Re: [PATCH 6/6] io_uring: enable multishot mode for accept

[Jens Axboe <axboe@kernel.dk>]

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@linux.alibaba.com>
> ---
>  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?

-- 
Jens Axboe