io_uring_prep_read(3) — Linux manual page


io_uring_prep_read(3)        liburing Manual       io_uring_prep_read(3)

NAME         top

       io_uring_prep_read - prepare I/O read request

SYNOPSIS         top

       #include <liburing.h>

       void io_uring_prep_read(struct io_uring_sqe *sqe,
                               int fd,
                               void *buf,
                               unsigned nbytes,
                               __u64 offset);

DESCRIPTION         top

       The io_uring_prep_read(3) prepares an IO read request. The
       submission queue entry sqe is setup to use the file descriptor fd
       to start reading nbytes into the buffer buf at the specified

       On files that support seeking, if the offset is set to -1, the
       read operation commences at the file offset, and the file offset
       is incremented by the number of bytes read. See read(2) for more
       details. Note that for an async API, reading and updating the
       current file offset may result in unpredictable behavior, unless
       access to the file is serialized. It is not encouraged to use
       this feature, if it's possible to provide the desired IO offset
       from the application or library.

       On files that are not capable of seeking, the offset must be 0 or

       After the read has been prepared it can be submitted with one of
       the submit functions.

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_prep_readv(3),
       io_uring_prep_readv2(3), io_uring_submit(3)

COLOPHON         top

       This page is part of the liburing (A library for io_uring)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for
       this manual page, send it to  This page
       was obtained from the project's upstream Git repository
       ⟨⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-03.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
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       (which is not part of the original manual page), send a mail to

liburing-2.1                November 15, 2021      io_uring_prep_read(3)

Pages that refer to this page: io_uring_get_sqe(3)io_uring_prep_read(3)io_uring_prep_read_fixed(3)io_uring_prep_read_multishot(3)io_uring_prep_readv2(3)io_uring_prep_readv(3)