On Tue, Aug 10, 2021 at 06:04:50PM +0200, Pali Rohár wrote: > On Tuesday 10 August 2021 17:39:41 Guillaume Nault wrote: > > On Mon, Aug 09, 2021 at 09:31:09PM +0200, Pali Rohár wrote: > > > Better to wait. I would like hear some comments / review on this patch > > > if this is the correct approach as it adds a new API/ABI for userspace. > > > > Personally I don't understand the use case for setting the ppp unit at > > creation time. > > I know about two use cases: > > * ppp unit id is used for generating network interface name. So if you > want interface name ppp10 then you request for unit id 10. It is > somehow common that when ppp interface has prefix "ppp" in its name > then it is followed by unit id. Seems that existing ppp applications > which use "ppp<num>" naming expects this. But of course you do not > have to use this convention and rename interfaces as you want. Really, with the netlink API, the interface name has to be set with IFLA_IFNAME. There's no point in adding a new attribute just to have a side effect on the device name. > * Some of ppp ioctls use unit id. So you may want to use some specific > number for some network interface. So e.g. unit id 1 will be always > for /dev/ttyUSB1. But what's the point of forcing unit id 1 for a particular interface? One can easily get the assigned unit id with ioctl(PPPIOCGUNIT). > > I didn't implement it on purpose when creating the > > netlink interface, as I didn't have any use case. > > > > On the other hand, adding the ppp unit in the netlink dump is probably > > useful. > > Yes, this could be really useful as currently if you ask netlink to > create a new ppp interface you have to use ioctl to retrieve this unit > id. But ppp currently does not provide netlink dump operation. > > Also it could be useful for this "bug": > https://lore.kernel.org/netdev/20210807132703.26303-1-pali@xxxxxxxxxx/t/#u This patch itself makes sense, but how is that related to unit id? > And with unit id there also another issue: > https://lore.kernel.org/netdev/20210807160050.17687-1-pali@xxxxxxxxxx/t/#u This patch shows why linking unit id and interface name are a bad idea. Instead of adding more complexity with unit id, I'd prefer to have a new netlink attribute that says "don't generate the interface name based on the unit id". That's how the original implementation worked by the way and I'm really sad I accepted to change it... > But due to how it is used we probably have to deal with it how ppp unit > id are defined and assigned... >
