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Date:   Mon, 19 Sep 2022 10:18:02 -0700
From:   Stephen Hemminger <stephen@networkplumber.org>
To:     Patrick Rohr <prohr@google.com>
Cc:     "David S . Miller" <davem@davemloft.net>,
        Linux Network Development Mailing List 
        <netdev@vger.kernel.org>,
        "Maciej =?UTF-8?B?xbtlbmN6eWtvd3Nr?= =?UTF-8?B?aQ==?=" 
        <maze@google.com>, Lorenzo Colitti <lorenzo@google.com>,
        Jason Wang <jasowang@redhat.com>
Subject: Re: [PATCH] tun: support not enabling carrier in TUNSETIFF
Message-ID: <20220919101802.4f4d1a86@hermes.local>
In-Reply-To: <20220916234552.3388360-1-prohr@google.com>
References: <20220916234552.3388360-1-prohr@google.com>
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On Fri, 16 Sep 2022 16:45:52 -0700
Patrick Rohr <prohr@google.com> 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...