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

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Message-ID: <CAF=yD-J70yRXKA_B-9XBTHEfDd_Ks3mEicJwvYN9jjeLXOsanw@mail.gmail.com>
Date:   Fri, 25 Jan 2019 08:52:21 -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

> > > > > 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.
>
> Yes, they are called directly indeed, but not all of them. E.g.,
> eth_header_parse is never called directly. On the other hand, look at
> drivers/net/macvlan.c:
>
> static const struct header_ops macvlan_hard_header_ops = {
>         .create         = macvlan_hard_header,
>         .parse          = eth_header_parse,
>         .cache          = eth_header_cache,
>         .cache_update   = eth_header_cache_update,
> };
>
> This is exactly what I am talking about. In order to support it,
> eth_header_parse_protocol needs to be exported. BTW, we should consider
> adding it to macvlan_hard_header_ops, ipvlan_header_ops and all other
> such structures.

Very good point. Okay, export it is then.