Subject: Re: [PATCH] tun: support not enabling carrier in TUNSETIFF

From: Stephen Hemminger <[email-masked]>
Date: Mon, 19 Sep 2022 10:18:02 -0700

On Fri, 16 Sep 2022 16:45:52 -0700
Patrick Rohr <[email-masked]> wrote:

> diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
> index 2ec07de1d73b..12dde91957a5 100644
> --- a/include/uapi/linux/if_tun.h
> +++ b/include/uapi/linux/if_tun.h
> @@ -75,6 +75,8 @@
>  #define IFF_MULTI_QUEUE 0x0100
>  #define IFF_ATTACH_QUEUE 0x0200
>  #define IFF_DETACH_QUEUE 0x0400
> +/* Used in TUNSETIFF to bring up tun/tap without carrier */
> +#define IFF_NO_CARRIER IFF_DETACH_QUEUE

Overloading a flag in existing user API is likely to break
some application somewhere...