Re: [PATCH v5 06/10] io_uring/rw: add support to send metadata along with read/write

[Pavel Begunkov <asml.silence@gmail.com>]

On 10/29/24 23:24, Keith Busch wrote:
> On Tue, Oct 29, 2024 at 09:53:58PM +0530, Anuj Gupta wrote:
>> This patch adds the capability of sending metadata along with read/write.
>> A new meta_type field is introduced in SQE which indicates the type of
>> metadata being passed. This meta is represented by a newly introduced
>> 'struct io_uring_meta_pi' which specifies information such as flags,buffer
>> length,seed and apptag. Application sets up a SQE128 ring, prepares
>> io_uring_meta_pi within the second SQE.
>> The patch processes the user-passed information to prepare uio_meta
>> descriptor and passes it down using kiocb->private.
>>
>> Meta exchange is supported only for direct IO.
>> Also vectored read/write operations with meta are not supported
>> currently.
> 
> It looks like it is reasonable to add support for fixed buffers too.
> There would be implications for subsequent patches, mostly patch 10, but
> it looks like we can do that.
> 
> Anyway, this patch mostly looks okay to me. I don't know about the whole
> "meta_type" thing. My understanding from Pavel was wanting a way to
> chain command specific extra options. For example, userspace metadata
> and write hints, and this doesn't look like it can be extended to do
> that.

It makes sense to implement write hints as a meta/attribute type,
but depends on whether it's supposed to be widely supported by
different file types vs it being a block specific feature, and if
SQEs have space for it.

-- 
Pavel Begunkov