io_submit(2) — Linux manual page


IO_SUBMIT(2)              Linux Programmer's Manual             IO_SUBMIT(2)

NAME         top

       io_submit - submit asynchronous I/O blocks for processing

SYNOPSIS         top

       #include <linux/aio_abi.h>          /* Defines needed types */

       int io_submit(io_context_t ctx_id, long nr, struct iocb **iocbpp);

       Note: There is no glibc wrapper for this system call; see NOTES.

DESCRIPTION         top

       The io_submit() system call queues nr I/O request blocks for
       processing in the AIO context ctx_id.  The iocbpp argument should be
       an array of nr AIO control blocks, which will be submitted to context

       The iocb (I/O control block) structure defined in linux/aio_abi.h
       defines the parameters that control the I/O operation.

           #include <linux/aio_abi.h>

           struct iocb {
               __u64   aio_data;
               __u32   PADDED(aio_key, aio_rw_flags);
               __u16   aio_lio_opcode;
               __s16   aio_reqprio;
               __u32   aio_fildes;
               __u64   aio_buf;
               __u64   aio_nbytes;
               __s64   aio_offset;
               __u64   aio_reserved2;
               __u32   aio_flags;
               __u32   aio_resfd;

       The fields of this structure are as follows:

              This data is copied into the data field of the io_event struc‐
              ture upon I/O completion (see io_getevents(2)).

              This is an internal field used by the kernel.  Do not modify
              this field after an io_submit() call.

              This defines the R/W flags passed with structure.  The valid
              values are:

              RWF_APPEND (since Linux 4.16)
                     Append data to the end of the file.  See the descrip‐
                     tion of the flag of the same name in pwritev2(2) as
                     well as the description of O_APPEND in open(2).  The
                     aio_offset field is ignored.  The file offset is not

              RWF_DSYNC (since Linux 4.13)
                     Write operation complete according to requirement of
                     synchronized I/O data integrity.  See the description
                     of the flag of the same name in pwritev2(2) as well the
                     description of O_DSYNC in open(2).

              RWF_HIPRI (since Linux 4.13)
                     High priority request, poll if possible

              RWF_NOWAIT (since Linux 4.14)
                     Don't wait if the I/O will block for operations such as
                     file block allocations, dirty page flush, mutex locks,
                     or a congested block device inside the kernel.  If any
                     of these conditions are met, the control block is re‐
                     turned immediately with a return value of -EAGAIN in
                     the res field of the io_event structure (see

              RWF_SYNC (since Linux 4.13)
                     Write operation complete according to requirement of
                     synchronized I/O file integrity.  See the description
                     of the flag of the same name in pwritev2(2) as well the
                     description of O_SYNC in open(2).

              This defines the type of I/O to be performed by the iocb
              structure.  The valid values are defined by the enum defined
              in linux/aio_abi.h:

                  enum {
                      IOCB_CMD_PREAD = 0,
                      IOCB_CMD_PWRITE = 1,
                      IOCB_CMD_FSYNC = 2,
                      IOCB_CMD_FDSYNC = 3,
                      IOCB_CMD_POLL = 5,
                      IOCB_CMD_NOOP = 6,
                      IOCB_CMD_PREADV = 7,
                      IOCB_CMD_PWRITEV = 8,

              This defines the requests priority.

              The file descriptor on which the I/O operation is to be per‐

              This is the buffer used to transfer data for a read or write

              This is the size of the buffer pointed to by aio_buf.

              This is the file offset at which the I/O operation is to be

              This is the set of flags associated with the iocb structure.
              The valid values are:

                     Asynchronous I/O control must signal the file descrip‐
                     tor mentioned in aio_resfd upon completion.

              IOCB_FLAG_IOPRIO (since Linux 4.18)
                     Interpret the aio_reqprio field as an IOPRIO_VALUE as
                     defined by linux/ioprio.h.

              The file descriptor to signal in the event of asynchronous I/O

RETURN VALUE         top

       On success, io_submit() returns the number of iocbs submitted (which
       may be less than nr, or 0 if nr is zero).  For the failure return,
       see NOTES.

ERRORS         top

       EAGAIN Insufficient resources are available to queue any iocbs.

       EBADF  The file descriptor specified in the first iocb is invalid.

       EFAULT One of the data structures points to invalid data.

       EINVAL The AIO context specified by ctx_id is invalid.  nr is less
              than 0.  The iocb at *iocbpp[0] is not properly initialized,
              the operation specified is invalid for the file descriptor in
              the iocb, or the value in the aio_reqprio field is invalid.

       ENOSYS io_submit() is not implemented on this architecture.

       EPERM  The aio_reqprio field is set with the class IOPRIO_CLASS_RT,
              but the submitting context does not have the CAP_SYS_ADMIN

VERSIONS         top

       The asynchronous I/O system calls first appeared in Linux 2.5.

CONFORMING TO         top

       io_submit() is Linux-specific and should not be used in programs that
       are intended to be portable.

NOTES         top

       Glibc does not provide a wrapper function for this system call.  You
       could invoke it using syscall(2).  But instead, you probably want to
       use the io_submit() wrapper function provided by libaio.

       Note that the libaio wrapper function uses a different type
       (io_context_t) for the ctx_id argument.  Note also that the libaio
       wrapper does not follow the usual C library conventions for
       indicating errors: on error it returns a negated error number (the
       negative of one of the values listed in ERRORS).  If the system call
       is invoked via syscall(2), then the return value follows the usual
       conventions for indicating an error: -1, with errno set to a
       (positive) value that indicates the error.

SEE ALSO         top

       io_cancel(2), io_destroy(2), io_getevents(2), io_setup(2), aio(7)

COLOPHON         top

       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2020-04-11                     IO_SUBMIT(2)

Pages that refer to this page: fcntl(2)fcntl64(2)io_cancel(2)io_destroy(2)io_getevents(2)io_setup(2)syscalls(2)systemd.exec(5)aio(7)