Interface auto-cloning bug or feature?

[Maksim Yevmenkin]

On 9/23/08, Kostik Belousov <kostikbel at gmail.com> wrote:

[...]

>  > attached is a slightly better patch for tap(4). the idea is to use
>  > extra ALLOCATED flag that prevents the race Kostik pointed out. could
>  > you please give it a try? any review comments are greatly appreciated.
>  > if this is acceptable, i will prepare something similar for tun(4)
>
> The tap should use make_dev_credf(MAKEDEV_REF) instead of
>  make_dev/dev_ref sequence in the clone handler. For similar reasons, I
>  think it is slightly better to do a dev_ref() immediately after setting
>  the TAP_ALLOCATED flag without dropping tapmtx.

could you please explain why it is better?

>  I cannot figure out how tap_clone_create/tap_clone_destroy are being
>  called. Can it be garbage-collected ?

ah, this is interface clone feature, i.e. one can do 'ifconfig tap0
create/destroy' to create an interface and device node. take a look at
IFC_SIMPLE_DECLARE() macro.

>  The whole module unload sequence looks unsafe.

yes, it is unsafe. it even has comment about it :) i guess, i could
fix it too while i'm at it :)

thanks,
max