linux-kernel - Re: [PATCH net-next 07/12] xsk: add generic XSk &xdp

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Message-ID: <eb2aab4b-ba00-4b9d-ba53-5a5bb544f6fd@intel.com>
Date: Fri, 13 Dec 2024 18:31:59 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
	<pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
	<daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, "Andrii
 Nakryiko" <andrii@...nel.org>, Peter Zijlstra <peterz@...radead.org>, "Josh
 Poimboeuf" <jpoimboe@...nel.org>, "Jose E. Marchesi"
	<jose.marchesi@...cle.com>, Toke Høiland-Jørgensen
	<toke@...hat.com>, Magnus Karlsson <magnus.karlsson@...el.com>, "Maciej
 Fijalkowski" <maciej.fijalkowski@...el.com>, Przemek Kitszel
	<przemyslaw.kitszel@...el.com>, Jason Baron <jbaron@...mai.com>, "Casey
 Schaufler" <casey@...aufler-ca.com>, Nathan Chancellor <nathan@...nel.org>,
	<nex.sw.ncis.osdt.itp.upstreaming@...el.com>, <bpf@...r.kernel.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 07/12] xsk: add generic XSk &xdp_buff -> skb
 conversion

From: Jakub Kicinski <kuba@...nel.org>
Date: Thu, 12 Dec 2024 18:19:44 -0800

> On Wed, 11 Dec 2024 18:26:44 +0100 Alexander Lobakin wrote:
>> +#else /* !CONFIG_PAGE_POOL */
>> +	struct napi_struct *napi;
>> +
>> +	pp = NULL;
>> +	napi = napi_by_id(rxq->napi_id);
>> +	if (likely(napi))
>> +		skb = napi_alloc_skb(napi, len);
>> +	else
>> +		skb = __netdev_alloc_skb_ip_align(rxq->dev, len,
>> +						  GFP_ATOMIC | __GFP_NOWARN);
>> +	if (unlikely(!skb))
>> +		return NULL;
>> +#endif /* !CONFIG_PAGE_POOL */
> 
> What are the chances of having a driver with AF_XDP support 
> and without page pool support? I think it's zero :S

Right, as CONFIG_BPF_SYSCALL selects PAGE_POOL if NET.

I think I wrote this when it wasn't true (before Lorenzo introduced
generic page_pools) and then just forgot to change that ._.

> Can we kill all the if !CONFIG_PAGE_POOL sections and hide
> the entire helper under if CONFIG_PAGE_POLL ?

We can. But I think I'd need to introduce a return-NULL wrapper in case
of !PAGE_POOL to satisfy the linker, as lots of drivers build their XSk
code unconditionally.

Thanks,
Olek