netdev - Re: [PATCH net-next 06/13] net: original ingress device index in PKTINFO

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Date:	Thu, 5 May 2016 11:41:27 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	David Ahern <dsa@...ulusnetworks.com>
cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 06/13] net: original ingress device index in
 PKTINFO


	Hello,

On Wed, 4 May 2016, David Ahern wrote:

> Applications such as OSPF and BFD need the original ingress device not
> the VRF device; the latter can be derived from the former. To that end
> add the skb_iif to inet_skb_parm and set it in ipv4 code after clearing
> the skb control buffer similar to IPv6. From there the pktinfo can just
> pull it from cb with the PKTINFO_SKB_CB cast.
> 
> The previous patch moving the skb->dev change to L3 means nothing else
> is needed for IPv6; it just works.
> 
> Signed-off-by: David Ahern <dsa@...ulusnetworks.com>
> ---
>  include/net/ip.h       | 1 +
>  net/ipv4/ip_input.c    | 1 +
>  net/ipv4/ip_sockglue.c | 9 +++++++--
>  3 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/include/net/ip.h b/include/net/ip.h
> index 247ac82e9cf2..37165fba3741 100644
> --- a/include/net/ip.h
> +++ b/include/net/ip.h
> @@ -36,6 +36,7 @@
>  struct sock;
>  
>  struct inet_skb_parm {
> +	int			iif;
>  	struct ip_options	opt;		/* Compiled IP options		*/
>  	unsigned char		flags;
>  
> diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
> index 37375eedeef9..4b351af3e67b 100644
> --- a/net/ipv4/ip_input.c
> +++ b/net/ipv4/ip_input.c
> @@ -478,6 +478,7 @@ int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt,
>  
>  	/* Remove any debris in the socket control block */
>  	memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
> +	IPCB(skb)->iif = skb->skb_iif;

	For loopback traffic (including looped back multicast)
this is now a zero :( Can inet_iif be moved to ip_rcv_finish
instead? Still, we spend cycles in fast path in case nobody
listens for such info.

>  	/* Must drop socket now because of tproxy. */
>  	skb_orphan(skb);
> diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
> index bdb222c0c6a2..dbcd027c38e7 100644
> --- a/net/ipv4/ip_sockglue.c
> +++ b/net/ipv4/ip_sockglue.c
> @@ -476,9 +476,9 @@ static bool ipv4_datagram_support_cmsg(const struct sock *sk,
>  	    (!skb->dev))
>  		return false;
>  
> +	/* see comment in ipv4_pktinfo_prepare about CB re-use */
>  	info = PKTINFO_SKB_CB(skb);
>  	info->ipi_spec_dst.s_addr = ip_hdr(skb)->saddr;
> -	info->ipi_ifindex = skb->dev->ifindex;

	This code is only for SOF_TIMESTAMPING_OPT_CMSG.
I'm not sure skb passes ip_rcv in all cases. So, we can not
easily remove it.

Regards

--
Julian Anastasov <ja@....bg>