Re: [PATCH v9 06/11] io_uring: introduce attributes for read/write and PI support

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

On 11/14/24 12:16, Christoph Hellwig wrote:
> On Thu, Nov 14, 2024 at 04:15:12PM +0530, Anuj Gupta wrote:
>> PI attribute is supported only for direct IO. Also, vectored read/write
>> operations are not supported with PI currently.

And my apologies Anuj, I've been busy, I hope to take a look
at this series today / tomorrow.

> Eww.  I know it's frustration for your if maintainers give contradicting
> guidance, but this is really an awful interface.  Not only the pointless

Because once you placed it at a fixed location nothing realistically
will be able to reuse it. Not everyone will need PI, but the assumption
that there will be more more additional types of attributes / parameters.

With SQE128 it's also a problem that now all SQEs are 128 bytes regardless
of whether a particular request needs it or not, and the user will need
to zero them for each request.

The discussion continued in the v6 thread, here

https://lore.kernel.org/all/20241031065535.GA26299@lst.de/T/#m12beca2ede2bd2017796adb391bedec9c95d85c3

and a little bit more here:

https://lore.kernel.org/all/20241031065535.GA26299@lst.de/T/#mc3f7a95915a64551e061d37b33a643676c5d87b2

> indirection which make the interface hard to use, but limiting it to
> not support vectored I/O makes it pretty useless.

I'm not sure why that's the case and need to take a look), but I
don't immediately see how it's relevant to that part of the API. It
shouldn't really matter where the main PI structure is located, you
get an iovec pointer and code from there wouldn't be any different.

> I guess I need to do a little read-up on why Pavel wants this, but
> from the block/fs perspective the previous interface made so much
> more sense.

-- 
Pavel Begunkov