Re: [LSF/MM/BPF TOPIC] Improving iov_iter - and replacing scatterlists

John Hubbard
2025-01-20T19:03:28Z

On 1/20/25 6:22 AM, Leon Romanovsky wrote:
> On Fri, Jan 17, 2025 at 09:16:52PM +0000, David Howells wrote:
>> Hi,
>>
>> I'd like to propose a discussion of two things: firstly, how might we improve
>> iov_iter and, secondly, would it be possible to replace scatterlists.
>
> <...>
>
>> Rumour has it that John Hubbard may be working along similar lines, possibly
>> just in the area of bio_vecs and ITER_BVEC.

I do feel the need to apologize to Leon here, because I've been mostly MIA
ever we talked about this at LPC. Perhaps I'll actually be of some use in
2025. :)

>>
>>
>> [*] Second: Can we replace the uses of scatterlist with iov_iter and reduce
>> the number of iterator classes we have?
>
> <...>
>
> I would say yes to the questions.
>
> Regarding rumors, I don't know, but Christoph, Jason and I are working towards
> this goal. We proposed new DMA API which doesn't need scatterlists and allows
> callers to implement their own data-structures.
>
> See this "[PATCH v6 00/17] Provide a new two step DMA mapping API" series
> https://lore.kernel.org/all/cover.1737106761.git.leon@kernel.org
> and its block layer followup "[RFC PATCH 0/7] Block and NMMe PCI use of
> new DMA mapping API"
> https://lore.kernel.org/all/cover.1730037261.git.leon@kernel.org
>
> Thanks

thanks,
--
John Hubbard