netdev - Re: [PATCH ipsec-next v2 1/2] net: refactor common skb header copy code for re-use

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Message-ID: <ZryJK8W1Acz0L/tU@gauss3.secunet.de>
Date: Wed, 14 Aug 2024 12:38:35 +0200
From: Steffen Klassert <steffen.klassert@...unet.com>
To: Paolo Abeni <pabeni@...hat.com>
CC: Christian Hopps <chopps@...pps.org>, <devel@...ux-ipsec.org>,
	<netdev@...r.kernel.org>, "David S . Miller" <davem@...emloft.net>, "Eric
 Dumazet" <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, "Florian
 Westphal" <fw@...len.de>, Sabrina Dubroca <sd@...asysnail.net>, Simon Horman
	<horms@...nel.org>, Antony Antony <antony@...nome.org>, Christian Hopps
	<chopps@...n.net>
Subject: Re: [PATCH ipsec-next v2 1/2] net: refactor common skb header copy
 code for re-use

On Wed, Aug 14, 2024 at 11:46:56AM +0200, Paolo Abeni wrote:
> On 8/9/24 10:34, Christian Hopps wrote:
> > From: Christian Hopps <chopps@...n.net>
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -1515,7 +1515,7 @@ EXPORT_SYMBOL(napi_consume_skb);
> >   	BUILD_BUG_ON(offsetof(struct sk_buff, field) !=		\
> >   		     offsetof(struct sk_buff, headers.field));	\
> > -static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
> > +void ___copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
> >   {
> >   	new->tstamp		= old->tstamp;
> >   	/* We do not copy old->sk */
> > @@ -1524,6 +1524,12 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
> >   	skb_dst_copy(new, old);
> >   	__skb_ext_copy(new, old);
> >   	__nf_copy(new, old, false);
> > +}
> > +EXPORT_SYMBOL_GPL(___copy_skb_header);
> > +
> > +static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
> > +{
> > +	___copy_skb_header(new, old); >
> >   	/* Note : this field could be in the headers group.
> >   	 * It is not yet because we do not want to have a 16 bit hole
> 
> Could you please point where/how are you going to use this helper? factoring
> out this very core bits of skbuff copy looks quite bug prone - and exporting
> the helper could introduce additional unneeded function calls in the core
> code.

It is supposed to be used in the IPTFS pachset:

https://lore.kernel.org/netdev/20240807211331.1081038-12-chopps@chopps.org/

It was open coded before, but there were some concerns that
IPTFS won't get updated if __copy_skb_header changes.