linux-kernel - Re: [PATCH net-next] xdp: add xdp_skb_reserve

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Message-ID: <BF410EC2-6DFE-46B2-8AF1-4C48309C5F7B@nutanix.com>
Date: Wed, 30 Apr 2025 19:09:08 +0000
From: Jon Kohler <jon@...anix.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
CC: Daniel Borkmann <daniel@...earbox.net>, Jason Wang <jasowang@...hat.com>,
        Andrew Lunn <andrew+netdev@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo
 Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
        Jesper
 Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Simon Horman <horms@...nel.org>,
        "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: [PATCH net-next] xdp: add xdp_skb_reserve_put helper



> On Apr 30, 2025, at 3:04 PM, Willem de Bruijn <willemdebruijn.kernel@...il.com> wrote:
> 
> !-------------------------------------------------------------------|
>  CAUTION: External Email
> 
> |-------------------------------------------------------------------!
> 
> Jon Kohler wrote:
>> 
>> 
>>> On Apr 30, 2025, at 2:40 PM, Daniel Borkmann <daniel@...earbox.net> wrote:
>>> 
>>> !-------------------------------------------------------------------|
>>> CAUTION: External Email
>>> 
>>> |-------------------------------------------------------------------!
>>> 
>>> On 4/30/25 8:25 PM, Willem de Bruijn wrote:
>>>> Jon Kohler wrote:
>>>>> Add helper for calling skb_{put|reserve} to reduce repetitive pattern
>>>>> across various drivers.
>>>>> 
>>>>> Plumb into tap and tun to start.
>>>>> 
>>>>> No functional change intended.
>>>>> 
>>>>> Signed-off-by: Jon Kohler <jon@...anix.com>
>>>>> ---
>>>>> drivers/net/tap.c | 3 +--
>>>>> drivers/net/tun.c | 3 +--
>>>>> include/net/xdp.h | 8 ++++++++
>>>>> net/core/xdp.c    | 3 +--
>>>>> 4 files changed, 11 insertions(+), 6 deletions(-)
>>>> Subjective, but I prefer the existing code. I understand what
>>>> skb_reserve and skb_put do. While xdp_skb_reserve_put adds a layer of
>>>> indirection that I'd have to follow.
>>>> Sometimes deduplication makes sense, sometimes the indirection adds
>>>> more mental load than it's worth. In this case the code savings are
>>>> small. As said, subjective. Happy to hear other opinions.
>>> 
>>> +1, agree with Willem
>> 
>> That’s a fair point. I was also toying with the idea of something like
>> this instead:
>> 
>> e.g.
>> xdp_headroom(xdp) == xdp->data - xdp->data_hard_start
>> … similar to skb_headroom
>> 
>> xdp_length_base(xdp) == xdp->data_end - xdp->data
>> … similar to xdp_get_buff_len, but doesn’t look at frags
>> 
>> then we could do:
>> skb_reserve(skb, xdp_headroom(xdp));
>> skb_put(skb, xdp_length_base(xdp));
>> 
>> Names TBD of course, but thoughts?
>> 
>> That way we keep skb_reserve/put just the same, but have
>> a nice helper like we do for skb_headroom() already
> 
> I like the idea of xdp_headroom and xdk_headlen, similar to
> skb_headroom and skb_headlen.
> 

Sold! I’ll cook it up