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Message-ID: <4d3ea715-676c-c550-cff6-18c94a9d93e6@gmail.com> Date: Fri, 3 May 2019 19:04:35 -0700 From: Florian Fainelli <f.fainelli@...il.com> To: Vladimir Oltean <olteanv@...il.com>, vivien.didelot@...il.com, andrew@...n.ch, davem@...emloft.net Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH net-next 4/9] net: dsa: Keep private info in the skb->cb On 5/3/2019 6:18 PM, Vladimir Oltean wrote: > Map a DSA structure over the 48-byte control block that will hold > persistent skb info on transmit and receive. > On receive you cannot quite do that because you don't know if the DSA master network device calls netif_receive_skb() or napi_gro_receive(). The latter arguably may not be able to aggregate flows at all because it does not know how to parse the SKB, but the point remains that skb->cb[] on receive may already be used, up to 48 bytes already. I tried to make use of it for storing the HW extracted Broadcom tag, but it blew the budge on 64-bit hosts: https://www.spinics.net/lists/netdev/msg337777.html Not asking you to change anything here, just to be aware of it. > Also add a DSA_SKB_CB_PRIV() macro which retrieves a pointer to the > space up to 48 bytes that the DSA structure does not use. This space can > be used for drivers to add their own private info. > > One use is for the PTP timestamping code path. When cloning a skb, > annotate the original with a pointer to the clone, which the driver can > then find easily and place the timestamp to. This avoids the need of a > separate queue to hold clones and a way to match an original to a cloned > skb. > > Signed-off-by: Vladimir Oltean <olteanv@...il.com> Reviewed-by: Florian Fainelli <f.fainelli@...il.com> -- Florian
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