Re: [PATCH 0/3] Consistently look up fixed buffers before going async

[Jens Axboe <axboe@kernel.dk>]

On Fri, 21 Mar 2025 12:48:16 -0600, Caleb Sander Mateos wrote:
> To use ublk zero copy, an application submits a sequence of io_uring
> operations:
> (1) Register a ublk request's buffer into the fixed buffer table
> (2) Use the fixed buffer in some I/O operation
> (3) Unregister the buffer from the fixed buffer table
> 
> The ordering of these operations is critical; if the fixed buffer lookup
> occurs before the register or after the unregister operation, the I/O
> will fail with EFAULT or even corrupt a different ublk request's buffer.
> It is possible to guarantee the correct order by linking the operations,
> but that adds overhead and doesn't allow multiple I/O operations to
> execute in parallel using the same ublk request's buffer. Ideally, the
> application could just submit the register, I/O, and unregister SQEs in
> the desired order without links and io_uring would ensure the ordering.
> This mostly works, leveraging the fact that each io_uring SQE is prepped
> and issued non-blocking in order (barring link, drain, and force-async
> flags). But it requires the fixed buffer lookup to occur during the
> initial non-blocking issue.
> 
> [...]

Applied, thanks!

[1/3] io_uring/net: only import send_zc buffer once
      commit: 8e3100fcc5cbba03518b8b5c059624aba5c29d50
[2/3] io_uring/net: import send_zc fixed buffer before going async
      commit: 15f4c96bec5d0791904ee68c0f83ba18cab7466d
[3/3] io_uring/uring_cmd: import fixed buffer before going async
      commit: 70085217bec1eb8bbd19e661da9f1734ed8d35ca

Best regards,
-- 
Jens Axboe