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

Hao Xu
2022-05-07T09:13:09Z

在 2022/5/6 下午10:42, Jens Axboe 写道:
> 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?
I think we can do it in this way, but it may be a bit inconvenient if we
add other multishot OPCODE. With REQ_F_APOLL_MULTI_POLLED we can just
check req->flags in the poll arming path, which keeps it op unrelated.
>
>> @@ -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.
Great, thanks, it's better.
>