linux-kernel - Re: [PATCH 5.10 113/290] net: dsa: implement a central TX reallocation procedure

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Message-ID: <20210315195601.auhfy5uafjafgczs@skbuf>
Date:   Mon, 15 Mar 2021 19:56:02 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>,
        Christian Eggers <ceggers@...i.de>
Subject: Re: [PATCH 5.10 113/290] net: dsa: implement a central TX
 reallocation procedure

+Andrew, Vivien,

On Mon, Mar 15, 2021 at 02:53:26PM +0100, gregkh@...uxfoundation.org wrote:
> From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>
> From: Vladimir Oltean <vladimir.oltean@....com>
>
> [ Upstream commit a3b0b6479700a5b0af2c631cb2ec0fb7a0d978f2 ]
>
> 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>
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---

For context, Sasha explains here:
https://www.spinics.net/lists/stable-commits/msg190151.html
(the conversation is somewhat truncated, unfortunately, because
stable-commits@...r.kernel.org ate my replies)
that 13 patches were backported to get the unrelated commit 9200f515c41f
("net: dsa: tag_mtk: fix 802.1ad VLAN egress") to apply cleanly with git-am.

I am not strictly against this, even though I would have liked to know
that the maintainers were explicitly informed about it.

Greg, could you make your stable backporting emails include the output
of ./get_maintainer.pl into the list of recipients? Thanks.