On Thu, 2 Jun 2022 11:19:29 +0300 Kaarel Pärtel wrote: > The idea here is simple. The vcan and the dummy network devices > currently do not set the operational state of the interface. > The result is that the interface state will be UNKNOWN. > > The kernel considers the unknown state to be the same as up: > https://elixir.bootlin.com/linux/latest/source/include/linux/netdevice.h#L4125 > > However for users this creates confusion: > https://serverfault.com/questions/629676/dummy-network-interface-in-linux > > The change in this patch is very simple. When the interface is set up, the > operational state is set to IF_OPER_UP. > > Signed-off-by: Kaarel Pärtel <kaarelp2rtel@xxxxxxxxx> You can change the carrier state from user space on a dummy device, that will inform the kernel of the operstate: # ip link add type dummy # ip link show dev dummy0 8: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000 link/ether 8e:35:15:22:e3:d7 brd ff:ff:ff:ff:ff:ff # ip link set dev dummy0 up # ip link show dev dummy0 8: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000 link/ether 8e:35:15:22:e3:d7 brd ff:ff:ff:ff:ff:ff # ip link set dev dummy0 carrier off # ip link set dev dummy0 carrier on # ip link show dev dummy0 8: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000 link/ether 8e:35:15:22:e3:d7 brd ff:ff:ff:ff:ff:ff Flipping all soft devices which don't have a lower or don't expect user space management to UP is fine but doing it one by one feels icky. Yet another random thing a driver author has to know to flip. If people are confused about seeing UNKNOWN in ip link output maybe we should move displaying that under the -d flag (detailed output)? Saves space, and nobody will get confused.
