Re: [PATCH V6 7/8] io_uring/uring_cmd: support provide group kernel buffer

[Ming Lei <ming.lei@redhat.com>]

Hi Jens,

On Thu, Oct 10, 2024 at 01:31:21PM -0600, Jens Axboe wrote:
> Hi,
> 
> Discussed this with Pavel, and on his suggestion, I tried prototyping a
> "buffer update" opcode. Basically it works like
> IORING_REGISTER_BUFFERS_UPDATE in that it can update an existing buffer
> registration. But it works as an sqe rather than being a sync opcode.
> 
> The idea here is that you could do that upfront, or as part of a chain,
> and have it be generically available, just like any other buffer that
> was registered upfront. You do need an empty table registered first,
> which can just be sparse. And since you can pick the slot it goes into,
> you can rely on that slot afterwards (either as a link, or just the
> following sqe).
> 
> Quick'n dirty obviously, but I did write a quick test case too to verify
> that:
> 
> 1) It actually works (it seems to)

It doesn't work for ublk zc since ublk needs to provide one kernel buffer
for fs rw & net send/recv to consume, and the kernel buffer is invisible
to userspace. But  __io_register_rsrc_update() only can register userspace
buffer.

Also multiple OPs may consume the buffer concurrently, which can't be
supported by buffer select.


thanks, 
Ming