io_uring: maintain drain logic for multishot poll requests
Now that we have multishot poll requests, one SQE can emit multiple CQEs. given below example: sqe0(multishot poll)-->sqe1-->sqe2(drain req) sqe2 is designed to issue after sqe0 and sqe1 completed, but since sqe0 is a multishot poll request, sqe2 may be issued after sqe0's event triggered twice before sqe1 completed. This isn't what users leverage drain requests for. Here the solution is to wait for multishot poll requests fully completed. To achieve this, we should reconsider the req_need_defer equation, the original one is: all_sqes(excluding dropped ones) == all_cqes(including dropped ones) This means we issue a drain request when all the previous submitted SQEs have generated their CQEs. Now we should consider multishot requests, we deduct all the multishot CQEs except the cancellation one, In this way a multishot poll request behave like a normal request, so: all_sqes == all_cqes - multishot_cqes(except cancellations) Here we introduce cq_extra for it. Signed-off-by:Hao Xu <haoxu@linux.alibaba.com> Link: https://lore.kernel.org/r/1618298439-136286-1-git-send-email-haoxu@linux.alibaba.com Signed-off-by:
Jens Axboe <axboe@kernel.dk>
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