Re: [PATCH net-next 6/7] xsk: add helper to get &xdp_desc's DMA and meta pointer in one go

[Alexander Lobakin]

From: Jakub Kicinski <kuba@xxxxxxxxxx>
Date: Fri, 20 Dec 2024 09:26:47 -0800

> 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?

BTW sometimes such compound initializations are faster than
member-by-member assignment. *Not* in this case, however, so sure,
done already.

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

I'll just derive it into a oneliner to not copy the same stuff again
between functions; also, page helpers like PHYS_PFN() and
offset_in_page() can be used here instead of open-coding.

Merry holidays!
Olek