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 <haoxu@xxxxxxxxxxxxxxxxx>
>>>> ---
>>>> 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
