linux-kernel - Re: [PATCH net-next 6/7] xsk: add helper to get &xdp

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Message-ID: <20241220092647.63affabc@kernel.org>
Date: Fri, 20 Dec 2024 09:26:47 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
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>, "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>,
 <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 6/7] xsk: add helper to get &xdp_desc's DMA and
 meta pointer in one go

On Fri, 20 Dec 2024 16:58:57 +0100 Alexander Lobakin wrote:
> > On Wed, 18 Dec 2024 18:44:34 +0100 Alexander Lobakin wrote:  
> >> +	ret = (typeof(ret)){
> >> +		/* Same logic as in xp_raw_get_dma() */
> >> +		.dma	= (pool->dma_pages[addr >> PAGE_SHIFT] &
> >> +			   ~XSK_NEXT_PG_CONTIG_MASK) + (addr & ~PAGE_MASK),
> >> +	};  
> > 
> > This is quite ugly IMHO  
> 
> What exactly: that the logic is copied or how that code (>> & ~ + & ~)
> looks like?
> 
> If the former, I already thought of making a couple internal defs to
> avoid copying.
> If the latter, I also thought of this, just wanted to be clear that it's
> the same as in xp_raw_get_dma(). But it can be refactored to look more
> fancy anyway.
> 
> Or the compound return looks ugly? Or the struct initialization?

Compound using typeof() and the fact it's multi line.

It's a two member struct, which you return by value,
so unlikely to grow. Why not init the members manually?

And you could save the intermediate computations to a temp variable
(addr >> PAGE_SHIFT, addr & ~PAGE_MASK) to make the line shorter.