netdev - Re: [PATCH 3/7] net/ethernet: Add parse_protocol header

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Date:   Thu, 24 Jan 2019 09:21:32 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jason Wang <jasowang@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [PATCH 3/7] net/ethernet: Add parse_protocol header_ops support

On Thu, Jan 24, 2019 at 4:48 AM Maxim Mikityanskiy <maximmi@...lanox.com> wrote:
>
> > -----Original Message-----
> > From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
> > Sent: 23 January, 2019 16:15
> > To: Maxim Mikityanskiy <maximmi@...lanox.com>
> > Cc: David S. Miller <davem@...emloft.net>; Saeed Mahameed
> > <saeedm@...lanox.com>; Willem de Bruijn <willemb@...gle.com>; Jason Wang
> > <jasowang@...hat.com>; Eric Dumazet <edumazet@...gle.com>;
> > netdev@...r.kernel.org; Eran Ben Elisha <eranbe@...lanox.com>; Tariq Toukan
> > <tariqt@...lanox.com>
> > Subject: Re: [PATCH 3/7] net/ethernet: Add parse_protocol header_ops support
> >
> > On Mon, Jan 14, 2019 at 8:21 AM Maxim Mikityanskiy <maximmi@...lanox.com>
> > wrote:
> > >
> > > The previous commit introduced parse_protocol callback which should
> > > extract the protocol number from the L2 header. Make all Ethernet
> > > devices support it.
> > >
> > > Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>
> > > ---
> > >  include/linux/etherdevice.h |  1 +
> > >  net/ethernet/eth.c          | 13 +++++++++++++
> > >  2 files changed, 14 insertions(+)
> > >
> > > diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
> > > index 2c0af7b00715..e2f3b21cd72a 100644
> > > --- a/include/linux/etherdevice.h
> > > +++ b/include/linux/etherdevice.h
> > > @@ -44,6 +44,7 @@ int eth_header_cache(const struct neighbour *neigh,
> > struct hh_cache *hh,
> > >                      __be16 type);
> > >  void eth_header_cache_update(struct hh_cache *hh, const struct net_device
> > *dev,
> > >                              const unsigned char *haddr);
> > > +__be16 eth_header_parse_protocol(const struct sk_buff *skb);
> >
> > Does not need to be exposed in the header file or exported.
>
> Are you sure? All the other Ethernet header_ops callbacks are exported
> and declared in the header. I'm not sure about the reason why it is done
> in such a way, but my guess is that it will be useful if some driver
> decides to replace one callback in header_ops but to use the default
> ones for the rest of callbacks.

I don't exactly follow this. But I think that many are exported
because Ethernet is so common that of these are also called directly
instead of through header_ops. Looking at other header_ops
implementations, or other such callback structs, shows many examples
where the members are static local functions.

> If the default callbacks were not
> accessible externally, it wouldn't be possible. So, I'm following the
> existing pattern here, and there are reasons for that. What do you think
> about it?