io_uring_prep_recv_multishot(3) — Linux manual page


io_uring_prep_recv(3)        liburing Manual       io_uring_prep_recv(3)

NAME         top

       io_uring_prep_recv - prepare a recv request

SYNOPSIS         top

       #include <liburing.h>

       void io_uring_prep_recv(struct io_uring_sqe *sqe,
                               int sockfd,
                               void *buf,
                               size_t len,
                               int flags);

       void io_uring_prep_recv_multishot(struct io_uring_sqe *sqe,
                                         int sockfd,
                                         void *buf,
                                         size_t len,
                                         int flags);

DESCRIPTION         top

       The io_uring_prep_recv(3) function prepares a recv request. The
       submission queue entry sqe is setup to use the file descriptor
       sockfd to start receiving the data into the destination buffer
       buf of size len and with modifier flags flags.

       This function prepares an async recv(2) request. See that man
       page for details on the arguments specified to this prep helper.

       The multishot version allows the application to issue a single
       receive request, which repeatedly posts a CQE when data is
       available. It requires length to be 0, the IOSQE_BUFFER_SELECT
       flag to be set and no MSG_WAITALL flag to be set.  Therefore each
       CQE will take a buffer out of a provided buffer pool for
       receiving.  The application should check the flags of each CQE,
       regardless of its result.  If a posted CQE does not have the
       IORING_CQE_F_MORE flag set then the multishot receive will be
       done and the application should issue a new request.  Multishot
       variants are available since kernel 6.0.

       After calling this function, additional io_uring internal
       modifier flags may be set in the SQE ioprio field. The following
       flags are supported:

              If set, io_uring will assume the socket is currently empty
              and attempting to receive data will be unsuccessful. For
              this case, io_uring will arm internal poll and trigger a
              receive of the data when the socket has data to be read.
              This initial receive attempt can be wasteful for the case
              where the socket is expected to be empty, setting this
              flag will bypass the initial receive attempt and go
              straight to arming poll. If poll does indicate that data
              is ready to be received, the operation will proceed.

              Can be used with the CQE IORING_CQE_F_SOCK_NONEMPTY flag,
              which io_uring will set on CQEs after a recv(2) or
              recvmsg(2) operation. If set, the socket still had data to
              be read after the operation completed. Both these flags
              are available since 5.19.

RETURN VALUE         top


ERRORS         top

       The CQE res field will contain the result of the operation. See
       the related man page for details on possible values. Note that
       where synchronous system calls will return -1 on failure and set
       errno to the actual error value, io_uring never uses errno.
       Instead it returns the negated errno directly in the CQE res

SEE ALSO         top

       io_uring_get_sqe(3), io_uring_submit(3), recv(2)

COLOPHON         top

       This page is part of the liburing (A library for io_uring)
       project.  Information about the project can be found at 
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       was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
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liburing-2.2                 March 12, 2022        io_uring_prep_recv(3)