On Tue, Sep 19, 2017 at 2:02 PM, Jason A. Donenfeld <ja...@zx2c4.com> wrote: > On Tue, Sep 19, 2017 at 10:40 PM, Cong Wang <xiyou.wangc...@gmail.com> wrote: >> By "notification" I assume you mean netlink notification. > > Yes, netlink notification. > >> The question is why does the process in A still care about >> the device sitting in B? >> >> Also, the process should be able to receive a last notification >> on IFF_UP|IFF_RUNNING before device is finally moved to B. >> After this point, it should not have any relation to netns A >> any more, like the device were completely gone. > > That's very clearly not the case with a tun device. Tun devices work > by letting a userspace process control the inputs (ndo_start_xmit) and > outputs (netif_rx) of the actual network device. This controlling > userspace process needs to know when its own interface that it > controls goes up and down. In the kernel, we can do this by just > checking dev->flags&IFF_UP, and receive notifications on ndo_open and > ndo_stop. In userspace, the controlling process looses the ability to > receive notifications like ndo_open/ndo_stop when the interface is > moved to a new namespace. After the interface is moved to a namespace, > the process will still control inputs and ouputs (ndo_start_xmit and > netif_rx), but it will no longer receive netlink notifications for the > equivalent of ndo_open and ndo_stop. This is problematic.
Sounds like we should set NETIF_F_NETNS_LOCAL for tun device. What is your legitimate use case of send/receive packet to/from a tun device in a different netns?
