netdev - Re: [PATCH v2 1/2] net: dsa: ensure linearized SKBs in case of tail taggers

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Message-ID: <20210723122213.fvhudwyk36u7pw52@skbuf>
Date:   Fri, 23 Jul 2021 15:22:13 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com,
        vivien.didelot@...il.com, davem@...emloft.net, kuba@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] net: dsa: ensure linearized SKBs in case of tail
 taggers

On Fri, Jul 23, 2021 at 09:47:39AM +0200, Lino Sanfilippo wrote:
> since I got a message that the patches have already been applied to netdev/net.git.
> How should I proceed if I want to send a new version of the series? Just ignore the
> merge to netdev and send the patches nevertheless?

Since the git history is immutable you need to work with what is already
in the current net/master branch. What do you want to change, just
address the feedback I gave? If that is all, just don't bother, I intend
to look at adding a framework through which the DSA master can declare
what features it supports in conjunction with specific DSA tagging protocols.
That is material for net-next, and Dave took your patch at the last
minute for the "net" pull request towards Linus' tree. If you send
another patch on "net" in that area now, we'd have to wait for another
week or two until "net" will be merged again into "net-next". Not sure
if it's worth it. The only thing that was of concern to me is that you
assign the DSA interface's slave->vlan_features = master->vlan_features.
So even though you clear the NETIF_F_SG feature for the DSA slave
interface, VLAN uppers on top of DSA interfaces will still have NETIF_F_SG.
However, those skbs will be linearized during the dev_queue_xmit call
done by the 8021q driver towards DSA, so in the end, the way in which
you restructured the code may not be cosmetically ideal, but also
appears to not be functionally problematic.
Anyway, your patch will probably conflict with the stable trees (the
tag_ops->needed_tailroom was introduced very recently), so we will have
another chance to fix it up when Greg sends the email that the patch
failed to apply.