netdev - Re: [PATCH net] qmi_wwan: Clone the skb when in pass-through mode

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Date:   Tue, 15 Jun 2021 12:51:46 +0200
From:   Kristian Evensen <kristian.evensen@...il.com>
To:     Bjørn Mork <bjorn@...k.no>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        subashab@...eaurora.org
Subject: Re: [PATCH net] qmi_wwan: Clone the skb when in pass-through mode

Hi Bjørn,

On Tue, Jun 15, 2021 at 12:04 PM Bjørn Mork <bjorn@...k.no> wrote:
> Yes, FLAG_MULTI_PACKET is only applicable to the qmimux case. But I
> think Jakub is right that we should set it anyway. There is no way to
> return from rx_fixup without an error or further processing of the skb,
> unless we set FLAG_MULTI_PACKET.  Or invent something else.  But setting
> that flag and then add the necessary usnet_sb_return call doesn't look
> too bad?

Just so that I am sure that we are on the same page. What you are
suggesting is something like:

* Update FLAG_MULTI_PACKET when qmimux is set/unset.
* Replace the call to netif_rx() inside qmimux_rx_fixup() with a call
to usbnet_skb_return.
* I guess we need to keep the code that updates the qmimux interface
counters. I guess we can just call this code unconditionally?

I think this would be a really nice solution. The same (at least
FLAG_MULTI_PACKET + usbnet_skb_return) could be applied to pass
through as well, giving us consistent handling of aggregated packets.
While we might not save a huge number of lines, I believe the
resulting code will be easier to understand.

If we agree that this is a good way forward, I can prepare a patch. I
have everything set up and ready to go.

Kristian