netdev - Re: [PATCH v3 net-next 01/12] net: dsa: implement a central TX reallocation procedure

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Date:   Mon, 2 Nov 2020 12:43:55 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc:     andrew@...n.ch, vivien.didelot@...il.com, kuba@...nel.org,
        Christian Eggers <ceggers@...i.de>,
        Kurt Kanzenbach <kurt@...utronix.de>
Subject: Re: [PATCH v3 net-next 01/12] net: dsa: implement a central TX
 reallocation procedure



On 11/1/2020 11:16 AM, Vladimir Oltean wrote:
> At the moment, taggers are left with the task of ensuring that the skb
> headers are writable (which they aren't, if the frames were cloned for
> TX timestamping, for flooding by the bridge, etc), and that there is
> enough space in the skb data area for the DSA tag to be pushed.
> 
> Moreover, the life of tail taggers is even harder, because they need to
> ensure that short frames have enough padding, a problem that normal
> taggers don't have.
> 
> The principle of the DSA framework is that everything except for the
> most intimate hardware specifics (like in this case, the actual packing
> of the DSA tag bits) should be done inside the core, to avoid having
> code paths that are very rarely tested.
> 
> So provide a TX reallocation procedure that should cover the known needs
> of DSA today.
> 
> Note that this patch also gives the network stack a good hint about the
> headroom/tailroom it's going to need. Up till now it wasn't doing that.
> So the reallocation procedure should really be there only for the
> exceptional cases, and for cloned packets which need to be unshared.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> Tested-by: Christian Eggers <ceggers@...i.de> # For tail taggers only
> Tested-by: Kurt Kanzenbach <kurt@...utronix.de>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian