Re: [PATCH 5/5] io_uring: implement multishot mode for accept

Jens Axboe
2022-05-06T14:42:40Z

On 5/6/22 1:01 AM, Hao Xu wrote:
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 0a83ecc457d1..9febe7774dc3 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -1254,6 +1254,7 @@ static int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags);
> static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer);
> static void io_eventfd_signal(struct io_ring_ctx *ctx);
> static void io_req_tw_post_queue(struct io_kiocb *req, s32 res, u32 cflags);
> +static void io_poll_remove_entries(struct io_kiocb *req);
>
> static struct kmem_cache *req_cachep;
>
> @@ -5690,24 +5691,29 @@ static int io_recv(struct io_kiocb *req, unsigned int issue_flags)
> static int io_accept_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
> {
> struct io_accept *accept = &req->accept;
> + bool multishot;
>
> if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
> return -EINVAL;
> - if (sqe->ioprio || sqe->len || sqe->buf_index)
> + if (sqe->len || sqe->buf_index)
> return -EINVAL;
>
> accept->addr = u64_to_user_ptr(READ_ONCE(sqe->addr));
> accept->addr_len = u64_to_user_ptr(READ_ONCE(sqe->addr2));
> accept->flags = READ_ONCE(sqe->accept_flags);
> accept->nofile = rlimit(RLIMIT_NOFILE);
> + multishot = !!(READ_ONCE(sqe->ioprio) & IORING_ACCEPT_MULTISHOT);

I tend to like:

multishot = READ_ONCE(sqe->ioprio) & IORING_ACCEPT_MULTISHOT) != 0;

as I think it's more readable. But I think we really want it ala:

u16 poll_flags;

poll_flags = READ_ONCE(sqe->ioprio);
if (poll_flags & ~IORING_ACCEPT_MULTISHOT)
return -EINVAL;

...

to ensure that we can add more flags later, hence only accepting this
single flag right now.

Do we need REQ_F_APOLL_MULTI_POLLED, or can we just store whether this
is a multishot request in struct io_accept?

> @@ -5760,7 +5774,35 @@ static int io_accept(struct io_kiocb *req, unsigned int issue_flags)
> ret = io_install_fixed_file(req, file, issue_flags,
> accept->file_slot - 1);
> }
> - __io_req_complete(req, issue_flags, ret, 0);
> +
> + if (req->flags & REQ_F_APOLL_MULTISHOT) {
> + if (ret >= 0) {
> + bool filled;
> +
> + spin_lock(&ctx->completion_lock);
> + filled = io_fill_cqe_aux(ctx, req->cqe.user_data, ret,
> + IORING_CQE_F_MORE);
> + io_commit_cqring(ctx);
> + spin_unlock(&ctx->completion_lock);
> + if (unlikely(!filled)) {
> + io_poll_clean(req);
> + return -ECANCELED;
> + }
> + io_cqring_ev_posted(ctx);
> + goto retry;
> + } else {
> + /*
> + * the apoll multishot req should handle poll
> + * cancellation by itself since the upper layer
> + * who called io_queue_sqe() cannot get errors
> + * happened here.
> + */
> + io_poll_clean(req);
> + return ret;
> + }
> + } else {
> + __io_req_complete(req, issue_flags, ret, 0);
> + }
> return 0;
> }

I'd probably just make that:

if (!(req->flags & REQ_F_APOLL_MULTISHOT)) {
__io_req_complete(req, issue_flags, ret, 0);
return 0;
}
if (ret >= 0) {
bool filled;

spin_lock(&ctx->completion_lock);
filled = io_fill_cqe_aux(ctx, req->cqe.user_data, ret,
IORING_CQE_F_MORE);
io_commit_cqring(ctx);
spin_unlock(&ctx->completion_lock);
if (filled) {
io_cqring_ev_posted(ctx);
goto retry;
}
/* fall through to error case */
ret = -ECANCELED;
}

/*
* the apoll multishot req should handle poll
* cancellation by itself since the upper layer
* who called io_queue_sqe() cannot get errors
* happened here.
*/
io_poll_clean(req);
return ret;

which I think is a lot easier to read and keeps the indentation at a
manageable level and reduces duplicate code.

--
Jens Axboe