part of uAPI but > virtio_net_config is.Virtio_net_config is a UAPI for sw consumption. That way yes, netlink can also do it, however it requires side channel communicate what is valid.> > > > > >> If we make netlink simply a transport, it would be much easier. And we > had > >> the chance to unify the logic of build_config() and set_config() in the > driver. > > How? We need bit mask to tell that out of 21 fields which fields to update > and which not. > > And that is further mixed with offset and length. > > > So set_config() could be called from userspace, so did build_config(). > The only difference is: > > 1) they're using different transport, ioctl vs netlink > 2) build_config() is only expected to be called by the management tool > > If qemu works well via set_config ioctl, netlink should work as well. >mlx5 set_config is noop. vdpa_set_config() need to return an error code. I don't vp_vdpa.c blindly writes the config as its passthrough. Parsing which fields to write and which not, using offset and length is a messy code with typecast and compare old values etc.> Btw, what happens if management tool tries to modify the mac of vDPA > when the device is already used by the driver?At present it allows modifying, but it should be improved in future to fail if device is in use.> >>>> And actually, it's not the binary blob since uapi clearly define the > >>>> format (e.g struct virtio_net_config), can we find a way to use that? > >>>> E.g introduce device/net specific command and passing the blob with > >>>> length and negotiated features. > >>> Length may change in future, mostly expand. And parsing based on > length > >> is not such a clean way. > >> > >> > >> Length is only for legal checking. The config is self contained with: > >> > > Unlikely. When structure size increases later, the parsing will change based > on the length. > > Because older kernel would return shorter length with older iproute2 tool. > > > This is fine since the older kernel only support less features. The only > possible issue if the old iproute 2 runs on new kernel. With the current > proposal, it may cause some config fields can't not be showed. >Not showing is ok. But the code is messy to typecast on size.> I think it might be useful to introduce a command to simply dump the > config space. > > > > So user space always have to deal and have nasty parsing/typecasting > based on the length.Such nasty parsing is not required for netlink interface.> > > That's how userspace (Qemu) is expected to work now. The userspace > should determine the semantic of the fields based on the features. > > Differentiate config fields doesn't help much, e.g userspace still need > to differ LINK_UP and ANNOUNCE for the status field.Yes, this parsing is from constant size u16 status.> >[..]> > > Its not about performance. By the time 1st call is made, features got > updated and it is out of sync with config. > > > >> 1) get config > >> 2) get device id > >> 3) get features > >> > > This requires using features from 3rd netlink output to decode output of > 1st netlink output. > > Which is a bit odd of netlink. > > Other netlink nla_put() probably sending whole structure doesn?t need to > do it. > > > Well, we can pack them all into a single skb isn't it? (probably with a > config len). >You want to pack features and config both in the single nla_put()? If so, it isn't necessary. There are more examples in kernel that adds individual fields instead of nla_put(blob). I wouldn?t follow those nla_put() callers.> > > > >> For build config, it's only one > >> > >> 1) build config > >> > >> > >>> I prefer to follow rest of the kernel style to return self contained > >> invidividual fields. > >> > >> > >> But I saw a lot of kernel codes choose to use e.g nla_put() directly with > >> module specific structure. > >> > > It might be self-contained structure that probably has not found the need > to expand. > > > I think it's just a matter of putting the config length with the config > data. Note that we've already had .get_config_size() ops for validating > inputs through VHOST_SET_CONFIG/VHOST_GET_CONFIG.This length comes as part of the netlink interface already, no need for extra length. The whole point is to avoid parsing based on length. We cannot change the virtio_net_config UAPI in use, but netlink code doesn?t need to be bound to size based typecasting and compare fields during build_config().