Re: [PATCH 2/3] io_uring/uring_cmd: allow non-iopoll cmds with IORING_SETUP_IOPOLL

[Caleb Sander Mateos <csander@purestorage.com>]

On Thu, Feb 12, 2026 at 7:21 PM Caleb Sander Mateos
<csander@purestorage.com> wrote:
>
> Currently, creating an io_uring with IORING_SETUP_IOPOLL requires all
> requests issued to it to support iopoll. This prevents, for example,
> using ublk zero-copy together with IORING_SETUP_IOPOLL, as ublk
> zero-copy buffer registrations are performed using a uring_cmd. There's
> no technical reason why these non-iopoll uring_cmds can't be supported.
> They will either complete synchronously or via an external mechanism
> that calls io_uring_cmd_done(), so they don't need to be polled.
>
> Allow uring_cmd requests to be issued to IORING_SETUP_IOPOLL io_urings
> even if their files don't implement ->uring_cmd_iopoll(). For these
> uring_cmd requests, skip initializing struct io_kiocb's iopoll fields,
> don't insert the request into iopoll_list, and take the
> io_req_complete_defer() or io_req_task_work_add() path in
> __io_uring_cmd_done() instead of setting the iopoll_completed flag. Also
> allow io_uring_cmd_mark_cancelable() to be called on these uring_cmds.
> Assert that io_uring_cmd_mark_cancelable() is only called on
> non-IORING_SETUP_IOPOLL io_urings or uring_cmds to files that don't
> implement ->uring_cmd_iopoll().
>
> Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
> ---
>  io_uring/io_uring.c  |  4 +++-
>  io_uring/uring_cmd.c | 11 +++++------
>  2 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index c45af82dda3d..4e68a5168894 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -1417,11 +1417,13 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
>
>         if (ret == IOU_ISSUE_SKIP_COMPLETE) {
>                 ret = 0;
>
>                 /* If the op doesn't have a file, we're not polling for it */
> -               if ((req->ctx->flags & IORING_SETUP_IOPOLL) && def->iopoll_queue)
> +               if ((req->ctx->flags & IORING_SETUP_IOPOLL) &&
> +                   def->iopoll_queue && (!io_is_uring_cmd(req) ||
> +                                         req->file->f_op->uring_cmd_iopoll))
>                         io_iopoll_req_issued(req, issue_flags);
>         }
>         return ret;
>  }
>
> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> index ee7b49f47cb5..8df52e8f1c1b 100644
> --- a/io_uring/uring_cmd.c
> +++ b/io_uring/uring_cmd.c
> @@ -108,12 +108,12 @@ void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
>          * Doing cancelations on IOPOLL requests are not supported. Both
>          * because they can't get canceled in the block stack, but also
>          * because iopoll completion data overlaps with the hash_node used
>          * for tracking.
>          */
> -       if (ctx->flags & IORING_SETUP_IOPOLL)
> -               return;
> +       WARN_ON_ONCE(ctx->flags & IORING_SETUP_IOPOLL &&
> +                    req->file->f_op->uring_cmd_iopoll);
>
>         if (!(cmd->flags & IORING_URING_CMD_CANCELABLE)) {
>                 cmd->flags |= IORING_URING_CMD_CANCELABLE;
>                 io_ring_submit_lock(ctx, issue_flags);
>                 hlist_add_head(&req->hash_node, &ctx->cancelable_uring_cmd);
> @@ -165,11 +165,12 @@ void __io_uring_cmd_done(struct io_uring_cmd *ioucmd, s32 ret, u64 res2,
>                 if (req->ctx->flags & IORING_SETUP_CQE_MIXED)
>                         req->cqe.flags |= IORING_CQE_F_32;
>                 io_req_set_cqe32_extra(req, res2, 0);
>         }
>         io_req_uring_cleanup(req, issue_flags);
> -       if (req->ctx->flags & IORING_SETUP_IOPOLL) {
> +       if (req->ctx->flags & IORING_SETUP_IOPOLL &&
> +           req->file->f_op->uring_cmd_iopoll) {

I do worry that the pointer chasing here may be expensive, ->file and
->f_op could both be uncached. Would it make sense to add a flag to
req->flags to indicate whether a request should actually be IOPOLLed?

Thanks,
Caleb

>                 /* order with io_iopoll_req_issued() checking ->iopoll_complete */
>                 smp_store_release(&req->iopoll_completed, 1);
>         } else if (issue_flags & IO_URING_F_COMPLETE_DEFER) {
>                 if (WARN_ON_ONCE(issue_flags & IO_URING_F_UNLOCKED))
>                         return;
> @@ -255,13 +256,11 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
>                 issue_flags |= IO_URING_F_SQE128;
>         if (ctx->flags & (IORING_SETUP_CQE32 | IORING_SETUP_CQE_MIXED))
>                 issue_flags |= IO_URING_F_CQE32;
>         if (io_is_compat(ctx))
>                 issue_flags |= IO_URING_F_COMPAT;
> -       if (ctx->flags & IORING_SETUP_IOPOLL) {
> -               if (!file->f_op->uring_cmd_iopoll)
> -                       return -EOPNOTSUPP;
> +       if (ctx->flags & IORING_SETUP_IOPOLL && file->f_op->uring_cmd_iopoll) {
>                 issue_flags |= IO_URING_F_IOPOLL;
>                 req->iopoll_completed = 0;
>                 if (ctx->flags & IORING_SETUP_HYBRID_IOPOLL) {
>                         /* make sure every req only blocks once */
>                         req->flags &= ~REQ_F_IOPOLL_STATE;
> --
> 2.45.2
>