netdev - Re: [PATCH net] net: accept UFO datagrams from tuntap and packet

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Message-Id: <20171118.104243.1900474824000692140.davem@davemloft.net>
Date:   Sat, 18 Nov 2017 10:42:43 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     willemdebruijn.kernel@...il.com
Cc:     netdev@...r.kernel.org, jasowang@...hat.com, mkubecek@...e.cz,
        willemb@...gle.com
Subject: Re: [PATCH net] net: accept UFO datagrams from tuntap and packet

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Fri, 17 Nov 2017 17:59:13 -0500

> Tuntap and similar devices can inject GSO packets. Accept type
> VIRTIO_NET_HDR_GSO_UDP, even though not generating UFO natively.
> 
> Processes are expected to use feature negotiation such as TUNSETOFFLOAD
> to detect supported offload types and refrain from injecting other
> packets. This process breaks down with live migration: guest kernels
> do not renegotiate flags, so destination hosts need to expose all
> features that the source host does.
> 
> Partially revert the UFO removal from 182e0b6b5846~1..d9d30adf5677.
> This patch introduces nearly(*) no new code to simplify verification.
> It brings back verbatim tuntap UFO negotiation, VIRTIO_NET_HDR_GSO_UDP
> insertion and software UFO segmentation.

This looks good, one minor nit:

> @@ -2369,6 +2369,10 @@ static int set_offload(struct tun_struct *tun, unsigned long arg)
>  				features |= NETIF_F_TSO6;
>  			arg &= ~(TUN_F_TSO4|TUN_F_TSO6);
>  		}
> +
> +		if (arg & TUN_F_UFO) {
> +			arg &= ~TUN_F_UFO;
> +		}

This can be just simply "arg &= ~TUN_F_UFO;"?  If anything the curly braces
should be removed for a single statement basic block.

Thanks for working so hard on fixing this.