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

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Message-ID: <AM6PR05MB5879862AB004334C0B85C875D19A0@AM6PR05MB5879.eurprd05.prod.outlook.com>
Date:   Thu, 24 Jan 2019 09:47:58 +0000
From:   Maxim Mikityanskiy <maximmi@...lanox.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.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

> -----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. 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?