netdev - Re: [PATCH net-next v5 07/11] tcp: coalesce/collapse must respect MPTCP extensions

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Message-ID: <90c0c531-45e4-4937-552a-898aff733756@gmail.com>
Date:   Fri, 20 Dec 2019 07:25:45 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        netdev@...r.kernel.org, mptcp@...ts.01.org
Cc:     Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v5 07/11] tcp: coalesce/collapse must respect
 MPTCP extensions



On 12/19/19 2:34 PM, Mat Martineau wrote:
> Coalesce and collapse of packets carrying MPTCP extensions is allowed
> when the newer packet has no extension or the extensions carried by both
> packets are equal.
> 
> This allows merging of TSO packet trains and even cross-TSO packets, and
> does not require any additional action when moving data into existing
> SKBs.
> 
> v3 -> v4:
>  - allow collapsing, under mptcp_skb_can_collapse() constraint
> 
> Co-developed-by: Paolo Abeni <pabeni@...hat.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> Signed-off-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>
> ---
>  include/net/mptcp.h   | 54 +++++++++++++++++++++++++++++++++++++++++++
>  include/net/tcp.h     |  8 +++++++
>  net/ipv4/tcp_input.c  | 11 ++++++---
>  net/ipv4/tcp_output.c |  2 +-
>  4 files changed, 71 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> index f9f668ac4339..8e27e33861ab 100644
> --- a/include/net/mptcp.h
> +++ b/include/net/mptcp.h
> @@ -8,6 +8,7 @@
>  #ifndef __NET_MPTCP_H
>  #define __NET_MPTCP_H
>  
> +#include <linux/skbuff.h>
>  #include <linux/types.h>
>  
>  /* MPTCP sk_buff extension data */
> @@ -24,4 +25,57 @@ struct mptcp_ext {
>  			__unused:2;
>  };
>  
> +#ifdef CONFIG_MPTCP
> +
> +/* move the skb extension owership, with the assumption that 'to' is
> + * newly allocated
> + */
> +static inline void mptcp_skb_ext_move(struct sk_buff *to,
> +				      struct sk_buff *from)
> +{
> +	if (!skb_ext_exist(from, SKB_EXT_MPTCP))
> +		return;
> +
> +	if (WARN_ON_ONCE(to->active_extensions))
> +		skb_ext_put(to);
> +
> +	to->active_extensions = from->active_extensions;
> +	to->extensions = from->extensions;
> +	from->active_extensions = 0;
> +}
> +
> +static inline bool mptcp_ext_matches(const struct mptcp_ext *to_ext,
> +				     const struct mptcp_ext *from_ext)
> +{
> +	return !from_ext ||
> +	       (to_ext && from_ext &&
> +	        !memcmp(from_ext, to_ext, sizeof(struct mptcp_ext)));

There is a hole at the end of struct mptcp_ext

How is it properly cleared/initialized so that the memcmp() wont
spuriously fail ?

Thanks.