> From: Jason Wang <jasowang@xxxxxxxxxx> > Sent: Friday, June 25, 2021 8:59 AM > > 在 2021/6/24 下午3:59, Parav Pandit 写道: > > > >> From: Jason Wang <jasowang@xxxxxxxxxx> > >> 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. > > > I don't see why it needs typecast, virtio_net_config is also uABI, you can > deference the fields directly. > User wants set only the mac address of the config space. How do user space tell this? Pass the whole virtio_net_config and inform via side channel? Or vendor driver is expected to compare what fields changed from old config space? > > > > >> 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. > > > This is something we need to fix I think. Or if it's really useful to > allowing the attributes to be modified after the device is created. > > Why not simply allow the config to be built only at device creation? > That avoids the problem of modifying fields after bind to vhost. But UAPI issue still remains so lets resolve that first. > > > > >>>>>> 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. > > > No, a single skb not single nla_put(). > > Actually git grep told me a very good example of carrying uABI via > netlink, that is the ndt_config: > > 1) we had ndt_config definition in the uAPI > 2) netlink simply carries the structure in neightbl_fill_info(): > > if (nla_put(skb, NDTA_CONFIG, sizeof(ndc), &ndc)) > Sure. But the reverse path doesn’t have this that requires side band mask. My concern is not for existing virtio_net_config layout, but the future increase of it requires size based typecasting on both directions. > > For virito_net_config, why not simply: > > len = ops->get_config_len(); > config = kmalloc(len, GFP_KERNEL); > ops->get_config(vdev, 0, config, len); > nla_put(skb, VIRTIO_CONFIG, config, len); User space need to parse content based on this length as it can change in future. Length telling how to typecast is want I want to avoid here. > nla_put_le64(skb, VIRTIO_FETURES, features); > > For build_config, we can simply do thing reversely. Then everything > works via the existing virtio uAPI/ABI. > In reverse path how do you tell which fields of the config space to set and which to ignore? Shall we use u64 features for it? Will type of device able to describe their config space via a feature bit? > > > > >>>> 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. > > > Well, it doesn't do anything difference compared to xxx_is_valid which > just calculating the offset implicitly (via the compiler). > > > > 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(). > > > The points are: > > 1) Avoid duplicating the existing uAPIs > 2) Avoid unnecessary parsing in the netlink, netlink is just the > transport, it's the charge of the vDPA parent to do that > All those parsing will move to vendor drivers to validate offset/length to update only specific fields of config space. It is a transport to carry fields which is what we are using for. I agree there that these config fields are exposed individually in both directions to keep it safe from structure layout increments. > Thanks > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
