netdev - Re: [PATCH v1 net-next 3/6] net: add new control message for incoming HW-timestamped packets

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Date:   Wed, 26 Apr 2017 19:34:49 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Miroslav Lichvar <mlichvar@...hat.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Richard Cochran <richardcochran@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        "Keller, Jacob E" <jacob.e.keller@...el.com>,
        Denny Page <dennypage@...com>, Jiri Benc <jbenc@...hat.com>
Subject: Re: [PATCH v1 net-next 3/6] net: add new control message for incoming
 HW-timestamped packets

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 1b3317c..0a78f7f 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -160,6 +160,7 @@ static int netif_rx_internal(struct sk_buff *skb);
>  static int call_netdevice_notifiers_info(unsigned long val,
>                                          struct net_device *dev,
>                                          struct netdev_notifier_info *info);
> +static struct napi_struct *napi_by_id(unsigned int napi_id);
>
>  /*
>   * The @dev_base_head list is protected by @dev_base_lock and the rtnl
> @@ -863,6 +864,23 @@ struct net_device *dev_get_by_index(struct net *net, int ifindex)
>  }
>  EXPORT_SYMBOL(dev_get_by_index);
>
> +struct net_device *dev_get_by_napi_id(unsigned int napi_id)
> +{
> +       struct net_device *dev = NULL;
> +       struct napi_struct *napi;
> +
> +       rcu_read_lock();
> +
> +       napi = napi_by_id(napi_id);
> +       if (napi)
> +               dev = napi->dev;
> +
> +       rcu_read_unlock();
> +
> +       return dev;
> +}
> +EXPORT_SYMBOL(dev_get_by_napi_id);

Returning dev without holding a reference is not safe. You'll probably
have to call this with rcu_read_lock held instead.

Also, this generic napi function should probably be in a separate patch.

> diff --git a/net/socket.c b/net/socket.c
> index c2564eb..5ea5f29 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -662,6 +662,26 @@ static bool skb_is_err_queue(const struct sk_buff *skb)
>         return skb->pkt_type == PACKET_OUTGOING;
>  }
>
> +static void put_ts_pktinfo(struct msghdr *msg, struct sk_buff *skb)
> +{
> +#ifdef CONFIG_NET_RX_BUSY_POLL

Let's limit the ifdef scope to napi code. Perhaps we need an skb_get_napi_id
helper that returns 0 if the feature is not compiled in.

> +       struct scm_ts_pktinfo ts_pktinfo;
> +       struct net_device *orig_dev;
> +
> +       if (skb->napi_id < MIN_NAPI_ID || !skb_mac_header_was_set(skb))
> +               return;

This MIN_NAPI_ID check can be moved into dev_get_by_napi_id.

>  /*
>   * called from sock_recv_timestamp() if sock_flag(sk, SOCK_RCVTSTAMP)
>   */
> @@ -699,8 +719,12 @@ void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
>                 empty = 0;
>         if (shhwtstamps &&
>             (sk->sk_tsflags & SOF_TIMESTAMPING_RAW_HARDWARE) &&

This information is also informative with software timestamps.

And getting the real iif is definitely useful outside timestamps. An
alternative approach is to add versioning to IP_PKTINFO with a new
setsockopt IP_PKTINFO_VERSION plus a new struct in_pktinfo_v2
that extends in_pktinfo. Just a thought.