netdev - Re: [PATCH net-next] pppoe: new ioctl to extract per-channel stats

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Date:   Thu, 26 Mar 2020 11:42:19 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Simon Chopin <s.chopin@...halink.fr>
Cc:     Networking <netdev@...r.kernel.org>,
        Michal Ostrowski <mostrows@...thlink.net>,
        "David S . Miller" <davem@...emloft.net>,
        Guillaume Nault <gnault@...hat.com>
Subject: Re: [PATCH net-next] pppoe: new ioctl to extract per-channel stats

On Thu, Mar 26, 2020 at 11:32 AM Simon Chopin <s.chopin@...halink.fr> wrote:
>
> The PPP subsystem uses the abstractions of channels and units, the
> latter being an aggregate of the former, exported to userspace as a
> single network interface.  As such, it keeps traffic statistics at the
> unit level, but there are no statistics on the individual channels,
> partly because most PPP units only have one channel.
>
> However, it is sometimes useful to have statistics at the channel level,
> for instance to monitor multilink PPP connections. Such statistics
> already exist for PPPoL2TP via the PPPIOCGL2TPSTATS ioctl, this patch
> introduces a very similar mechanism for PPPoE via a new
> PPPIOCGPPPOESTATS ioctl.
>
> The contents of this patch were greatly inspired by the L2TP
> implementation, many thanks to its authors.

The patch looks fine from from an interface design perspective,
but I wonder if you could use a definition that matches the
structure layout and command number for PPPIOCGL2TPSTATS
exactly, rather than a "very similar mechanism" with a subset
of the fields. You would clearly have to pass down a number of
zero fields, but the implementation could be abstracted at a
higher level later.

      Arnd