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[72.132.29.68]) by smtp.gmail.com with ESMTPSA id y11sm5281321pfl.198.2021.09.05.12.44.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 05 Sep 2021 12:44:52 -0700 (PDT) Subject: Re: [PATCH 6/6] io_uring: enable multishot mode for accept To: Pavel Begunkov , Hao Xu Cc: io-uring@vger.kernel.org, Joseph Qi References: <20210903110049.132958-1-haoxu@linux.alibaba.com> <20210903110049.132958-7-haoxu@linux.alibaba.com> <95387504-3986-77df-7cb4-d136dd4be1ec@linux.alibaba.com> <701e50f5-2444-5b56-749b-1c1affc26ce9@gmail.com> From: Jens Axboe Message-ID: Date: Sun, 5 Sep 2021 13:44:50 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <701e50f5-2444-5b56-749b-1c1affc26ce9@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 9/4/21 4:46 PM, Pavel Begunkov wrote: > On 9/4/21 7:40 PM, Jens Axboe wrote: >> On 9/4/21 9:34 AM, Hao Xu wrote: >>> 在 2021/9/4 上午12:29, Jens Axboe 写道: >>>> On 9/3/21 5:00 AM, Hao Xu wrote: >>>>> Update io_accept_prep() to enable multishot mode for accept operation. >>>>> >>>>> Signed-off-by: Hao Xu >>>>> --- >>>>> fs/io_uring.c | 14 ++++++++++++-- >>>>> 1 file changed, 12 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>>>> index eb81d37dce78..34612646ae3c 100644 >>>>> --- a/fs/io_uring.c >>>>> +++ b/fs/io_uring.c >>>>> @@ -4861,6 +4861,7 @@ 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 is_multishot; >>>>> >>>>> if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL)) >>>>> return -EINVAL; >>>>> @@ -4872,14 +4873,23 @@ static int io_accept_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) >>>>> accept->flags = READ_ONCE(sqe->accept_flags); >>>>> accept->nofile = rlimit(RLIMIT_NOFILE); >>>>> >>>>> + is_multishot = accept->flags & IORING_ACCEPT_MULTISHOT; >>>>> + if (is_multishot && (req->flags & REQ_F_FORCE_ASYNC)) >>>>> + return -EINVAL; >>>> >>>> I like the idea itself as I think it makes a lot of sense to just have >>>> an accept sitting there and generating multiple CQEs, but I'm a bit >>>> puzzled by how you pass it in. accept->flags is the accept4(2) flags, >>>> which can currently be: >>>> >>>> SOCK_NONBLOCK >>>> SOCK_CLOEXEC >>>> >>>> While there's not any overlap here, that is mostly by chance I think. A >>>> cleaner separation is needed here, what happens if some other accept4(2) >>>> flag is enabled and it just happens to be the same as >>>> IORING_ACCEPT_MULTISHOT? >>> Make sense, how about a new IOSQE flag, I saw not many >>> entries left there. >> >> Not quite sure what the best approach would be... The mshot flag only >> makes sense for a few request types, so a bit of a shame to have to >> waste an IOSQE flag on it. Especially when the flags otherwise passed in >> are so sparse, there's plenty of bits there. >> >> Hence while it may not be the prettiest, perhaps using accept->flags is >> ok and we just need some careful code to ensure that we never have any >> overlap. > > Or we can alias with some of the almost-never-used fields like > ->ioprio or ->buf_index. It's not a bad idea, as long as we can safely use flags from eg ioprio for cases where ioprio would never be used. In that sense it's probably safer than using buf_index. The alternative is, as has been brougt up before, adding a flags2 and reserving the last flag in ->flags to say "there are flags in flags2". Not exactly super pretty either, but we'll need to extend them at some point. -- Jens Axboe