Hello Johannes, On Wed, Jun 2, 2021 at 10:38 AM Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote: >> Wow, this is a perfect solution! I just could not help but praise this >> proposal :) > > Heh. > >> When researching the latest WWAN device drivers and related >> discussions, I began to assume that implementing the netdev management >> API without the dummy (no-op) netdev is only possible using genetlink. >> But this usage of a regular device specified by its name as a parent >> for netdev creation is so natural and clear that I believe in RTNL >> again. >> >> Let me place my 2 cents. Maybe the parent device attribute should be >> made generic? E.g. call it IFLA_PARENT_DEV_NAME, with usage semantics >> similar to the IFLA_LINK attribute for VLAN interfaces. The case when >> a user needs to create a netdev on behalf of a regular device is not >> WWAN specific, IMHO. So, other drivers could benefit from such >> attribute too. To be honest, I can not recall any driver that could >> immediately start using such attribute, but the situation with the >> need for such attribute seems to be quite common. > > That's a good question/thought. > > I mean, in principle this is trivial, right? Just add a > IFLA_PARENT_DEV_NAME like you say, and use it instead of > IFLA_WWAN_DEV_NAME. > > It'd come out of tb[] instead of data[] and in this case would remove > the need to add the additional data[] argument to rtnl_create_link() in > my patch, since it's in tb[] then. Yep, exactly. > The only thing I'd be worried about is that different implementations > use it for different meanings, but I guess that's not that big a deal? The spectrum of sane use of the IFLA_PARENT_DEV_NAME attribute by various subsystems and (or) drivers will be quite narrow. It should do exactly what its name says - identify a parent device. We can not handle the attribute in the common rtnetlink code since rtnetlink does not know the HW configuration details. That is why IFLA_PARENT_DEV_NAME should be handled by the RTNL ->newlink() callback. But after all the processing, the device that is identified by the IFLA_PARENT_DEV_NAME attribute should appear in the netdev->dev.parent field with help of SET_NETDEV_DEV(). Eventually RTNL will be able to fill IFLA_PARENT_DEV_NAME during the netdevs dump on its own, taking data from netdev->dev.parent. I assume that IFLA_PARENT_DEV_NAME could replace the IFLA_LINK attribute usage in such drivers as MBIM and RMNET. But the best way to evolve these drivers is to make them WWAN-subsystem-aware using the WWAN interface configuration API from your proposal, IMHO. -- Sergey
