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Sat, 04 Sep 2021 15:46:33 -0700 (PDT) Subject: Re: [PATCH 6/6] io_uring: enable multishot mode for accept To: Jens Axboe , 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> From: Pavel Begunkov Message-ID: <701e50f5-2444-5b56-749b-1c1affc26ce9@gmail.com> Date: Sat, 4 Sep 2021 23:46:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: 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 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. > Probably best to solve that issue in include/linux/net.h, ala: > > /* Flags for socket, socketpair, accept4 */ > #define SOCK_CLOEXEC O_CLOEXEC > #ifndef SOCK_NONBLOCK > #define SOCK_NONBLOCK O_NONBLOCK > #endif > > /* > * Only used for io_uring accept4, and deliberately chosen to overlap > * with the O_* file bits for read/write mode so we won't risk overlap > * other flags added for socket/socketpair/accept4 use in the future. > */ > #define SOCK_URING_MULTISHOT 00000001 > > which should be OK, as these overlap with the O_* filespace and the > read/write bits are at the start of that space. > > Should be done as a prep patch and sent out to netdev as well, so we can > get their sign-off on this "hack". If we can get that done, then we have > our flag and we can just stuff it in accept->flags as long as we clear > it before calling into accept from io_uring. > -- Pavel Begunkov